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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>SQL Module</h1>
<p>
<p> <center><table cellpadding="4" cellspacing="2" border="0">
<tr bgcolor="#f0f0f0">
<td valign="top"><a href="qsql.html">QSql</a>
<td valign="top"><a href="qsqlcursor.html">QSqlCursor</a>
<td valign="top"><a href="qsqldatabase.html">QSqlDatabase</a>
<td valign="top"><a href="qsqldriver.html">QSqlDriver</a>
<td valign="top"><a href="qsqldriverplugin.html">QSqlDriverPlugin</a>
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<td valign="top"><a href="qsqlfield.html">QSqlField</a>
<td valign="top"><a href="qsqlfieldinfo.html">QSqlFieldInfo</a>
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<td valign="top"><a href="qsqlquery.html">QSqlQuery</a>
<td valign="top"><a href="qsqlrecord.html">QSqlRecord</a>
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<td valign="top" colspan="3" rowspan="1"> See also: <a href="sql-driver.html">Supported Drivers</a>
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<p> <!-- toc -->
<ul>
<li><a href="#1"> Introduction
</a>
<li><a href="#2"> SQL Module Architecture
</a>
<li><a href="#3"> SQL Driver Plugins
</a>
<li><a href="#4"> Connecting to Databases
</a>
<li><a href="#5"> Connecting to a Single Database
</a>
<ul>
<li><a href="#5-1"> Connecting to Multiple Databases
</a>
</ul>
<li><a href="#6"> Executing SQL Commands Using QSqlQuery
</a>
<ul>
<li><a href="#6-1"> Transactions
</a>
<li><a href="#6-2"> Basic Browsing
</a>
<li><a href="#6-3"> Basic Data Manipulation
</a>
<li><a href="#6-4"> Navigating Result Sets
</a>
</ul>
<li><a href="#7"> Using QSqlCursor
</a>
<ul>
<li><a href="#7-1"> Retrieving Records
</a>
<ul>
<li><a href="#7-1-1"> Sorting and Filtering Records
</a>
<li><a href="#7-1-2"> Extracting Data
</a>
</ul>
<li><a href="#7-2"> Manipulating Records
</a>
<ul>
<li><a href="#7-2-1"> Inserting Records
</a>
<li><a href="#7-2-2"> Updating Records
</a>
<li><a href="#7-2-3"> Deleting Records
</a>
</ul>
</ul>
<li><a href="#8"> Data-Aware Widgets
</a>
<ul>
<li><a href="#8-1"> Data-Aware Tables
</a>
<li><a href="#8-2"> Creating Data-Aware Forms
</a>
<ul>
<li><a href="#8-2-1"> Displaying a Record
</a>
<li><a href="#8-2-2"> Displaying a Record in a Data Form
</a>
<li><a href="#8-2-3"> Editing a Record
</a>
</ul>
<li><a href="#8-3"> Custom Editor Widgets
</a>
<ul>
<li><a href="#8-3-1"> Custom Editor Widgets for Tables
</a>
</ul>
</ul>
<li><a href="#9"> Subclassing QSqlCursor
</a>
<li><a href="#10"> The Example Tables
</a>
</ul>
<!-- endtoc -->
<p> <a name="Introduction"></a>
<h2> Introduction
</h2>
<a name="1"></a><p> Qt's SQL classes help you provide seamless database integration to
your Qt applications.
<p> <blockquote>
This overview assumes that you have at least a basic knowledge of SQL.
You should be able to understand simple <tt>SELECT</tt>, <tt>INSERT</tt>, <tt>UPDATE</tt>
and <tt>DELETE</tt> commands. Although the <a href="qsqlcursor.html">QSqlCursor</a> class provides an
interface to database browsing and editing that does not <em>require</em> a
knowledge of SQL, a basic understanding of SQL is highly recommended. A
standard text covering SQL databases is <em>An Introduction to Database Systems (7th ed.)</em> by C. J. Date, ISBN 0201385902.
</blockquote>
<p> Whilst this module overview presents the classes from a purely
programmatic point of view the <a href="designer-manual.html">Qt
Designer</a> manual's "Creating Database Applications" chapter
takes a higher-level approach demonstrating how to set up
master-detail relationships between widgets, perform drilldown and
handle foreign key lookups.
<p> This document is divided into six sections:
<p> <a href="#Architecture">SQL Module Architecture</a>. This describes
how the classes fit together.
<p> <a href="#Connecting_to_Databases">Connecting to Databases</a>.
This section explains how to set up database connections using the <a href="qsqldatabase.html">QSqlDatabase</a> class.
<p> <a href="#Executing_SQL_commands">Executing SQL Commands</a>. This
section demonstrates how to issue the standard data manipulation
commands, <tt>SELECT</tt>, <tt>INSERT</tt>, <tt>UPDATE</tt> and <tt>DELETE</tt> on tables in
the database (although any valid SQL statement can be sent to the
database). The focus is purely on database interaction using <a href="qsqlquery.html">QSqlQuery</a>.
<p> <a href="#Using_QSqlCursor">Using Cursors</a>. This section explains
how to use the <a href="qsqlcursor.html">QSqlCursor</a> class which provides a simpler API than the
raw SQL used with <a href="qsqlquery.html">QSqlQuery</a>.
<p> <a href="#Data-Aware_Widgets">Data-Aware Widgets</a>. This section shows
how to programmatically link your database to the user interface. In
this section we introduce the <a href="qdatatable.html">QDataTable</a>, <a href="qsqlform.html">QSqlForm</a>, <a href="qsqlpropertymap.html">QSqlPropertyMap</a> and <a href="qsqleditorfactory.html">QSqlEditorFactory</a> classes and demonstrate how to
use custom data-aware widgets. <a href="designer-manual.html">Qt
Designer</a> provides an easy visual way of achieving the same
thing. See the <a href="designer-manual.html">Qt Designer</a> manual,
<a href="qdatabrowser.html">QDataBrowser</a> and <a href="qdataview.html">QDataView</a> for more information.
<p> <a href="#Subclassing_QSqlCursor">Subclassing QSqlCursor</a>. This
section gives examples of subclassing QSqlCursor. Subclassing can be
used to provide default and calculated values for fields (such as
auto-numbered primary index fields), and to display calculated data,
e.g. showing names rather than ids of foreign keys.
<p> All the examples in this document use the tables defined in the
<a href="#Example_Tables">Example Tables</a> section.
<p> <a name="Architecture"></a>
<h2> SQL Module Architecture
</h2>
<a name="2"></a><p> The SQL classes are divided into three layers:
<p> <em>User Interface Layer.</em> These classes provide data-aware widgets
that can be connected to tables or views in the database (by using a
<a href="qsqlcursor.html">QSqlCursor</a> as a data source). End users can interact directly with
these widgets to browse or edit data. <a href="designer-manual.html">Qt
Designer</a> is fully integrated with the SQL classes and can be
used to create data-aware forms. The data-aware widgets can also be
programmed directly with your own C++ code. The classes that support
this layer include <a href="qsqleditorfactory.html">QSqlEditorFactory</a>, <a href="qsqlform.html">QSqlForm</a>, <a href="qsqlpropertymap.html">QSqlPropertyMap</a>, <a href="qdatatable.html">QDataTable</a>, <a href="qdatabrowser.html">QDataBrowser</a> and <a href="qdataview.html">QDataView</a>.
<p> <em>SQL API Layer.</em> These classes provide access to databases.
Connections are made using the <a href="qsqldatabase.html">QSqlDatabase</a> class. Database
interaction is achieved either by using the <a href="qsqlquery.html">QSqlQuery</a> class and
executing SQL commands directly or by using the higher level <a href="qsqlcursor.html">QSqlCursor</a> class which composes SQL commands automatically. In
addition to <a href="qsqldatabase.html">QSqlDatabase</a>, <a href="qsqlcursor.html">QSqlCursor</a> and <a href="qsqlquery.html">QSqlQuery</a>, the SQL
API layer is supported by <a href="qsqlerror.html">QSqlError</a>, <a href="qsqlfield.html">QSqlField</a>, <a href="qsqlfieldinfo.html">QSqlFieldInfo</a>,
<a href="qsqlindex.html">QSqlIndex</a>, <a href="qsqlrecord.html">QSqlRecord</a> and <a href="qsqlrecordinfo.html">QSqlRecordInfo</a>.
<p> <em>Driver Layer.</em> This comprises three classes, <a href="qsqlresult.html">QSqlResult</a>, <a href="qsqldriver.html">QSqlDriver</a> and QSqlDriverFactoryInterface. This layer provides the
low level bridge between the database and the SQL classes. This layer
is <a href="sql-driver.html">documented separately</a> since it is
only relevant to driver writers, and is rarely used in standard
database application programming. See <a href="sql-driver.html">here</a> for more information on implementing a Qt SQL driver plugin.
<p> <a name="Plugins"></a>
<h2> SQL Driver Plugins
</h2>
<a name="3"></a><p> The Qt SQL module can dynamically load new drivers at runtime using
the <a href="plugins-howto.html">Plugins</a>.
<p> The <a href="sql-driver.html">SQL driver documentation</a> describes
how to build plugins for specific database management systems.
<p> Once a plugin is built, Qt will automatically load it, and the driver
will be available for use by <a href="qsqldatabase.html">QSqlDatabase</a> (see <a href="qsqldatabase.html#drivers">QSqlDatabase::drivers</a>()
for more information).
<p> <a name="Connecting_to_Databases"></a>
<h2> Connecting to Databases
</h2>
<a name="4"></a><p> At least one database connection must be created and opened before the
<a href="qsqlquery.html">QSqlQuery</a> or <a href="qsqlcursor.html">QSqlCursor</a> classes can be used.
<p> If the application only needs a single database connection, the <a href="qsqldatabase.html">QSqlDatabase</a> class can create a connection which is used by default
for all SQL operations. If multiple database connections are required
these can easily be set up.
<p> <a href="qsqldatabase.html">QSqlDatabase</a> requires the <a href="qsqldatabase-h.html">qsqldatabase.h</a> header file.
<p> <a name="Connecting_to_a_Single_Database"></a>
<h2> Connecting to a Single Database
</h2>
<a name="5"></a><p> Making a database connection is a simple three step process: activate
the driver, set up the connection information, and open the
connection.
<p>
<pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qsqldatabase-h.html">qsqldatabase.h</a>>
#include "../connection.h"
int main( int argc, char *argv[] )
{
<a href="qapplication.html">QApplication</a> app( argc, argv, FALSE );
<a name="x2141"></a> <a href="qsqldatabase.html">QSqlDatabase</a> *defaultDB = QSqlDatabase::<a href="qsqldatabase.html#addDatabase">addDatabase</a>( DB_SALES_DRIVER );
<a name="x2143"></a> defaultDB-><a href="qsqldatabase.html#setDatabaseName">setDatabaseName</a>( DB_SALES_DBNAME );
<a name="x2146"></a> defaultDB-><a href="qsqldatabase.html#setUserName">setUserName</a>( DB_SALES_USER );
<a name="x2145"></a> defaultDB-><a href="qsqldatabase.html#setPassword">setPassword</a>( DB_SALES_PASSWD );
<a name="x2144"></a> defaultDB-><a href="qsqldatabase.html#setHostName">setHostName</a>( DB_SALES_HOST );
<a name="x2142"></a> if ( defaultDB-><a href="qsqldatabase.html#open">open</a>() ) {
// Database successfully opened; we can now issue SQL commands.
}
return 0;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-connect1-main-cpp.html">sql/overview/connect1/main.cpp</a>
</em></p>
</blockquote><p> First we activate the driver by calling <a href="qsqldatabase.html#addDatabase">QSqlDatabase::addDatabase</a>(),
passing the name of the driver we wish to use for this connection. At
the time of writing the available drivers are: <a href="sql-driver.html#QODBC3">QODBC3</a> (Open Database
Connectivity, includes Microsoft SQL Server support), <a href="sql-driver.html#QOCI8">QOCI8</a> (Oracle 8 and 9),
<a href="sql-driver.html#QTDS7">QTDS7</a> (Sybase Adaptive Server), <a href="sql-driver.html#QPSQL7">QPSQL7</a> (PostgreSQL 6 and 7),
<a href="sql-driver.html#QMYSQL3">QMYSQL3</a> (MySQL), <a href="sql-driver.html#QDB2">QDB2</a> (IBM DB2), <a href="sql-driver.html#QSQLITE">QSQLITE</a> (SQLite) and <a href="sql-driver.html#QIBASE">QIBASE</a> (Interbase).
Note that some of these drivers aren't included in the Qt Open Source Edition; see
the <tt>README</tt> files for details.
<p> The connection which is created becomes the application's default
database connection and will be used by the Qt SQL classes if no
other database is specified.
<p> Second we call setDatabaseName(), setUserName(), setPassword() and
setHostName() to initialize the connection information. Note that for
the QOCI8 (Oracle 8 and 9) driver the TNS Service Name must be passed
to setDatbaseName(). When connecting to ODBC data sources the Data
Source Name (DSN) should be used in the setDatabaseName() call.
<p> Third we call open() to open the database and give us access to the
data. If this call fails it will return FALSE; error information can
be obtained from <a href="qsqldatabase.html#lastError">QSqlDatabase::lastError</a>().
<p> <a name="Connecting_to_Multiple_Databases"></a>
<h3> Connecting to Multiple Databases
</h3>
<a name="5-1"></a><p> Connecting to multiple databases is achieved using the two argument form
of <a href="qsqldatabase.html#addDatabase">QSqlDatabase::addDatabase</a>() where the second argument is a unique
identifier distinguishing the connection.
<p> In the example below we have moved the connections into their own
function, <tt>createConnections()</tt>, and added some basic error handling.
<p> <pre>
#define DB_SALES_DRIVER "QPSQL7"
#define DB_SALES_DBNAME "sales"
#define DB_SALES_USER "salesperson"
#define DB_SALES_PASSWD "salesperson"
#define DB_SALES_HOST "database.domain.no"
#define DB_ORDERS_DRIVER "QOCI8"
#define DB_ORDERS_DBNAME "orders"
#define DB_ORDERS_USER "orderperson"
#define DB_ORDERS_PASSWD "orderperson"
#define DB_ORDERS_HOST "database.domain.no"
bool createConnections();
</pre>
<p> We set up some constants and also declare the <tt>createConnections()</tt>
function in <tt>connection.h</tt>.
<p>
<pre> #include <<a href="qsqldatabase-h.html">qsqldatabase.h</a>>
#include "connection.h"
bool createConnections()
{
<a name="x2147"></a> <a href="qsqldatabase.html">QSqlDatabase</a> *defaultDB = QSqlDatabase::<a href="qsqldatabase.html#addDatabase">addDatabase</a>( DB_SALES_DRIVER );
<a name="x2150"></a> defaultDB-><a href="qsqldatabase.html#setDatabaseName">setDatabaseName</a>( DB_SALES_DBNAME );
<a name="x2153"></a> defaultDB-><a href="qsqldatabase.html#setUserName">setUserName</a>( DB_SALES_USER );
<a name="x2152"></a> defaultDB-><a href="qsqldatabase.html#setPassword">setPassword</a>( DB_SALES_PASSWD );
<a name="x2151"></a> defaultDB-><a href="qsqldatabase.html#setHostName">setHostName</a>( DB_SALES_HOST );
<a name="x2149"></a> if ( ! defaultDB-><a href="qsqldatabase.html#open">open</a>() ) {
<a name="x2148"></a> <a href="qapplication.html#qWarning">qWarning</a>( "Failed to open sales database: " + defaultDB-><a href="qsqldatabase.html#lastError">lastError</a>().text() );
return FALSE;
}
<a href="qsqldatabase.html">QSqlDatabase</a> *oracle = QSqlDatabase::<a href="qsqldatabase.html#addDatabase">addDatabase</a>( DB_ORDERS_DRIVER, "ORACLE" );
oracle-><a href="qsqldatabase.html#setDatabaseName">setDatabaseName</a>( DB_ORDERS_DBNAME );
oracle-><a href="qsqldatabase.html#setUserName">setUserName</a>( DB_ORDERS_USER );
oracle-><a href="qsqldatabase.html#setPassword">setPassword</a>( DB_ORDERS_PASSWD );
oracle-><a href="qsqldatabase.html#setHostName">setHostName</a>( DB_ORDERS_HOST );
if ( ! oracle-><a href="qsqldatabase.html#open">open</a>() ) {
<a href="qapplication.html#qWarning">qWarning</a>( "Failed to open orders database: " + oracle-><a href="qsqldatabase.html#lastError">lastError</a>().text() );
return FALSE;
}
<a href="qsqlquery.html">QSqlQuery</a> q(QString::null, defaultDB);
<a name="x2154"></a> q.<a href="qsqlquery.html#exec">exec</a>("create table people (id integer primary key, name char(40))");
q.<a href="qsqlquery.html#exec">exec</a>("create table staff (id integer primary key, forename char(40), "
"surname char(40), salary float, statusid integer)");
q.<a href="qsqlquery.html#exec">exec</a>("create table status (id integer primary key, name char(30))");
q.<a href="qsqlquery.html#exec">exec</a>("create table creditors (id integer primary key, forename char(40), "
"surname char(40), city char(30))");
q.<a href="qsqlquery.html#exec">exec</a>("create table prices (id integer primary key, name char(40), price float)");
q.<a href="qsqlquery.html#exec">exec</a>("create table invoiceitem (id integer primary key, "
"pricesid integer, quantity integer, paiddate date)");
<a href="qsqlquery.html">QSqlQuery</a> q2(QString::null, oracle);
q2.<a href="qsqlquery.html#exec">exec</a>("create table people (id integer primary key, name char(40))");
return TRUE;
}
</pre><blockquote><p align="center"><em> From <a href="sql.html">sql/overview/connection.cpp</a>
</em></p>
</blockquote><p> We've chosen to isolate database connection in our <tt>createConnections()</tt> function.cpp.
<p> <a name="create_connections"></a>
<pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qsqldatabase-h.html">qsqldatabase.h</a>>
#include "../connection.h"
int main( int argc, char *argv[] )
{
<a href="qapplication.html">QApplication</a> app( argc, argv, FALSE );
if ( createConnections() ) {
// Databases successfully opened; get pointers to them:
<a name="x2155"></a> <a href="qsqldatabase.html">QSqlDatabase</a> *oracledb = QSqlDatabase::<a href="qsqldatabase.html#database">database</a>( "ORACLE" );
// Now we can now issue SQL commands to the oracle connection
// or to the default connection
}
return 0;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-create_connections-main-cpp.html">sql/overview/create_connections/main.cpp</a>
</em></p>
</blockquote><p> The static function <a href="qsqldatabase.html#database">QSqlDatabase::database</a>() can be called from
anywhere to provide a pointer to a database connection. If we call it
without a parameter it will return the default connection. If called
with the identifier we've used for a connection, e.g. "ORACLE", in the
above example, it will return a pointer to the specified connection.
<p> If you create a <tt>main.cpp</tt> using <a href="designer-manual.html">Qt
Designer</a>, it will <em>not</em> include our example
createConnections() function. This means that applications that
preview correctly in <a href="designer-manual.html">Qt Designer</a>
will not run unless you implement your own database connections
function.
<p> Note that in the code above the ODBC connection was not named and is
therefore used as the default connection. <a href="qsqldatabase.html">QSqlDatabase</a> maintains
ownership of the pointers returned by the addDatabase() static
function. To remove a database from the list of maintained
connections, first close the database with <a href="qsqldatabase.html#close">QSqlDatabase::close</a>(), and
then remove it using the static function
<a href="qsqldatabase.html#removeDatabase">QSqlDatabase::removeDatabase</a>().
<p> <a name="Executing_SQL_commands"></a>
<h2> Executing SQL Commands Using <a href="qsqlquery.html">QSqlQuery</a>
</h2>
<a name="6"></a><p> The <a href="qsqlquery.html">QSqlQuery</a> class provides an interface for executing SQL commands.
It also has functions for navigating through the result sets of <tt>SELECT</tt>
queries and for retrieving individual records and field values.
<p> The <a href="qsqlcursor.html">QSqlCursor</a> class described in the next section inherits from <a href="qsqlquery.html">QSqlQuery</a> and provides a higher level interface that composes SQL
commands for us. <a href="qsqlcursor.html">QSqlCursor</a> is particularly easy to integrate with
on-screen widgets. Programmers unfamiliar with SQL can safely skip this
section and use the <a href="qsqlcursor.html">QSqlCursor</a> class covered in
<a href="#Using_QSqlCursor">"Using QSqlCursor"</a>.
<p> <a name="Transactions"></a>
<h3> Transactions
</h3>
<a name="6-1"></a><p> If the underlying database engine supports transactions
<a href="qsqldriver.html#hasFeature">QSqlDriver::hasFeature</a>( QSqlDriver::Transactions ) will return TRUE.
You can use <a href="qsqldatabase.html#transaction">QSqlDatabase::transaction</a>() to initiate a transaction,
followed by the SQL commands you want to execute within the context of
the transaction, and then either <a href="qsqldatabase.html#commit">QSqlDatabase::commit</a>() or
<a href="qsqldatabase.html#rollback">QSqlDatabase::rollback</a>().
<p> <a name="Basic_Browsing"></a>
<h3> Basic Browsing
</h3>
<a name="6-2"></a><p>
<pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qsqldatabase-h.html">qsqldatabase.h</a>>
#include <<a href="qsqlquery-h.html">qsqlquery.h</a>>
#include "../connection.h"
int main( int argc, char *argv[] )
{
<a href="qapplication.html">QApplication</a> app( argc, argv, FALSE );
if ( createConnections() ) {
<a name="x2156"></a> <a href="qsqldatabase.html">QSqlDatabase</a> *oracledb = QSqlDatabase::<a href="qsqldatabase.html#database">database</a>( "ORACLE" );
// Copy data from the oracle database to the ODBC (default)
// database
<a href="qsqlquery.html">QSqlQuery</a> target;
<a href="qsqlquery.html">QSqlQuery</a> query( "SELECT id, name FROM people", oracledb );
<a name="x2158"></a> if ( query.<a href="qsqlquery.html#isActive">isActive</a>() ) {
<a name="x2159"></a> while ( query.<a href="qsqlquery.html#next">next</a>() ) {
<a name="x2157"></a> target.<a href="qsqlquery.html#exec">exec</a>( "INSERT INTO people ( id, name ) VALUES ( " +
<a name="x2160"></a> query.<a href="qsqlquery.html#value">value</a>(0).toString() +
", '" + query.<a href="qsqlquery.html#value">value</a>(1).toString() + "' )" );
}
}
}
return 0;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-basicbrowsing-main-cpp.html">sql/overview/basicbrowsing/main.cpp</a>
</em></p>
</blockquote><p> In the example above we've added an additional header file,
<a href="qsqlquery-h.html">qsqlquery.h</a>. The first query we create, <tt>target</tt>, uses the default
database and is initially empty. For the second query, <tt>q</tt>, we specify
the "ORACLE" database that we want to retrieve records from. Both the
database connections were set up in the createConnections() function we
wrote earlier.
<p> After creating the initial <tt>SELECT</tt> statement, isActive() is checked
to see if the query executed successfully. The next() function is
used to iterate through the query results. The value() function
returns the contents of fields as QVariants. The insertions are
achieved by creating and executing queries against the default
database using the <tt>target</tt> <a href="qsqlquery.html">QSqlQuery</a>.
<p> Note that this example and all the other examples in this document use
the tables defined in the <a href="#Example_Tables">Example Tables</a>
section.
<p>
<pre> int count = 0;
<a name="x2162"></a> if ( query.<a href="qsqlquery.html#isActive">isActive</a>() ) {
<a name="x2163"></a> while ( query.<a href="qsqlquery.html#next">next</a>() ) {
<a name="x2161"></a> target.<a href="qsqlquery.html#exec">exec</a>( "INSERT INTO people ( id, name ) VALUES ( " +
<a name="x2165"></a> query.<a href="qsqlquery.html#value">value</a>(0).toString() +
", '" + query.<a href="qsqlquery.html#value">value</a>(1).toString() + "' )" );
if ( target.<a href="qsqlquery.html#isActive">isActive</a>() )
<a name="x2164"></a> count += target.<a href="qsqlquery.html#numRowsAffected">numRowsAffected</a>();
}
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-basicbrowsing2-main-cpp.html">sql/overview/basicbrowsing2/main.cpp</a>
</em></p>
</blockquote><p> The above code introduces a count of how many records are successfully
inserted. Note that isActive() returns FALSE if the query, e.g. the
insertion, fails. numRowsAffected() returns -1 if the number of rows
cannot be determined, e.g. if the query fails.
<p> <a name="Basic_Data_Manipulation"></a>
<h3> Basic Data Manipulation
</h3>
<a name="6-3"></a><p>
<pre> ** $Id: qt/main.cpp 3.3.8 edited Jan 11 14:37 $
**
** Copyright (C) 1992-2007 Trolltech ASA. All rights reserved.
**
** This file is part of an example program for Qt. This example
** program may be used, distributed and modified without limitation.
**
*****************************************************************************/
#include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qsqldatabase-h.html">qsqldatabase.h</a>>
#include <<a href="qsqlquery-h.html">qsqlquery.h</a>>
#include "../connection.h"
bool createConnections();
int main( int argc, char *argv[] )
{
<a href="qapplication.html">QApplication</a> app( argc, argv, FALSE );
int rows = 0;
if ( createConnections() ) {
<a href="qsqlquery.html">QSqlQuery</a> query( "INSERT INTO staff ( id, forename, surname, salary ) "
"VALUES ( 1155, 'Ginger', 'Davis', 50000 )" );
<a name="x2168"></a><a name="x2167"></a> if ( query.<a href="qsqlquery.html#isActive">isActive</a>() ) rows += query.<a href="qsqlquery.html#numRowsAffected">numRowsAffected</a>() ;
<a name="x2166"></a> query.<a href="qsqlquery.html#exec">exec</a>( "UPDATE staff SET salary=60000 WHERE id=1155" );
if ( query.<a href="qsqlquery.html#isActive">isActive</a>() ) rows += query.<a href="qsqlquery.html#numRowsAffected">numRowsAffected</a>() ;
query.<a href="qsqlquery.html#exec">exec</a>( "DELETE FROM staff WHERE id=1155" );
if ( query.<a href="qsqlquery.html#isActive">isActive</a>() ) rows += query.<a href="qsqlquery.html#numRowsAffected">numRowsAffected</a>() ;
}
return ( rows == 3 ) ? 0 : 1;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-basicdatamanip-main-cpp.html">sql/overview/basicdatamanip/main.cpp</a>
</em></p>
</blockquote><p> This example demonstrates straightforward SQL DML (data manipulation
language) commands. Since we did not specify a database in the <a href="qsqlquery.html">QSqlQuery</a> constructor the default database is used. <a href="qsqlquery.html">QSqlQuery</a> objects
can also be used to execute SQL DDL (data definition language) commands
such as <tt>CREATE TABLE</tt> and <tt>CREATE INDEX</tt>.
<p> <a name="Navigating_Result_Sets"></a>
<h3> Navigating Result Sets
</h3>
<a name="6-4"></a><p> Once a <tt>SELECT</tt> query has been executed successfully we have access
to the result set of records that matched the query criteria. We have
already used one of the navigation functions, next(), which can be
used alone to step sequentially through the records. <a href="qsqlquery.html">QSqlQuery</a> also
provides first(), last() and prev(). After any of these commands we
can check that we are on a valid record by calling isValid().
<p> We can also navigate to any arbitrary record using seek(). The
first record in the dataset is zero. The number of the last record is
size() - 1. Note that not all databases provide the size of a
<tt>SELECT</tt> query and in such cases size() returns -1.
<p>
<pre> if ( createConnections() ) {
<a href="qsqlquery.html">QSqlQuery</a> query( "SELECT id, name FROM people ORDER BY name" );
<a name="x2171"></a> if ( ! query.<a href="qsqlquery.html#isActive">isActive</a>() ) return 1; // Query failed
int i;
<a name="x2174"></a> i = query.<a href="qsqlquery.html#size">size</a>(); // In this example we have 9 records; i == 9.
<a name="x2170"></a> query.<a href="qsqlquery.html#first">first</a>(); // Moves to the first record.
<a name="x2169"></a> i = query.<a href="qsqlquery.html#at">at</a>(); // i == 0
<a name="x2172"></a> query.<a href="qsqlquery.html#last">last</a>(); // Moves to the last record.
i = query.<a href="qsqlquery.html#at">at</a>(); // i == 8
<a name="x2173"></a> query.<a href="qsqlquery.html#seek">seek</a>( query.<a href="qsqlquery.html#size">size</a>() / 2 ); // Moves to the middle record.
i = query.<a href="qsqlquery.html#at">at</a>(); // i == 4
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-navigating-main-cpp.html">sql/overview/navigating/main.cpp</a>
</em></p>
</blockquote><p> The example above shows some of the navigation functions in use.
<p> Not all drivers support size(), but we can interrogate the driver to
find out:
<p> <pre>
<a href="qsqldatabase.html">QSqlDatabase</a>* defaultDB = QSqlDatabase::<a href="qsqldatabase.html#database">database</a>();
if ( defaultDB-><a href="qsqldatabase.html#driver">driver</a>()->hasFeature( QSqlDriver::QuerySize ) ) {
// QSqlQuery::size() supported
}
else {
// QSqlQuery::size() cannot be relied upon
}
</pre>
<p> Once we have located the record we are interested in we may wish to
retrieve data from it.
<p>
<pre> if ( createConnections() ) {
<a href="qsqlquery.html">QSqlQuery</a> query( "SELECT id, surname FROM staff" );
<a name="x2175"></a> if ( query.<a href="qsqlquery.html#isActive">isActive</a>() ) {
<a name="x2176"></a> while ( query.<a href="qsqlquery.html#next">next</a>() ) {
<a href="qapplication.html#qDebug">qDebug</a>( query.<a href="qsqlquery.html#value">value</a>(0).toString() + ": " +
<a name="x2177"></a> query.<a href="qsqlquery.html#value">value</a>(1).toString() );
}
}
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-retrieve1-main-cpp.html">sql/overview/retrieve1/main.cpp</a>
</em></p>
</blockquote><p> Note that if you wish to iterate through the record set in order the
only navigation function you need is next().
<p> Tip: The lastQuery() function returns the text of the last query
executed. This can be useful to check that the query you think is being
executed is the one actually being executed.
<p> <a name="Using_QSqlCursor"></a>
<h2> Using <a href="qsqlcursor.html">QSqlCursor</a>
</h2>
<a name="7"></a><p> The <a href="qsqlcursor.html">QSqlCursor</a> class provides a high level interface to browsing and
editing records in SQL database tables or views without the need to
write your own SQL.
<p> QSqlCursor can do almost everything that <a href="qsqlquery.html">QSqlQuery</a> can, with two
exceptions. Since cursors represent tables or views within the
database, by default, <a href="qsqlcursor.html">QSqlCursor</a> objects retrieve all the fields of
each record in the table or view whenever navigating to a new
record. If only some fields are relevant simply confine your
processing to those and ignore the others. Or, manually disable the
generation of certain fields using <a href="qsqlrecord.html#setGenerated">QSqlRecord::setGenerated</a>(). Another
approach is to create a <tt>VIEW</tt> which only presents the fields you're
interested in; but note that some databases do not support editable
views. So if you really don't want to retrieve all the fields in the
cursor, then you should use a <a href="qsqlquery.html">QSqlQuery</a> instead, and customize the
query to suit your needs. You can edit records using a <a href="qsqlcursor.html">QSqlCursor</a>
providing that the table or view has a primary index that uniquely
distinguishes each record. If this condition is not met then you'll
need to use a <a href="qsqlquery.html">QSqlQuery</a> for edits.
<p> <a href="qsqlcursor.html">QSqlCursor</a> operates on a single record at a time. Whenever performing
an insert, update or delete using QSqlCursor, only a single record in
the database is affected. When navigating through records in the
cursor, only one record at a time is available in application code.
In addition, QSqlCursor maintains a separate 'edit buffer' which is
used to make changes to a single record in the database. The edit
buffer is maintained in a separate memory area, and is unnaffected by
the 'navigation buffer' which changes as the cursor moves from record
to record.
<p> Before we can use <a href="qsqlcursor.html">QSqlCursor</a> objects we must first create and open
a database connection. Connecting is described in the <a href="#Connecting_to_Databases">Connecting to Databases</a> section
above. For the examples that follow we will assume that the
connections have been created using the createConnections() function
defined in the <a href="#create_connections">QSqlDatabase example</a>
presented earlier.
<p> In the <a href="#Data-Aware_Widgets">data-aware widgets</a> section that
follows this one we show how to link widgets to database cursors. Once
we have a knowledge of both cursors and data-aware widgets we can
discuss <a href="#Subclassing_QSqlCursor">subclassing QSqlCursor</a>.
<p> The <a href="qsqlcursor.html">QSqlCursor</a> class requires the <a href="qsqlcursor-h.html">qsqlcursor.h</a> header file.
<p> <a name="Retrieving_Records"></a>
<h3> Retrieving Records
</h3>
<a name="7-1"></a><p>
<pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qsqldatabase-h.html">qsqldatabase.h</a>>
#include <<a href="qsqlcursor-h.html">qsqlcursor.h</a>>
#include "../connection.h"
int main( int argc, char *argv[] )
{
<a href="qapplication.html">QApplication</a> app( argc, argv );
if ( createConnections() ) {
<a href="qsqlcursor.html">QSqlCursor</a> cur( "staff" ); // Specify the table/view name
<a name="x2178"></a> cur.<a href="qsqlcursor.html#select">select</a>(); // We'll retrieve every record
while ( cur.<a href="qsqlquery.html#next">next</a>() ) {
<a name="x2179"></a> <a href="qapplication.html#qDebug">qDebug</a>( cur.<a href="qsqlquery.html#value">value</a>( "id" ).toString() + ": " +
cur.<a href="qsqlquery.html#value">value</a>( "surname" ).toString() + " " +
cur.<a href="qsqlquery.html#value">value</a>( "salary" ).toString() );
}
}
return 0;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-retrieve2-main-cpp.html">sql/overview/retrieve2/main.cpp</a>
</em></p>
</blockquote><p> We create the <a href="qsqlcursor.html">QSqlCursor</a> object, specifying the table or view to use.
If we need to use a database other than the default we can specify it
in the <a href="qsqlcursor.html">QSqlCursor</a> constructor.
<p> The SQL executed by the cur.select() call is
<p> <pre>
SELECT staff.id, staff.forename, staff.surname, staff.salary, staff.statusid FROM staff
</pre>
<p> Next, we iterate through the records returned by this select statement
using cur.next(). Field values are retrieved in in a similar way to
<a href="qsqlquery.html">QSqlQuery</a>, except that we pass field names rather than numeric indexes
to value() and setValue().
<p> <a name="Sorting_Data"></a>
<h4> Sorting and Filtering Records
</h4>
<a name="7-1-1"></a><p> To specify a subset of records to retrieve we can pass filtering
criteria to the select() function. Each record that is returned will
meet the criteria of the filter (the filter corresponds to the SQL
statement's <tt>WHERE</tt> clause).
<p> <pre>
cur.select( "id > 100" );
</pre>
<p> This select() call will execute the SQL
<pre>
SELECT staff.id, staff.forename, staff.surname, staff.salary, staff.statusid
FROM staff WHERE staff.id > 100
</pre>
<p> This will retrieve only those staff whose <tt>id</tt> is greater than 100.
<p> In addition to retrieving selected records we often want to specify a
sort order for the returned records. This is achieved by creating a <a href="qsqlindex.html">QSqlIndex</a> object which contains the names of the field(s) we wish to
sort by and pass this object to the select() call.
<p> <pre>
<a href="qsqlcursor.html">QSqlCursor</a> cur( "staff" );
<a href="qsqlindex.html">QSqlIndex</a> nameIndex = cur.<a href="qsqlcursor.html#index">index</a>( "surname" );
cur.<a href="qsqlcursor.html#select">select</a>( nameIndex );
</pre>
<p> Here we create a <a href="qsqlindex.html">QSqlIndex</a> object with one field, "surname". When
we call the select() function we pass the index object, which
specifies that the records should be returned sorted by
staff.surname. Each field in the index object is used in the ORDER BY
clause of the select statement. The SQL executed here is
<pre>
SELECT staff.id, staff.forename, staff.surname, staff.salary, staff.statusid
FROM staff ORDER BY staff.surname ASC
</pre>
<p> Combining the retrieval of a subset of records and ordering the results
is straightforward.
<p> <pre>
cur.select( "staff.surname LIKE 'A%'", nameIndex );
</pre>
<p> We pass in a filter string (the <tt>WHERE</tt> clause), and the <a href="qsqlindex.html">QSqlIndex</a>
object to sort by (the <tt>ORDER BY</tt> clause). This produces
<p> <pre>
SELECT staff.id, staff.forename, staff.surname, staff.salary, staff.statusid
FROM staff WHERE staff.surname LIKE 'A%' ORDER BY staff.surname ASC
</pre>
<p> To sort by more than one field, an index can be created which contains
multiple fields. Ascending and descending order can be set using
<a href="qsqlindex.html#setDescending">QSqlIndex::setDescending</a>(); the default is ascending.
<p>
<pre> <a href="qsqlcursor.html">QSqlCursor</a> cur( "staff" );
<a href="qstringlist.html">QStringList</a> fields = QStringList() << "surname" << "forename";
<a name="x2181"></a> <a href="qsqlindex.html">QSqlIndex</a> order = cur.<a href="qsqlcursor.html#index">index</a>( fields );
<a name="x2182"></a> cur.<a href="qsqlcursor.html#select">select</a>( order );
<a name="x2183"></a> while ( cur.<a href="qsqlquery.html#next">next</a>() ) {
</pre><blockquote><p align="center"><em> From <a href="sql-overview-order1-main-cpp.html">sql/overview/order1/main.cpp</a>
</em></p>
</blockquote><p> Here we create a string list containing the fields we wish to sort by,
in the order they are to be used. Then we create a <a href="qsqlindex.html">QSqlIndex</a> object
based on these fields, finally executing the select() call using this
index. This executes
<pre>
SELECT staff.id, staff.forename, staff.surname, staff.salary, staff.statusid
FROM staff ORDER BY staff.surname ASC, staff.forename ASC
</pre>
<p> If we need to retrieve records with fields that match specific criteria we
can create a filter based on an index.
<p>
<pre> <a href="qsqlcursor.html">QSqlCursor</a> cur( "staff" );
<a href="qstringlist.html">QStringList</a> fields = QStringList() << "id" << "forename";
<a name="x2184"></a> <a href="qsqlindex.html">QSqlIndex</a> order = cur.<a href="qsqlcursor.html#index">index</a>( fields );
<a href="qsqlindex.html">QSqlIndex</a> filter = cur.<a href="qsqlcursor.html#index">index</a>( "surname" );
<a name="x2186"></a> cur.<a href="qsqlrecord.html#setValue">setValue</a>( "surname", "Bloggs" );
<a name="x2185"></a> cur.<a href="qsqlcursor.html#select">select</a>( filter, order );
while ( cur.<a href="qsqlquery.html#next">next</a>() ) {
</pre><blockquote><p align="center"><em> From <a href="sql-overview-order2-main-cpp.html">sql/overview/order2/main.cpp</a>
</em></p>
</blockquote><p> This executes
<pre>
SELECT staff.id, staff.forename, staff.surname, staff.salary, staff.statusid
FROM staff WHERE staff.surname='Bloggs' ORDER BY staff.id ASC, staff.forename ASC
</pre>
<p> The "order" <a href="qsqlindex.html">QSqlIndex</a> contains two fields, "id" and "forename"
which are used to order the results. The "filter" <a href="qsqlindex.html">QSqlIndex</a>
contains a single field, "surname". When an index is passed as a
filter to the select() function, for each field in the filter, a
<em>fieldname=value</em> subclause is created where the value
is taken from the current cursor's value for that field. We use
setValue() to ensure that the value used is the one we want.
<p> <a name="Extracting_Data"></a>
<h4> Extracting Data
</h4>
<a name="7-1-2"></a><p>
<pre> <a href="qsqlcursor.html">QSqlCursor</a> cur( "creditors" );
<a href="qstringlist.html">QStringList</a> orderFields = QStringList() << "surname" << "forename";
<a name="x2188"></a> <a href="qsqlindex.html">QSqlIndex</a> order = cur.<a href="qsqlcursor.html#index">index</a>( orderFields );
<a href="qstringlist.html">QStringList</a> filterFields = QStringList() << "surname" << "city";
<a href="qsqlindex.html">QSqlIndex</a> filter = cur.<a href="qsqlcursor.html#index">index</a>( filterFields );
<a name="x2190"></a> cur.<a href="qsqlrecord.html#setValue">setValue</a>( "surname", "Chirac" );
cur.<a href="qsqlrecord.html#setValue">setValue</a>( "city", "Paris" );
<a name="x2189"></a> cur.<a href="qsqlcursor.html#select">select</a>( filter, order );
while ( cur.<a href="qsqlquery.html#next">next</a>() ) {
<a name="x2191"></a> int id = cur.<a href="qsqlquery.html#value">value</a>( "id" ).toInt();
<a href="qstring.html">QString</a> name = cur.<a href="qsqlquery.html#value">value</a>( "forename" ).toString() + " " +
cur.<a href="qsqlquery.html#value">value</a>( "surname" ).toString();
<a name="x2193"></a> <a href="qapplication.html#qDebug">qDebug</a>( QString::<a href="qstring.html#number">number</a>( id ) + ": " + name );
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-extract-main-cpp.html">sql/overview/extract/main.cpp</a>
</em></p>
</blockquote><p> In this example we begin by creating a cursor on the creditors table.
We create two <a href="qsqlindex.html">QSqlIndex</a> objects. The first, "order", is created
from the "orderFields" string list. The second, "filter", is created
from the "filterFields" string list. We set the values of the two
fields used in the filter, "surname" and "city", to the values we're
interested in. Now we call select() which generates and executes the
following SQL:
<pre>
SELECT creditors.city, creditors.surname, creditors.forename, creditors.id
FROM creditors
WHERE creditors.surname = 'Chirac' AND creditors.city = 'Paris'
ORDER BY creditors.surname ASC, creditors.forename ASC
</pre>
The filter fields are used in the <tt>WHERE</tt> clause. Their values are
taken from the cursor's current values for those fields; we set these
values ourselves with the setValue() calls. The order fields are used
in the <tt>ORDER BY</tt> clause.
<p> Now we iterate through each matching record (if any). We retrieve the
contents of the id, forename and surname fields and pass them on to
some processing function, in this example a simple <a href="qapplication.html#qDebug">qDebug</a>() call.
<p> <a name="Manipulating_Records"></a>
<h3> Manipulating Records
</h3>
<a name="7-2"></a><p> Records can be inserted, updated or deleted in a table or view using a
<a href="qsqlcursor.html">QSqlCursor</a> providing that the table or view has a primary index
that uniquely distinguishes each record. If this is not the case a <a href="qsqlquery.html">QSqlQuery</a> must be used instead. (Note that not all databases support
editable views.)
<p> Each cursor has an internal 'edit buffer' which is used by all the
edit operations (insert, update and delete). The editing process is
the same for each operation: acquire a pointer to the relevant buffer;
call setValue() to <a href="primes.html#prime">prime</a> the buffer with the values you want; call
insert() or update() or del() to perform the desired operation. For
example, when inserting a record using a cursor, you call
primeInsert() to get a pointer to the edit buffer and then call
setValue() on this buffer to set each field's value. Then you call
QSQlCursor::insert() to insert the contents of the edit buffer into
the database. Similarly, when updating (or deleting) a record, the
values of the fields in the edit buffer are used to update (or delete)
the record in the database. The 'edit buffer' is unaffected by any
<a href="#Navigating_Result_Sets">cursor navigation</a> functions.
Note that if you pass a string value to setValue() any single quotes
will be escaped (turned into a pair of single quotes) since a single
quote is a special character in SQL.
<p> The primeInsert(), primeUpdate() and primeDelete() methods all return
a pointer to the internal edit buffer. Each method can potentially
perform different operations on the edit buffer before returning it.
By default, <a href="qsqlcursor.html#primeInsert">QSqlCursor::primeInsert</a>() clears all the field values in
the edit buffer (see <a href="qsqlrecord.html#clearValues">QSqlRecord::clearValues</a>()). Both <a href="qsqlcursor.html#primeUpdate">QSqlCursor::primeUpdate</a>() and <a href="qsqlcursor.html#primeDelete">QSqlCursor::primeDelete</a>() initialize the
edit buffer with the current contents of the cursor before returning
it. All three of these functions are virtual, so you can redefine the
behavior (for example, reimplementing primeInsert() to auto-number
fields in the edit buffer). Data-aware user-interface controls emit
signals, e.g. primeInsert(), that you can connect to; these pass a
pointer to the appropriate buffer so subclassing may not be necessary.
See <a href="#Subclassing_QSqlCursor">subclassing QSqlCursor</a> for
more information on subclassing; see the <a href="designer-manual.html">Qt
Designer</a> manual for more on connecting to the primeInsert()
signal.
<p> When insert(), update() or del() is called on a cursor, it will be
invalidated and will no longer be positioned on a valid record. If you
need to move to another record after performing an insert(), update()
or del() you must make a fresh select() call. This ensures that
changes to the database are accurately reflected in the cursor.
<p> <a name="Inserting_Records"></a>
<h4> Inserting Records
</h4>
<a name="7-2-1"></a><p>
<pre> <a href="qsqlcursor.html">QSqlCursor</a> cur( "prices" );
<a href="qstringlist.html">QStringList</a> names = QStringList() <<
"Screwdriver" << "Hammer" << "Wrench" << "Saw";
int id = 20;
<a name="x2197"></a> for ( QStringList::Iterator name = names.<a href="qvaluelist.html#begin">begin</a>();
<a name="x2198"></a> name != names.<a href="qvaluelist.html#end">end</a>(); ++name ) {
<a name="x2195"></a> <a href="qsqlrecord.html">QSqlRecord</a> *buffer = cur.<a href="qsqlcursor.html#primeInsert">primeInsert</a>();
<a name="x2196"></a> buffer-><a href="qsqlrecord.html#setValue">setValue</a>( "id", id );
buffer-><a href="qsqlrecord.html#setValue">setValue</a>( "name", *name );
buffer-><a href="qsqlrecord.html#setValue">setValue</a>( "price", 100.0 + (double)id );
<a name="x2194"></a> count += cur.<a href="qsqlcursor.html#insert">insert</a>();
id++;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-insert-main-cpp.html">sql/overview/insert/main.cpp</a>
</em></p>
</blockquote><p> In this example we create a cursor on the "prices" table. Next we
create a list of product names which we iterate over. For each
iteration we call the cursor's primeInsert() method. This method
returns a pointer to a <a href="qsqlrecord.html">QSqlRecord</a> buffer in which all the fields
are set to <tt>NULL</tt>. (Note that <a href="qsqlcursor.html#primeInsert">QSqlCursor::primeInsert</a>() is virtual,
and can be customized by derived classes. See <a href="qsqlcursor.html">QSqlCursor</a>). Next we
call setValue() for each field that requires a value. Finally we call
insert() to insert the record. The insert() call returns the number of
rows inserted.
<p> We obtained a pointer to a <a href="qsqlrecord.html">QSqlRecord</a> object from the primeInsert()
call. <a href="qsqlrecord.html">QSqlRecord</a> objects can hold the data for a single record plus some
meta-data about the record. In practice most interaction with a
QSqlRecord consists of simple value() and setValue() calls as shown in
this and the following example.
<p> <a name="Updating_Records"></a>
<h4> Updating Records
</h4>
<a name="7-2-2"></a><p>
<pre> <a href="qsqlcursor.html">QSqlCursor</a> cur( "prices" );
<a name="x2200"></a> cur.<a href="qsqlcursor.html#select">select</a>( "id=202" );
if ( cur.<a href="qsqlquery.html#next">next</a>() ) {
<a name="x2199"></a> <a href="qsqlrecord.html">QSqlRecord</a> *buffer = cur.<a href="qsqlcursor.html#primeUpdate">primeUpdate</a>();
<a name="x2204"></a> double price = buffer-><a href="qsqlrecord.html#value">value</a>( "price" ).toDouble();
double newprice = price * 1.05;
<a name="x2203"></a> buffer-><a href="qsqlrecord.html#setValue">setValue</a>( "price", newprice );
<a name="x2201"></a> cur.<a href="qsqlcursor.html#update">update</a>();
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-update-main-cpp.html">sql/overview/update/main.cpp</a>
</em></p>
</blockquote><p> This example begins with the creation of a cursor over the prices table.
We select the record we wish to update with the select() call and
move to it with the next() call. We call primeUpdate() to get a <a href="qsqlrecord.html">QSqlRecord</a> pointer to a buffer which is populated with the contents of
the current record. We retrieve the value of the price field, calculate
a new price, and set the the price field to the newly calculated value.
Finally we call update() to update the record. The update() call returns
the number of rows updated.
<p> If many identical updates need to be performed, for example increasing
the price of every item in the price list, using a single SQL statement
with <a href="qsqlquery.html">QSqlQuery</a> is more efficient, e.g.
<p> <pre>
<a href="qsqlquery.html">QSqlQuery</a> query( "UPDATE prices SET price = price * 1.05" );
</pre>
<p> <a name="Deleting_Records"></a>
<h4> Deleting Records
</h4>
<a name="7-2-3"></a><p>
<pre> <a href="qsqlcursor.html">QSqlCursor</a> cur( "prices" );
<a name="x2207"></a> cur.<a href="qsqlcursor.html#select">select</a>( "id=999" );
<a name="x2208"></a> if ( cur.<a href="qsqlquery.html#next">next</a>() ) {
<a name="x2206"></a> cur.<a href="qsqlcursor.html#primeDelete">primeDelete</a>();
<a name="x2205"></a> cur.<a href="qsqlcursor.html#del">del</a>();
</pre><blockquote><p align="center"><em> From <a href="sql-overview-delete-main-cpp.html">sql/overview/delete/main.cpp</a>
</em></p>
</blockquote><p> To delete records, select the record to be deleted and navigate to it.
Then call primeDelete() to populate the cursor with the primary key
of the selected record, (in this example, the <tt>prices.id</tt> field), and
then call <a href="qsqlcursor.html#del">QSqlCursor::del</a>() to delete it.
<p> As with update(), if multiple deletions need to be made with some common
criteria it is more efficient to do so using a single SQL statement,
e.g.
<p> <pre>
<a href="qsqlquery.html">QSqlQuery</a> query( "DELETE FROM prices WHERE id >= 2450 AND id <= 2500" );
</pre>
<p> <a name="Data-Aware_Widgets"></a>
<h2> Data-Aware Widgets
</h2>
<a name="8"></a><p> Data-Aware Widgets provide a simple yet powerful means of connecting
databases to Qt user interfaces. The easiest way of creating and
manipulating data-aware widgets is with <a href="designer-manual.html">Qt
Designer</a>. For those who prefer a purely programmatic approach
the following examples and explanations provide an introduction. Note
that the "Creating Database Applications" chapter of the <a href="designer-manual.html">Qt Designer</a> manual and its accompanying
examples provides additional information.
<p> <a name="Data-Aware_Tables"></a>
<h3> Data-Aware Tables
</h3>
<a name="8-1"></a><p>
<pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qsqldatabase-h.html">qsqldatabase.h</a>>
#include <<a href="qsqlcursor-h.html">qsqlcursor.h</a>>
#include <<a href="qdatatable-h.html">qdatatable.h</a>>
#include "../connection.h"
int main( int argc, char *argv[] )
{
<a href="qapplication.html">QApplication</a> app( argc, argv );
if ( createConnections() ) {
<a href="qsqlcursor.html">QSqlCursor</a> staffCursor( "staff" );
<a href="qdatatable.html">QDataTable</a> *staffTable = new <a href="qdatatable.html">QDataTable</a>( &staffCursor, TRUE );
app.<a href="qapplication.html#setMainWidget">setMainWidget</a>( staffTable );
<a name="x2211"></a> staffTable-><a href="qdatatable.html#refresh">refresh</a>();
staffTable-><a href="qwidget.html#show">show</a>();
return app.<a href="qapplication.html#exec">exec</a>();
}
return 0;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-table1-main-cpp.html">sql/overview/table1/main.cpp</a>
</em></p>
</blockquote><p> Data-Aware tables require the <a href="qdatatable-h.html">qdatatable.h</a> and <a href="qsqlcursor-h.html">qsqlcursor.h</a> header
files. We create our application object, call createConnections() and
create the cursor. We create the <a href="qdatatable.html">QDataTable</a> passing it a pointer to
the cursor, and set the autoPopulate flag to TRUE. Next we make our <a href="qdatatable.html">QDataTable</a> the main widget and call refresh() to populate it with data
and call show() to make it visible.
<p> The autoPopulate flag tells the <a href="qdatatable.html">QDataTable</a> whether or nor it should
create columns based on the cursor. autoPopulate does not affect the
loading of data into the table; that is achieved by the refresh()
function.
<p>
<pre> <a href="qsqlcursor.html">QSqlCursor</a> staffCursor( "staff" );
<a href="qdatatable.html">QDataTable</a> *staffTable = new <a href="qdatatable.html">QDataTable</a>( &staffCursor );
app.<a href="qapplication.html#setMainWidget">setMainWidget</a>( staffTable );
<a name="x2214"></a> staffTable-><a href="qdatatable.html#addColumn">addColumn</a>( "forename", "Forename" );
staffTable-><a href="qdatatable.html#addColumn">addColumn</a>( "surname", "Surname" );
staffTable-><a href="qdatatable.html#addColumn">addColumn</a>( "salary", "Annual Salary" );
<a href="qstringlist.html">QStringList</a> order = QStringList() << "surname" << "forename";
<a name="x2216"></a> staffTable-><a href="qdatatable.html#setSort">setSort</a>( order );
<a name="x2215"></a> staffTable-><a href="qdatatable.html#refresh">refresh</a>();
staffTable-><a href="qwidget.html#show">show</a>();
</pre><blockquote><p align="center"><em> From <a href="sql-overview-table2-main-cpp.html">sql/overview/table2/main.cpp</a>
</em></p>
</blockquote><p> We create an empty <a href="qdatatable.html">QDataTable</a> which we make into our main widget and
then we manually add the columns we want in the order we wish them to
appear. For each column we specify the field name and optionally a
display label.
<p> We have also opted to sort the rows in the table; this could also have
been achieved by applying the sort to the cursor itself.
<p> Once everything is set up we call refresh() to load the data from the
database and show() to make the widget visible.
<p> QDataTables only retrieve visible rows which (depending on the driver)
allows even large tables to be displayed very quickly with minimal
memory cost.
<p> <a name="Creating_Forms"></a>
<h3> Creating Data-Aware Forms
</h3>
<a name="8-2"></a><p> Creating data-aware forms is more involved than using data-aware
tables because we must take care of each field individually. Most of
the code below can be automatically generated by <a href="designer-manual.html">Qt Designer</a>. See the <a href="designer-manual.html">Qt Designer</a> manual for more details.
<p> <a name="Displaying_a_Record"></a>
<h4> Displaying a Record
</h4>
<a name="8-2-1"></a><p>
<pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qdialog-h.html">qdialog.h</a>>
#include <<a href="qlabel-h.html">qlabel.h</a>>
#include <<a href="qlayout-h.html">qlayout.h</a>>
#include <<a href="qlineedit-h.html">qlineedit.h</a>>
#include <<a href="qsqldatabase-h.html">qsqldatabase.h</a>>
#include <<a href="qsqlcursor-h.html">qsqlcursor.h</a>>
#include <<a href="qsqlform-h.html">qsqlform.h</a>>
#include "../connection.h"
class FormDialog : public <a href="qdialog.html">QDialog</a>
{
public:
FormDialog();
};
FormDialog::FormDialog()
{
<a href="qlabel.html">QLabel</a> *forenameLabel = new <a href="qlabel.html">QLabel</a>( "Forename:", this );
<a href="qlabel.html">QLabel</a> *forenameDisplay = new <a href="qlabel.html">QLabel</a>( this );
<a href="qlabel.html">QLabel</a> *surnameLabel = new <a href="qlabel.html">QLabel</a>( "Surname:", this );
<a href="qlabel.html">QLabel</a> *surnameDisplay = new <a href="qlabel.html">QLabel</a>( this );
<a href="qlabel.html">QLabel</a> *salaryLabel = new <a href="qlabel.html">QLabel</a>( "Salary:", this );
<a href="qlineedit.html">QLineEdit</a> *salaryEdit = new <a href="qlineedit.html">QLineEdit</a>( this );
<a href="qgridlayout.html">QGridLayout</a> *grid = new <a href="qgridlayout.html">QGridLayout</a>( this );
<a name="x2221"></a> grid-><a href="qgridlayout.html#addWidget">addWidget</a>( forenameLabel, 0, 0 );
grid-><a href="qgridlayout.html#addWidget">addWidget</a>( forenameDisplay, 0, 1 );
grid-><a href="qgridlayout.html#addWidget">addWidget</a>( surnameLabel, 1, 0 );
grid-><a href="qgridlayout.html#addWidget">addWidget</a>( surnameDisplay, 1, 1 );
grid-><a href="qgridlayout.html#addWidget">addWidget</a>( salaryLabel, 2, 0 );
grid-><a href="qgridlayout.html#addWidget">addWidget</a>( salaryEdit, 2, 1 );
<a name="x2222"></a> grid-><a href="qlayout.html#activate">activate</a>();
<a href="qsqlcursor.html">QSqlCursor</a> staffCursor( "staff" );
staffCursor.<a href="qsqlcursor.html#select">select</a>();
staffCursor.<a href="qsqlquery.html#next">next</a>();
<a href="qsqlform.html">QSqlForm</a> sqlForm( this );
<a name="x2227"></a><a name="x2223"></a> sqlForm.<a href="qsqlform.html#setRecord">setRecord</a>( staffCursor.<a href="qsqlcursor.html#primeUpdate">primeUpdate</a>() );
<a name="x2225"></a> sqlForm.<a href="qsqlform.html#insert">insert</a>( forenameDisplay, "forename" );
sqlForm.<a href="qsqlform.html#insert">insert</a>( surnameDisplay, "surname" );
sqlForm.<a href="qsqlform.html#insert">insert</a>( salaryEdit, "salary" );
<a name="x2226"></a> sqlForm.<a href="qsqlform.html#readFields">readFields</a>();
}
int main( int argc, char *argv[] )
{
<a href="qapplication.html">QApplication</a> app( argc, argv );
if ( ! createConnections() ) return 1;
FormDialog *formDialog = new FormDialog();
<a name="x2220"></a> formDialog-><a href="qdialog.html#show">show</a>();
app.<a href="qapplication.html#setMainWidget">setMainWidget</a>( formDialog );
return app.<a href="qapplication.html#exec">exec</a>();
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-form1-main-cpp.html">sql/overview/form1/main.cpp</a>
</em></p>
</blockquote><p> We include the header files for the widgets that we need. We also
include <a href="qsqldatabase-h.html">qsqldatabase.h</a> and <a href="qsqlcursor-h.html">qsqlcursor.h</a> as usual, but we now add
<a href="qsqlform-h.html">qsqlform.h</a>.
<p> The form will be presented as a dialog so we subclass <a href="qdialog.html">QDialog</a> with
our own FormDialog class. We use a <a href="qlineedit.html">QLineEdit</a> for the salary so that
the user can change it. All the widgets are laid out using a grid.
<p> We create a cursor on the staff table, select all records and move to
the first record.
<p> Now we create a <a href="qsqlform.html">QSqlForm</a> object and set the <a href="qsqlform.html">QSqlForm</a>'s record buffer
to the cursor's update buffer. For each widget that we wish to make
data-aware we insert a pointer to the widget and the associated field
name into the <a href="qsqlform.html">QSqlForm</a>. Finally we call readFields() to populate the
widgets with data from the database via the cursor's buffer.
<p> <a name="Displaying_a_Record_in_a_DataForm"></a>
<h4> Displaying a Record in a Data Form
</h4>
<a name="8-2-2"></a><p> <a href="qdataview.html">QDataView</a> is a Widget that can hold a read-only <a href="qsqlform.html">QSqlForm</a>. In
addition to <a href="qsqlform.html">QSqlForm</a> it offers the slot refresh( <a href="qsqlrecord.html">QSqlRecord</a> * ) so it
can easily be linked together with a <a href="qdatatable.html">QDataTable</a> to display a detailed
view of a record:
<p> <pre>
connect( myDataTable, SIGNAL( currentChanged( <a href="qsqlrecord.html">QSqlRecord</a>* ) ),
myDataView, SLOT( refresh( <a href="qsqlrecord.html">QSqlRecord</a>* ) ) );
</pre>
<p> <a name="Editing_a_Record"></a>
<h4> Editing a Record
</h4>
<a name="8-2-3"></a><p> This example is similar to the previous one so we will focus on the
differences.
<p>
<pre> class FormDialog : public <a href="qdialog.html">QDialog</a>
{
<a href="metaobjects.html#Q_OBJECT">Q_OBJECT</a>
public:
FormDialog();
~FormDialog();
public slots:
void save();
private:
<a href="qsqlcursor.html">QSqlCursor</a> staffCursor;
<a href="qsqlform.html">QSqlForm</a> *sqlForm;
<a href="qsqlindex.html">QSqlIndex</a> idIndex;
};
</pre><blockquote><p align="center"><em> From <a href="sql-overview-form2-main-h.html">sql/overview/form2/main.h</a>
</em></p>
</blockquote><p> The save slot will be used for a button that the user can press to
confirm their update. We also hold pointers to the <a href="qsqlcursor.html">QSqlCursor</a> and the
<a href="qsqlform.html">QSqlForm</a> since they will need to be accessed outside the constructor.
<p>
<pre> staffCursor.setTrimmed( "forename", TRUE );
staffCursor.setTrimmed( "surname", TRUE );
</pre>
<p> We call setTrimmed() on the text fields so that any spaces used to
right pad the fields are removed when the fields are retrieved.
<p> Properties that we might wish to apply to fields, such as alignment
and validation are achieved in the conventional way, for example, by
calling <a href="qlineedit.html#setAlignment">QLineEdit::setAlignment</a>() and <a href="qlineedit.html#setValidator">QLineEdit::setValidator</a>().
<p> <pre> <a href="qlineedit.html">QLineEdit</a> *forenameEdit = new <a href="qlineedit.html">QLineEdit</a>( this );
</pre>
<p> <pre> <a href="qpushbutton.html">QPushButton</a> *saveButton = new <a href="qpushbutton.html">QPushButton</a>( "&Save", this );
<a href="qobject.html#connect">connect</a>( saveButton, SIGNAL(<a href="qbutton.html#clicked">clicked</a>()), this, SLOT(save()) );
</pre>
<p> The FormDialog constructor is similar to the one in the previous
example. We have changed the forename and surname widgets to
<a href="qlineedit.html">QLineEdit</a>s to make them editable and have added a <a href="qpushbutton.html">QPushButton</a>
the user can click to save their updates.
<p> <pre> <a name="x2230"></a> grid-><a href="qgridlayout.html#addWidget">addWidget</a>( saveButton, 3, 0 );
</pre>
<p> We add an extra row to the grid containing the save button.
<p> <pre> idIndex = staffCursor.index( "id" );
staffCursor.select( idIndex );
staffCursor.first();
</pre>
<p> We create a <a href="qsqlindex.html">QSqlIndex</a> object and then execute a select() using the
index. We then move to the first record in the result set.
<p> <pre> sqlForm = new <a href="qsqlform.html">QSqlForm</a>( this );
<a name="x2233"></a> sqlForm-><a href="qsqlform.html#setRecord">setRecord</a>( staffCursor.primeUpdate() );
</pre>
<p> We create a new <a href="qsqlform.html">QSqlForm</a> object and set it's record buffer to the
cursor's update buffer.
<p> <pre> <a name="x2231"></a> sqlForm-><a href="qsqlform.html#insert">insert</a>( forenameEdit, "forename" );
sqlForm-><a href="qsqlform.html#insert">insert</a>( surnameEdit, "surname" );
sqlForm-><a href="qsqlform.html#insert">insert</a>( salaryEdit, "salary" );
<a name="x2232"></a> sqlForm-><a href="qsqlform.html#readFields">readFields</a>();
</pre>
<p> Now we link the buffer's fields to the <a href="qlineedit.html">QLineEdit</a> controls. (In the
previous example we linked the cursor's fields.) The edit controls are
populated by the readFields() call as before.
<p> <pre> FormDialog::~FormDialog()
{
}
</pre>
<p> In the destructor we don't have to worry about the widgets or QSqlForm
since they are children of the form and will be deleted by Qt at the
right time.
<p> <pre> void FormDialog::save()
{
<a name="x2234"></a> sqlForm-><a href="qsqlform.html#writeFields">writeFields</a>();
staffCursor.update();
staffCursor.select( idIndex );
staffCursor.first();
}
</pre>
<p> Finally we add the save functionality for when the user presses the
save button. We write back the data from the widgets to the <a href="qsqlrecord.html">QSqlRecord</a> buffer with the writeFields() call. Then we update the
database with the updated version of the record with the cursor's
update() function. At this point the cursor is no longer positioned at
a valid record so we reissue the select() call using our <a href="qsqlindex.html">QSqlIndex</a>
and move to the first record.
<p> <a href="qdatabrowser.html">QDataBrowser</a> and <a href="qdataview.html">QDataView</a> are widgets which provide a great deal of
the above functionality. <a href="qdatabrowser.html">QDataBrowser</a> provides a data form which
allows editing of and navigation through a cursor's records. <a href="qdataview.html">QDataView</a> provides a read only form for data in a cursor or database
record. See the class documentation or the <a href="designer-manual.html">Qt Designer</a> manual for more information on using these
widgets.
<p> Link to <a href="sql.html">sql/overview/form2/main.cpp</a>
<p> <a name="Custom_Editor_Widgets"></a>
<h3> Custom Editor Widgets
</h3>
<a name="8-3"></a><p> <a href="qsqlform.html">QSqlForm</a> uses <a href="qsqlpropertymap.html">QSqlPropertyMap</a> to handle the transfer of data between
widgets and database fields. Custom widgets can also be used in a form
by installing a property map that contains information about the
properties of the custom widget which should be used to transfer the
data.
<p> This example is based on the form2 example in the previous section so
we will only cover the differences here. The full source is in <a href="sql-overview-custom1-main-h.html">sql/overview/custom1/main.h</a> and <a href="sql-overview-custom1-main-cpp.html">sql/overview/custom1/main.cpp</a>
<p>
<pre> class CustomEdit : public <a href="qlineedit.html">QLineEdit</a>
{
Q_OBJECT
Q_PROPERTY( QString upperLine READ upperLine WRITE setUpperLine )
public:
CustomEdit( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
<a href="qstring.html">QString</a> upperLine() const;
void setUpperLine( const <a href="qstring.html">QString</a> &line );
public slots:
void changed( const <a href="qstring.html">QString</a> &line );
private:
<a href="qstring.html">QString</a> upperLineText;
};
</pre>
<p> We've created a simple subclass of <a href="qlineedit.html">QLineEdit</a> and added a property,
upperLineText, which will hold an uppercase version of the text. We
also created a slot, changed().
<p> <pre> <a href="qsqlpropertymap.html">QSqlPropertyMap</a> *propMap;
</pre>
<p> We will be using a property map so we add a pointer to a property map
to our FormDialog's private data.
<p>
<pre> CustomEdit::CustomEdit( <a href="qwidget.html">QWidget</a> *parent, const char *name ) :
<a href="qlineedit.html">QLineEdit</a>( parent, name )
{
<a href="qobject.html#connect">connect</a>( this, SIGNAL(<a href="qlineedit.html#textChanged">textChanged</a>(const <a href="qstring.html">QString</a> &)),
this, SLOT(changed(const <a href="qstring.html">QString</a> &)) );
}
</pre>
<p> In the CustomEdit constructor we use the QLineEdit constructor and add
a connection between the textChanged signal and our own changed slot.
<p> <pre> void CustomEdit::changed( const <a href="qstring.html">QString</a> &line )
{
setUpperLine( line );
}
</pre>
<p> The changed() slot calls our setUpperLine() function.
<p> <pre> void CustomEdit::setUpperLine( const <a href="qstring.html">QString</a> &line )
{
<a name="x2240"></a> upperLineText = line.<a href="qstring.html#upper">upper</a>();
setText( upperLineText );
}
</pre>
<p> The setUpperLine() function places an uppercase copy of the text in the
upperLineText buffer and then sets the text of the widget to this text.
<p> Our CustomEdit class ensures that the text entered is always uppercase
and provides a property that can be used with a property map to link
CustomEdit instances directly to database fields.
<p> <pre> CustomEdit *forenameEdit = new CustomEdit( this );
</pre>
<p> <pre> CustomEdit *surnameEdit = new CustomEdit( this );
</pre>
<p> We use the same FormDialog as we did before, but this time replace two
of the <a href="qlineedit.html">QLineEdit</a> widgets with our own CustomEdit widgets.
<p> Laying out the grid and setting up the cursor is the same as before.
<p> <pre> propMap = new <a href="qsqlpropertymap.html">QSqlPropertyMap</a>;
<a name="x2239"></a><a name="x2235"></a> propMap-><a href="qsqlpropertymap.html#insert">insert</a>( forenameEdit-><a href="qobject.html#className">className</a>(), "upperLine" );
</pre>
<p> We create a new property map on the heap and register our CustomEdit
class and its upperLine property with the property map.
<p> <pre> sqlForm = new <a href="qsqlform.html">QSqlForm</a>( this );
<a name="x2238"></a><a name="x2236"></a> sqlForm-><a href="qsqlform.html#setRecord">setRecord</a>( staffCursor-><a href="qsqlcursor.html#primeUpdate">primeUpdate</a>() );
<a name="x2237"></a> sqlForm-><a href="qsqlform.html#installPropertyMap">installPropertyMap</a>( propMap );
</pre>
<p> The final change is to install the property map into the <a href="qsqlform.html">QSqlForm</a> once
the QSqlForm has been created. This passes responsibility for the
property map's memory to QSqlForm which itself is owned by the
FormDialog, so Qt will delete them at the right time.
<p> The behaviour of this example is identical to the previous one except
that the forename and surname fields will be uppercase since they use
our CustomEdit widget.
<p> <a name="Custom_Editor_Widgets_for_Tables"></a>
<h4> Custom Editor Widgets for Tables
</h4>
<a name="8-3-1"></a><p> We must reimpliment <a href="qsqleditorfactory.html">QSqlEditorFactory</a> to use custom editor widgets in
tables. In the following example we will create a custom editor based
on <a href="qcombobox.html">QComboBox</a> and a QSqlEditorFactory subclass to show how a <a href="qdatatable.html">QDataTable</a>
can use a custom editor.
<p>
<pre> class StatusPicker : public <a href="qcombobox.html">QComboBox</a>
{
Q_OBJECT
Q_PROPERTY( int statusid READ statusId WRITE setStatusId )
public:
StatusPicker( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
int statusId() const;
void setStatusId( int id );
private:
<a href="qmap.html">QMap</a>< int, int > index2id;
};
</pre><blockquote><p align="center"><em> From <a href="sql-overview-table3-main-h.html">sql/overview/table3/main.h</a>
</em></p>
</blockquote><p> We create a property, statusid, and define our READ and WRITE methods
for it. The statusid's in the status table will probably be different
from the combobox's indexes so we create a <a href="qmap.html">QMap</a> to map combobox indexes
to/from the statusids that we will list in the combobox.
<p> <pre> class CustomSqlEditorFactory : public <a href="qsqleditorfactory.html">QSqlEditorFactory</a>
{
Q_OBJECT
public:
<a href="qwidget.html">QWidget</a> *createEditor( <a href="qwidget.html">QWidget</a> *parent, const <a href="qsqlfield.html">QSqlField</a> *field );
};
</pre>
<p> We also need to subclass <a href="qsqleditorfactory.html">QSqlEditorFactory</a> declaring a createEditor()
function since that is the only function we need to reimplement.
<p>
<pre> StatusPicker::StatusPicker( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qcombobox.html">QComboBox</a>( parent, name )
{
<a href="qsqlcursor.html">QSqlCursor</a> cur( "status" );
<a name="x2242"></a><a name="x2241"></a> cur.<a href="qsqlcursor.html#select">select</a>( cur.<a href="qsqlcursor.html#index">index</a>( "name" ) );
int i = 0;
while ( cur.<a href="qsqlquery.html#next">next</a>() ) {
<a name="x2243"></a> <a href="qcombobox.html#insertItem">insertItem</a>( cur.<a href="qsqlquery.html#value">value</a>( "name" ).toString(), i );
index2id[i] = cur.<a href="qsqlquery.html#value">value</a>( "id" ).toInt();
i++;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-table3-main-cpp.html">sql/overview/table3/main.cpp</a>
</em></p>
</blockquote><p> In the StatusPicker's constructor we create a cursor over the status
table indexed by the name field. We then iterate over each record in the
status table inserting each name into the combobox. We store the
statusid for each name in the index2id <a href="qmap.html">QMap</a> using the same QMap index as
the combobox index.
<p> <pre> int StatusPicker::statusId() const
{
return index2id[ currentItem() ];
}
</pre>
<p> The statusid property READ function simply involves looking up the
combobox's index for the currently selected item in the index2id QMap
which maps combobox indexes to statusids.
<p> <pre> void StatusPicker::setStatusId( int statusid )
{
QMap<int,int>::Iterator it;
for ( it = index2id.begin(); it != index2id.end(); ++it ) {
if ( it.data() == statusid ) {
setCurrentItem( it.key() );
break;
}
}
}
</pre>
<p> The statusId() function implements the statusid property's WRITE
function. We create an iterator over a QMap and iterate over the
index2id QMap. We compare each index2id element's data (statusid) to
the id parameter's value. If we have a match we set the combobox's
current item to the index2id element's key (the combobox index), and
leave the loop.
<p> When the user edits the status field in the <a href="qdatatable.html">QDataTable</a> they will be
presented with a combobox of valid status names taken from the status
table. However the status displayed is still the raw statusid. To
display the status name when the field isn't being edited requires us
to subclass QDataTable and reimplement the paintField() function.
<p>
<pre> class CustomTable : public <a href="qdatatable.html">QDataTable</a>
{
Q_OBJECT
public:
CustomTable(
<a href="qsqlcursor.html">QSqlCursor</a> *cursor, bool autoPopulate = FALSE,
<a href="qwidget.html">QWidget</a> * parent = 0, const char * name = 0 ) :
<a href="qdatatable.html">QDataTable</a>( cursor, autoPopulate, parent, name ) {}
void paintField(
<a href="qpainter.html">QPainter</a> * p, const <a href="qsqlfield.html">QSqlField</a>* field, const <a href="qrect.html">QRect</a> & cr, bool );
};
</pre><blockquote><p align="center"><em> From <a href="sql-overview-table4-main-h.html">sql/overview/table4/main.h</a>
</em></p>
</blockquote><p> We simply call the original <a href="qdatatable.html">QDataTable</a> constructor without changing
anything. We also declare the paintField function.
<p>
<pre> <a name="x2245"></a>void CustomTable::<a href="qdatatable.html#paintField">paintField</a>( <a href="qpainter.html">QPainter</a> * p, const <a href="qsqlfield.html">QSqlField</a>* field,
const <a href="qrect.html">QRect</a> & cr, bool b)
{
if ( !field )
return;
<a name="x2249"></a> if ( field-><a href="qsqlfield.html#name">name</a>() == "statusid" ) {
<a href="qsqlquery.html">QSqlQuery</a> query( "SELECT name FROM status WHERE id=" +
<a name="x2250"></a> field-><a href="qsqlfield.html#value">value</a>().toString() );
<a href="qstring.html">QString</a> text;
if ( query.<a href="qsqlquery.html#next">next</a>() ) {
<a name="x2252"></a> text = query.<a href="qsqlquery.html#value">value</a>( 0 ).toString();
}
p-><a href="qpainter.html#drawText">drawText</a>( 2,2, cr.<a href="qrect.html#width">width</a>()-4, cr.<a href="qrect.html#height">height</a>()-4, fieldAlignment( field ), text );
}
else {
QDataTable::<a href="qdatatable.html#paintField">paintField</a>( p, field, cr, b) ;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-table4-main-cpp.html">sql/overview/table4/main.cpp</a>
</em></p>
</blockquote><p> The paintField code is based on <a href="qdatatable.html">QDataTable</a>'s source code. We need to
make three changes. Firstly add an if clause <tt>field->name() == "statusid"</tt> and look up the textual value for the id with a
straighforward <a href="qsqlquery.html">QSqlQuery</a>. Secondly call the superclass to handle other
fields. The last change is in our main function where we change
staffTable from being a QDataTable to being a CustomTable.
<p> <a name="Subclassing_QSqlCursor"></a>
<h2> Subclassing <a href="qsqlcursor.html">QSqlCursor</a>
</h2>
<a name="9"></a><p>
<pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qsqldatabase-h.html">qsqldatabase.h</a>>
#include <<a href="qsqlcursor-h.html">qsqlcursor.h</a>>
#include <<a href="qdatatable-h.html">qdatatable.h</a>>
#include "../connection.h"
int main( int argc, char *argv[] )
{
<a href="qapplication.html">QApplication</a> app( argc, argv );
if ( createConnections() ) {
<a href="qsqlcursor.html">QSqlCursor</a> invoiceItemCursor( "invoiceitem" );
<a href="qdatatable.html">QDataTable</a> *invoiceItemTable = new <a href="qdatatable.html">QDataTable</a>( &invoiceItemCursor );
app.<a href="qapplication.html#setMainWidget">setMainWidget</a>( invoiceItemTable );
<a name="x2255"></a> invoiceItemTable-><a href="qdatatable.html#addColumn">addColumn</a>( "pricesid", "PriceID" );
invoiceItemTable-><a href="qdatatable.html#addColumn">addColumn</a>( "quantity", "Quantity" );
invoiceItemTable-><a href="qdatatable.html#addColumn">addColumn</a>( "paiddate", "Paid" );
<a name="x2256"></a> invoiceItemTable-><a href="qdatatable.html#refresh">refresh</a>();
invoiceItemTable-><a href="qwidget.html#show">show</a>();
return app.<a href="qapplication.html#exec">exec</a>();
}
return 1;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-subclass1-main-cpp.html">sql/overview/subclass1/main.cpp</a>
</em></p>
</blockquote><p> This example is very similar to the table1 example presented earlier. We
create a cursor, add the fields and their display labels to a <a href="qdatatable.html">QDataTable</a>,
call refresh() to load the data and call show() to show the widget.
<p> Unfortunately this example is unsatisfactory. It is tedious to set the
table name and any custom characteristics for the fields every time we
need a cursor over this table. And it would be far better if we
displayed the name of the product rather than its pricesid. Since we
know the price of the product and the quantity we could also show the
product cost and the cost of each invoiceitem. Finally it would be
useful (or even essential for primary keys) if we could default some of
the values when the user adds a new record.
<p>
<pre> class InvoiceItemCursor : public <a href="qsqlcursor.html">QSqlCursor</a>
{
public:
InvoiceItemCursor();
};
</pre><blockquote><p align="center"><em> From <a href="sql-overview-subclass2-main-h.html">sql/overview/subclass2/main.h</a>
</em></p>
</blockquote><p> We have created a separate header file and subclassed <a href="qsqlcursor.html">QSqlCursor</a>.
<p>
<pre> InvoiceItemCursor::InvoiceItemCursor() :
<a href="qsqlcursor.html">QSqlCursor</a>( "invoiceitem" )
{
// NOOP
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-subclass2-main-cpp.html">sql/overview/subclass2/main.cpp</a>
</em></p>
</blockquote><p> In our class's constructor we call the QSqlCursor constructor with the
name of the table. We don't have any other characteristics to add at
this stage.
<p> <pre> InvoiceItemCursor invoiceItemCursor;
</pre>
<p> Whenever we require a cursor over the invoiceitem table we can create
an InvoiceItemCursor instead of a generic QSqlCursor.
<p> We still need to show the product name rather than the pricesid.
<p>
<pre> protected:
<a href="qvariant.html">QVariant</a> calculateField( const <a href="qstring.html">QString</a> & name );
</pre><blockquote><p align="center"><em> From <a href="sql-overview-subclass3-main-h.html">sql/overview/subclass3/main.h</a>
</em></p>
</blockquote><p> The change in the header file is minimal: we simply add the signature
of the calculateField() function since we will be reimplementing it.
<p>
<pre> InvoiceItemCursor::InvoiceItemCursor() :
<a href="qsqlcursor.html">QSqlCursor</a>( "invoiceitem" )
{
<a href="qsqlfieldinfo.html">QSqlFieldInfo</a> productName( "productname", QVariant::String );
<a href="qsqlcursor.html#append">append</a>( productName );
<a name="x2260"></a> <a href="qsqlcursor.html#setCalculated">setCalculated</a>( productName.<a href="qsqlfieldinfo.html#name">name</a>(), TRUE );
}
<a name="x2259"></a>QVariant InvoiceItemCursor::<a href="qsqlcursor.html#calculateField">calculateField</a>( const <a href="qstring.html">QString</a> & name )
{
if ( name == "productname" ) {
<a href="qsqlquery.html">QSqlQuery</a> query( "SELECT name FROM prices WHERE id=" +
<a href="qsqlrecord.html#field">field</a>( "pricesid" )->value().toString() );
if ( query.<a href="qsqlquery.html#next">next</a>() )
<a name="x2262"></a> return query.<a href="qsqlquery.html#value">value</a>( 0 );
}
return QVariant( <a href="qstring.html#QString-null">QString::null</a> );
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-subclass3-main-cpp.html">sql/overview/subclass3/main.cpp</a>
</em></p>
</blockquote><p> We have changed the InvoiceItemCursor constructor. We now create a new
<a href="qsqlfield.html">QSqlField</a> called productname and append this to the
InvoiceItemCursor's set of fields. We call setCalculated() on
productname to identify it as a calculated field. The first argument
to setCalculated() is the field name, the second a bool which if TRUE
signifies that calculateField() must be called to get the field's
value.
<p> <pre> <a name="x2258"></a> invoiceItemTable-><a href="qdatatable.html#addColumn">addColumn</a>( "productname", "Product" );
</pre>
<p> We add our new fields with addColumn() which adds them to the form and
sets their display names.
<p> We have to define our own calculateField() function. In our example
database the pricesid in the invoiceitem table is a foreign key into
the prices table. We find the name of the product by executing a query
on the prices table using the pricesid. This returns the product's
name.
<p> We are now able to extend the example to include calculated fields
which perform real calculations.
<p> The header file, <a href="sql-overview-subclass4-main-h.html">sql/overview/subclass4/main.h</a>, remains unchanged
from the previous example, but the constructor and calculateField()
function require some simple expansion. We'll look at each in turn.
<p>
<pre> InvoiceItemCursor::InvoiceItemCursor() :
<a href="qsqlcursor.html">QSqlCursor</a>( "invoiceitem" )
{
<a href="qsqlfieldinfo.html">QSqlFieldInfo</a> productName( "productname", QVariant::String );
<a href="qsqlcursor.html#append">append</a>( productName );
<a name="x2264"></a> <a href="qsqlcursor.html#setCalculated">setCalculated</a>( productName.<a href="qsqlfieldinfo.html#name">name</a>(), TRUE );
<a href="qsqlfieldinfo.html">QSqlFieldInfo</a> productPrice( "price", QVariant::Double );
<a href="qsqlcursor.html#append">append</a>( productPrice );
<a href="qsqlcursor.html#setCalculated">setCalculated</a>( productPrice.<a href="qsqlfieldinfo.html#name">name</a>(), TRUE );
<a href="qsqlfieldinfo.html">QSqlFieldInfo</a> productCost( "cost", QVariant::Double );
<a href="qsqlcursor.html#append">append</a>( productCost );
<a href="qsqlcursor.html#setCalculated">setCalculated</a>( productCost.<a href="qsqlfieldinfo.html#name">name</a>(), TRUE );
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-subclass4-main-cpp.html">sql/overview/subclass4/main.cpp</a>
</em></p>
</blockquote><p> We create two extra fields, price and cost, and append them to the
cursor's set of fields. Both are registered as calculated fields with
calls to setCalculated().
<p> <pre> <a name="x2263"></a>QVariant InvoiceItemCursor::<a href="qsqlcursor.html#calculateField">calculateField</a>( const <a href="qstring.html">QString</a> & name )
{
if ( name == "productname" ) {
<a href="qsqlquery.html">QSqlQuery</a> query( "SELECT name FROM prices WHERE id=" +
<a href="qsqlrecord.html#field">field</a>( "pricesid" )->value().toString() );
<a name="x2265"></a> if ( query.<a href="qsqlquery.html#next">next</a>() )
<a name="x2266"></a> return query.<a href="qsqlquery.html#value">value</a>( 0 );
}
else if ( name == "price" ) {
<a href="qsqlquery.html">QSqlQuery</a> query( "SELECT price FROM prices WHERE id=" +
<a href="qsqlrecord.html#field">field</a>( "pricesid" )->value().toString() );
if ( query.<a href="qsqlquery.html#next">next</a>() )
return query.<a href="qsqlquery.html#value">value</a>( 0 );
}
else if ( name == "cost" ) {
<a href="qsqlquery.html">QSqlQuery</a> query( "SELECT price FROM prices WHERE id=" +
<a href="qsqlrecord.html#field">field</a>( "pricesid" )->value().toString() );
if ( query.<a href="qsqlquery.html#next">next</a>() )
return QVariant( query.<a href="qsqlquery.html#value">value</a>( 0 ).toDouble() *
<a href="qsqlquery.html#value">value</a>( "quantity").toDouble() );
}
return QVariant( QString::null );
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-subclass4-main-cpp.html">sql/overview/subclass4/main.cpp</a>
</em></p>
</blockquote><p> The calculateField() function has expanded slightly because now we
must calculate the value of three different fields. The productname
and price fields are produced by looking up the corresponding values
in the prices table keyed by pricesid. The cost field is calculated
simply by multiplying the price by the quantity. Note that we cast the
cost to a <a href="qvariant.html">QVariant</a> since that is the type that calculateField() must
return.
<p> We've written three separate queries rather than one to make the
example more like a real application where it is more likely that each
calculated field would be a lookup against a different table or view.
<p> The last feature that we need to add is defaulting values when the
user attempts to insert a new record.
<p>
<pre> <a href="qsqlrecord.html">QSqlRecord</a> *primeInsert();
</pre><blockquote><p align="center"><em> From <a href="sql-overview-subclass5-main-h.html">sql/overview/subclass5/main.h</a>
</em></p>
</blockquote><p> We declare our own primeInsert() function since we will need to
reimplement this.
<p> The constructor and the calculateField() function remain unchanged.
<p>
<pre> <a name="x2267"></a>QSqlRecord *InvoiceItemCursor::<a href="qsqlcursor.html#primeInsert">primeInsert</a>()
{
<a href="qsqlrecord.html">QSqlRecord</a> *buffer = <a href="qsqlcursor.html#editBuffer">editBuffer</a>();
<a href="qsqlquery.html">QSqlQuery</a> query( "SELECT NEXTVAL( 'invoiceitem_seq' )" );
<a name="x2268"></a> if ( query.<a href="qsqlquery.html#next">next</a>() )
<a name="x2270"></a><a name="x2269"></a> buffer-><a href="qsqlrecord.html#setValue">setValue</a>( "id", query.<a href="qsqlquery.html#value">value</a>( 0 ) );
buffer-><a href="qsqlrecord.html#setValue">setValue</a>( "paiddate", QDate::currentDate() );
buffer-><a href="qsqlrecord.html#setValue">setValue</a>( "quantity", 1 );
return buffer;
}
</pre><blockquote><p align="center"><em> From <a href="sql-overview-subclass5-main-cpp.html">sql/overview/subclass5/main.cpp</a>
</em></p>
</blockquote><p> We get a pointer to the internal edit buffer that the cursor uses for
inserts and updates. The id field is a unique integer that we generate
using the invoiceitem_seq. We default the value of the paiddate field
to today's date and default the quantity to 1. Finally we return a
pointer to the buffer. The rest of the code is unchanged from the
previous version.
<p> <a name="Example_Tables"></a>
<h2> The Example Tables
</h2>
<a name="10"></a><p> The example tables used can be recreated with the following standard
SQL. You may need to modify the SQL to match that used by your
particular database.
<p> <pre>
create table people (id integer primary key, name char(40))
create table staff (id integer primary key, forename char(40),
surname char(40), salary float, statusid integer)
create table status (id integer primary key, name char(30))
create table creditors (id integer primary key, forename char(40),
surname char(40), city char(30))
create table prices (id integer primary key, name char(40), price float)
create table invoiceitem (id integer primary key,
pricesid integer, quantity integer,
paiddate date)
</pre>
<p> A sequence was used in the calculateField() example above. Note that
sequences are not supported in all databases.
<p> <pre>
create sequence invoiceitem_seq
</pre>
<p>
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