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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 - Drivers</h1>
<p> <ul>
<li> <a href="#Introduction">Introduction</a>
<li> <a href="#building">Building the drivers using configure</a>
<li> <a href="#buildingmanually">Building the plugins manually</a>
<ul>
<li> <a href="#QDB2">QDB2</a> - IBM DB2 Driver (v7.1 and higher)
<li> <a href="#QIBASE">QIBASE</a> - Borland Interbase Driver
<li> <a href="#QMYSQL3">QMYSQL3</a> - MySQL Driver
<li> <a href="#QOCI8">QOCI8</a> - Oracle Call Interface Driver, version 8 and 9
<li> <a href="#QODBC3">QODBC3</a> - Open Database Connectivity Driver
<li> <a href="#QPSQL7">QPSQL7</a> - PostgreSQL v6.x and v7.x Driver
<li> <a href="#QSQLITE">QSQLITE</a> - SQLite Driver
<li> <a href="#QTDS7">QTDS7</a> - Sybase Adaptive Server
</ul>
<li> <a href="#troubleshooting">Troubleshooting</a>
<li> <a href="#development">How to write your own database driver</a>
</ul>
<p> <a name="Introduction"></a>
<h2> Introduction
</h2>
<a name="1"></a><p> The <a href="sql.html">SQL Module</a> uses driver <a href="plugins-howto.html">plugins</a> in order to communicate with
different database APIs. Since the SQL Module API is
database-independent, all database-specific code is contained within
these drivers. Several drivers are supplied with Qt and other drivers
can be added. The driver source code is supplied and can be used as a
model for <a href="#development">writing your own drivers</a>.
<p> <em>Note:</em> To build a driver plugin you need to have the appropriate
client library for your Database Management System (DBMS). This provides
access to the API exposed by the DBMS, and is typically shipped with it.
Most installation programs also allow you to install "development
libraries", and these are what you need. These libraries are responsible
for the low-level communication with the DBMS.
<p> The drivers shipped with Qt are:
<ul>
<li> <a href="#QDB2">QDB2</a> - IBM DB2 Driver (v7.1 and higher)
<li> <a href="#QIBASE">QIBASE</a> - Borland Interbase Driver
<li> <a href="#QMYSQL3">QMYSQL3</a> - MySQL Driver
<li> <a href="#QOCI8">QOCI8</a> - Oracle Call Interface Driver, version 8, 9 and 10
<li> <a href="#QODBC3">QODBC3</a> - Open Database Connectivity Driver
<li> <a href="#QPSQL7">QPSQL7</a> - PostgreSQL v6.x and v7.x Driver
<li> <a href="#QSQLITE">QSQLITE</a> - SQLite Driver
<li> <a href="#QTDS7">QTDS7</a> - Sybase Adaptive Server
</ul>
<p> Note that not all of the plugins are shipped with the Qt Open Source Edition
due to license incompatibilities with the GPL.
<p> <a name="building"></a>
<h2> Building the drivers using configure
</h2>
<a name="2"></a><p> The Qt configure script automatically detects the available client
libraries on your machine. Run "configure -help" to see what drivers
can be built. You should get an output similar to this:
<p> <pre>
Possible values for <driver>: [ mysql oci odbc psql tds ]
Auto-Detected on this system: [ mysql psql ]
</pre>
<p> Note that on Windows, the configure script doesn't do any
auto-detection.
<p> The configure script cannot detect the neccessary libraries and include
files if they are not in the standard paths, so it may be necessary to
specify these paths using the "-I" and "-L" switches. For example, if
your MySQL include files are installed in <tt>/usr/local/mysql</tt> (or in
<tt>C:\mysql\include</tt>
configure: <tt>-I/usr/local/mysql</tt> (or <tt>-I C:\mysql\include</tt>
Windows).
<p> On Windows the -I parameter doesn't accept spaces in
filenames, so use the 8.3 name instead, i.e. use <tt>C:\progra~1\mysql</tt>
instead of <tt>C:\program files\mysql</tt>.
<p> Use the <tt>-qt-sql-<driver></tt> parameter to build the database driver
statically into your Qt library or <tt>-plugin-sql-<driver></tt> to build
the driver as a plugin. Look at the sections that follow for
additional information about required libraries.
<p> <a name="buildingmanually"></a>
<h2> Building the plugins manually
</h2>
<a name="3"></a><p> <a name="QMYSQL3"></a>
<h3> QMYSQL3 - MySQL 3.x and MySQL 4.x
</h3>
<a name="3-1"></a><p> <!-- index QMYSQL3 --><a name="QMYSQL3"></a>
<p> <h4> General information
</h4>
<a name="3-1-1"></a><p> MySQL 3.x doesn't support SQL transactions by default. There are some
backends which offer this functionality. Recent versions of the MySQL
client libraries (>3.23.34) allow you to use transactions on those
modified servers.
<p> If you have a recent client library and connect to a
transaction-enabled MySQL server, a call to the
<a href="qsqldriver.html#hasFeature">QSqlDriver::hasFeature</a>( QSqlDriver::Transactions ) function returns
TRUE and SQL transactions can be used.
<p> If the plugin is compiled against MySQL 4.x client libraries,
transactions are enabled by default.
<p> You can find information about MySQL on <a href="http://www.mysql.com">http://www.mysql.com</a>
<p> <h4> How to build the plugin on Unix/Linux
</h4>
<a name="3-1-2"></a><p> You need the MySQL header files and as well as the shared library
<tt>libmysqlclient.so</tt>. Depending on your Linux distribution you need to
install a package which is usually called "mysql-devel".
<p> Tell <a href="qmake-manual.html">qmake</a> where to find the MySQL
header files and shared libraries (here it is assumed that MySQL is
installed in <tt>/usr/local</tt>) and run <tt>make</tt>:
<p> <pre>
cd $QTDIR/plugins/src/sqldrivers/mysql
qmake -o Makefile "INCLUDEPATH+=/usr/local/include" "LIBS+=-L/usr/local/lib -lmysqlclient" mysql.pro
make
</pre>
<p> <h4> How to build the plugin on Windows
</h4>
<a name="3-1-3"></a><p> You need to get the MySQL installation files. Run SETUP.EXE and
choose "Custom Install". Install the "Libs & Include Files" Module.
Build the plugin as follows (here it is assumed that MySQL is
installed in <tt>C:\MYSQL</tt>):
<p> <pre>
cd %QTDIR%\plugins\src\sqldrivers\mysql
qmake -o Makefile "INCLUDEPATH+=C:\MYSQL\INCLUDE" "LIBS+=C:\MYSQL\LIB\OPT\LIBMYSQL.LIB" mysql.pro
nmake
</pre>
<p> If you are not using a Microsoft compiler, replace <tt>nmake</tt> with <tt>make</tt> in the statement above.
<p> <a name="QOCI8"></a>
<h3> QOCI8 - Oracle Call Interface (OCI)
</h3>
<a name="3-2"></a><p> <!-- index QOCI8 --><a name="QOCI8"></a>
<p> <h4> General information
</h4>
<a name="3-2-1"></a><p> The Qt OCI plugin supports both Oracle 8 and Oracle 9. After
connecting to the Oracle server, the plugin will auto-detect the
database version and enable features accordingly.
<p> <h4> Unicode support
</h4>
<a name="3-2-2"></a><p> If the Oracle server supports Unicode, the OCI plugin will use UTF-8
encoding to communicate with the server.
<p> <h4> BLOB/LOB support
</h4>
<a name="3-2-3"></a><p> Binary Large Objects (BLOBs) can be read and written, but be aware
that this process may require a lot of memory.
<p> Note that Oracle 9 doesn't support scrollable result sets with LOB
columns, you have to use a forward only query to select LOB fields
(see <a href="qsqlquery.html#setForwardOnly">QSqlQuery::setForwardOnly</a>()).
<p> Inserting BLOBs should be done using either a prepared query where the
BLOBs are bound to placeholders, or <a href="qsqlcursor.html">QSqlCursor</a> which uses a prepared
query to do this internally (see $QTDIR/examples/sql/blob).
<p> <h4> Know problems
</h4>
<a name="3-2-4"></a><p> When a query is in forward only mode a call to <a href="qsqlquery.html#last">QSqlQuery::last</a>() will
position the query on the last record and return TRUE, but subsequent
calls to <a href="qsqlquery.html#value">QSqlQuery::value</a>() will only return NULLs.
<p> <h4> How to build the plugin on Unix/Linux
</h4>
<a name="3-2-5"></a><p> All files required to build driver should ship with the standard Oracle
Client install.
<p> Oracle library files required to build driver:
<p> <ul>
<li> <tt>libclntsh.so</tt> (all versions)
<li> <tt>libwtc8.so</tt> (only Oracle 8) or <tt>libwtc9.so</tt> (only Oracle 9)
</ul>
<p> Tell <tt>qmake</tt> where to find the Oracle header files and shared
libraries (it is assumed that the variable <tt>$ORACLE_HOME</tt> points to
the directory where Oracle is installed) and run make:
<p> If you are using Oracle 8:
<pre>
cd $QTDIR/plugins/src/sqldrivers/oci
qmake -o Makefile "INCLUDEPATH+=$ORACLE_HOME/rdbms/public $ORACLE_HOME/rdbms/demo" "LIBS+=-L$ORACLE_HOME/lib -lclntsh -lwtc8" oci.pro
make
</pre>
<p> For Oracle version 9:
<pre>
cd $QTDIR/plugins/src/sqldrivers/oci
qmake -o Makefile "INCLUDEPATH+=$ORACLE_HOME/rdbms/public $ORACLE_HOME/rdbms/demo" "LIBS+=-L$ORACLE_HOME/lib -lclntsh -lwtc9" oci.pro
make
</pre>
<p> For Oracle version 10:
<pre>
cd $QTDIR/plugins/src/sqldrivers/oci
qmake -o Makefile "INCLUDEPATH+=$ORACLE_HOME/rdbms/public $ORACLE_HOME/rdbms/demo" "LIBS+=-L$ORACLE_HOME/lib -lclntsh" oci.pro
make
</pre>
<p> Note that some versions of the OCI client libraries contain a bug
that makes programs linked to these libraries segfault on exit. This
only happens if the QOCI8 driver is compiled as a plugin. To work
around this problem, either compile the driver into the Qt libray
itself, or configure Qt with the option '-DQT_NO_LIBRARY_UNLOAD'.
For Oracle 9, it is possible to link to the static OCI library by
using "LIBS+=$ORACLE_HOME/lib/libclntst9.a".
<p> <h4> How to build the plugin on Windows
</h4>
<a name="3-2-6"></a><p> Choosing the option "Programmer" in the Oracle Client Installer from
the Oracle Client Installation CD is sufficient to build the plugin.
<p> Build the plugin as follows (here it is assumed that Oracle Client is
installed in <tt>C:\oracle</tt>):
<p> <pre>
set INCLUDE=%INCLUDE%;c:\oracle\oci\include
set LIB=%LIB%;c:\oracle\oci\lib\msvc
cd %QTDIR%\plugins\src\sqldrivers\oci
qmake -o Makefile oci.pro
nmake
</pre>
<p> When you run your application you will also need to add the <tt>oci.dll</tt>
path to your <tt>PATH</tt> environment variable:
<p> <pre>
set PATH=%PATH%;c:\oracle\bin
</pre>
<p> If you are not using a Microsoft compiler, replace <tt>nmake</tt> with <tt>make</tt> in the statement above.
<p> <a name="QODBC3"></a>
<h3> QODBC3 - Open Database Connectivity (ODBC)
</h3>
<a name="3-3"></a><p> <!-- index QODBC3 --><a name="QODBC3"></a>
<p> <h4> General information
</h4>
<a name="3-3-1"></a><p> ODBC is a general interface that allows you to connect to multiple
DBMS using a common interface. The QODBC3 driver allows you to connect
to an ODBC driver manager and access the available data sources. Note
that you also need to install and configure ODBC drivers for the ODBC
driver manager that is installed on your system. The QODBC3 plugin
then allows you to use these data sources in your Qt project.
<p> On Windows systems after 95 an ODBC driver manager should be installed
by default, for Unix systems there are some implementations which must
be installed first. Note that every client that uses your application
is required to have an ODBC driver manager installed, otherwise the
QODBC3 plugin will not work.
<p> Be aware that when connecting to an ODBC datasource you must pass in
the name of the ODBC datasource to the <a href="qsqldatabase.html#setDatabaseName">QSqlDatabase::setDatabaseName</a>()
function: not the actual database name.
<p> The QODBC3 Plugin needs an ODBC compliant driver manager version 2.0 or
later to work. Some ODBC drivers claim to be version 2.0 compliant,
but do not offer all the necessary functionality. The QODBC3 plugin
therefore checks whether the data source can be used after a
connection has been established and refuses to work if the check
fails. If you don't like this behaviour, you can remove the <tt>#define ODBC_CHECK_DRIVER</tt> line from the file <tt>qsql_odbc.cpp</tt>. Do this at
your own risk!
<p> If you experience very slow access of the ODBC datasource, make sure
that ODBC call tracing is turned off in the ODBC datasource manager.
<p> <h4> Unicode support
</h4>
<a name="3-3-2"></a><p> The QODBC3 Plugin will use the Unicode API if UNICODE is defined. On
Windows NT based systems, this is the default. Note that the ODBC
driver and the DBMS have to support Unicode as well.
<p> For the Oracle 9 ODBC driver (Windows), it is neccessary to check
"SQL_WCHAR support" in the ODBC driver manager otherwise Oracle
will convert all Unicode strings to local 8 bit.
<p> <h4> How to build the plugin on Unix/Linux
</h4>
<a name="3-3-3"></a><p> It is recommended that you use unixODBC. You can find the latest
version and ODBC drivers at <a href="http://www.unixodbc.org">http://www.unixodbc.org</a>.
You need the unixODBC header files and shared libraries.
<p> Tell <tt>qmake</tt> where to find the unixODBC header files and shared
libraries (here it is assumed that unixODBC is installed in
<tt>/usr/local/unixODBC</tt>) and run <tt>make</tt>:
<p> <pre>
cd $QTDIR/plugins/src/sqldrivers/odbc
qmake "INCLUDEPATH+=/usr/local/unixODBC/include" "LIBS+=-L/usr/local/unixODBC/lib -lodbc"
make
</pre>
<p> <h4> How to build the plugin on Windows
</h4>
<a name="3-3-4"></a><p> The ODBC header and include files should already be installed in the
right directories. You just have to build the plugin as follows:
<p> <pre>
cd %QTDIR%\plugins\src\sqldrivers\odbc
qmake -o Makefile odbc.pro
nmake
</pre>
<p> If you are not using a Microsoft compiler, replace <tt>nmake</tt> with <tt>make</tt> in the statement above.
<p> <a name="QPSQL7"></a>
<h3> QPSQL7 - PostgreSQL version 6 and 7
</h3>
<a name="3-4"></a><p> <!-- index QPSQL7 --><a name="QPSQL7"></a>
<p> <h4> General information
</h4>
<a name="3-4-1"></a><p> The QPSQL7 driver supports both version 6 and 7 of PostgreSQL. We
recommend compiling the plugin with a recent version of the PostgreSQL
client library (libpq) because it is more stable and still backwards
compatible.
<p> If you want to link the plugin against the libpq shipped with version
6 we recommend a recent version like PostgreSQL 6.5.3, otherwise a
connection to a version 7 server may not work.
<p> The driver auto-detects the server version of PostgreSQL after a
connection was successful. If the server is too old or the version
information cannot be determined a warning is issued.
<p> For more information about PostgreSQL visit <a href="http://www.postgresql.org">http://www.postgresql.org</a>.
<p> <h4> Unicode support
</h4>
<a name="3-4-2"></a><p> The QPSQL7 driver automatically detects whether the PostgreSQL
database you are connecting to supports Unicode or not. Unicode is
automatically used if the server supports it. Note that the driver
only supports the UTF-8 encoding. If your database uses any other
encoding, the server must be compiled with Unicode conversion
support.
<p> Unicode support was introduced in PostgreSQL version 7.1 and it will
only work if both the server and the client library have been compiled
with multibyte support. More information about how to set up a
multibyte enabled PostgreSQL server can be found in the PostgreSQL
Administrator Guide, Chapter 5.
<p> <h4> BLOB support
</h4>
<a name="3-4-3"></a><p> Binary Large Objects are supported through the <tt>BYTEA</tt> field type in
PostgreSQL versions >= 7.1. Fields of type <tt>OID</tt> can be read, but not
written. Use the PostgreSQL command <tt>lo_import</tt> to insert binary data
into <tt>OID</tt> fields.
<p> <h4> How to build the plugin on Unix/Linux
</h4>
<a name="3-4-4"></a><p> Just installing the pq client library and the corresponding header
files is not sufficient. You have to get the PostgreSQL source
distribution and run the configure script. If you've already installed
a binary distribution you don't need to build it. The source
distribution is needed because the QPSQL7 plugin relies on a couple of
header files that are usually not a part of the binary distribution.
<p> To make <tt>qmake</tt> find the PostgreSQL header files and shared
libraries, run <tt>qmake</tt> the following way (assuming that the
PostgreSQL sources can be found in <tt>/usr/src/psql</tt>):
<p> <pre>
cd $QTDIR/plugins/src/sqldrivers/psql
qmake -o Makefile "INCLUDEPATH+=/usr/src/psql/src/include /usr/src/psql/src/interfaces/libpq" "LIBS+=-L/usr/lib -lpq" psql.pro
make
</pre>
<p> <h4> How to build the plugin on Windows
</h4>
<a name="3-4-5"></a><p> Unpack and build the PostgreSQL source distribution as described in
the PostgreSQL documentation. Assuming the PostgreSQL sources resides
in <tt>C:\psql</tt>, build the plugin as follows:
<p> <pre>
cd %QTDIR%\plugins\src\sqldrivers\psql
qmake -o Makefile "INCLUDEPATH+=C:\psql\src\include C:\psql\src\interfaces\libpq" psql.pro
nmake
</pre>
<p> Remember to add the path to the <tt>libpq.dll</tt> library to your PATH
environment variable so that Windows can find it. In this case that
would be <tt>C:\psql\src\interfaces\libpq\Release</tt>. If you are not using a
Microsoft compiler, replace <tt>nmake</tt> with <tt>make</tt> in the statement
above.
<p> <a name="QTDS7"></a>
<h3> QTDS7 - Sybase Adaptive Server
</h3>
<a name="3-5"></a><p> <!-- index QTDS7 --><a name="QTDS7"></a>
<p> <h4> How to build the plugin on Unix/Linux
</h4>
<a name="3-5-1"></a><p> Under Unix, two libraries are available which support the TDS protocol:
<p> - FreeTDS, a free implementation of the TDS protocol
(<a href="http://www.freetds.org">http://www.freetds.org</a>). Note that FreeTDS is not yet stable,
so some functionality may not work as expected.
<p> - Sybase Open Client, available from <a href="http://www.sybase.com">http://www.sybase.com</a>.
Note for Linux users: Get the Open Client RPM from
<a href="http://linux.sybase.com">http://linux.sybase.com</a>.
<p> Regardless of which library you use, the shared object file
<tt>libsybdb.so</tt> is needed. Set the SYBASE environment variable to
point to the directory where you installed the client library and
execute <tt>qmake</tt>:
<p> <pre>
cd $QTDIR/plugins/src/sqldrivers/tds
qmake -o Makefile "INCLUDEPATH=$SYBASE/include" "LIBS=-L$SYBASE/lib -lsybdb"
make
</pre>
<p> <h4> How to build the plugin on Windows
</h4>
<a name="3-5-2"></a><p> You can either use the DB-Library supplied by Microsoft or the Sybase
Open Client (<a href="http://www.sybase.com">http://www.sybase.com</a>). You must include <tt>NTWDBLIB.LIB</tt> to build the plugin:
<p> <pre>
cd %QTDIR%\plugins\src\sqldrivers\tds
qmake -o Makefile "LIBS+=NTWDBLIB.LIB" tds.pro
nmake
</pre>
<p> By default the Microsoft library is used on Windows, if you want to force
the use of the Sybase Open Client, you must define
<tt>Q_USE_SYBASE</tt> in <tt>%QTDIR%\src\sql\drivers\tds\qsql_tds.cpp</tt>.
<p> <a name="QDB2"></a>
<h3> QDB2 - IBM DB2 Driver (v7.1 or higher)
</h3>
<a name="3-6"></a><p> <!-- index QDB2 --><a name="QDB2"></a>
<p> <h4> General information
</h4>
<a name="3-6-1"></a><p> The Qt DB2 plugin makes it possible to access IBM DB2 databases. It
has been tested with IBM DB2 v7.1 and 7.2. You have to install the IBM
DB2 development client library, which contains the header and library
files necessary for compiling the QDB2 plugin.
<p> The QDB2 driver supports prepared queries, reading/writing of Unicode
strings and reading/writing of BLOBs.
<p> We suggest using a forward-only query when calling stored procedures
in DB2 (see <a href="qsqlquery.html#setForwardOnly">QSqlQuery::setForwardOnly</a>()).
<p> <h4> How to build the plugin on Unix/Linux
</h4>
<a name="3-6-2"></a><p> <pre>
cd $QTDIR/plugins/src/sqldrivers/db2
qmake -o Makefile "INCLUDEPATH+=$DB2DIR/include" "LIBS+=-L$DB2DIR/lib -ldb2"
make
</pre>
<p> <h4> How to build the plugin on Windows
</h4>
<a name="3-6-3"></a><p> The DB2 header and include files should already be installed in the
right directories. You just have to build the plugin as follows:
<p> <pre>
cd %QTDIR%\plugins\src\sqldrivers\db2
qmake -o Makefile "INCLUDEPATH+=<DB2 home>/sqllib/include" "LIBS+=<DB2 home>/sqllib/lib/db2cli.lib"
nmake
</pre>
<p> If you are not using a Microsoft compiler, replace <tt>nmake</tt>
with <tt>make</tt> in the statement above.
<p> <a name="QSQLITE"></a>
<h3> QSQLITE - SQLite Driver
</h3>
<a name="3-7"></a><p> <!-- index QSQLITE --><a name="QSQLITE"></a>
<p> The Qt SQLite plugin makes it possible to access SQLite databases.
SQLite is an in-process database, meaning that it is not necessary
to have a database server. SQLite operates on a single file, which has
to be set as database name when opening a connection. If the file does
not exist, SQLite will try to create it. SQLite also supports in-memory
databases, simply pass ":memory:" as the database name.
<p> SQLite has some restrictions regarding multiple users and
multiple transactions. If you try to read/write on a resource from different
transactions, your application might freeze until one transaction commits
or rolls back.
<p> SQLite has no support for types, every value is treated as character data.
BLOBs are therefore not supported.
<p> You can find information about SQLite on <a href="http://www.sqlite.org">http://www.sqlite.org</a>.
<p> SQLite is shipped as third party library within Qt. It can be built by
passing the following parameters to the configure script:
<tt>-plugin-sql-sqlite</tt> (as plugin) or <tt>-qt-sql-sqlite</tt> (linked
directly into the Qt library).
<p> If you don't want to use the SQLite library shipped with Qt, you can
build it manually (replace <tt>$SQLITE</tt> by the directory where SQLite
resides):
<p> <pre>
cd $QTDIR/plugins/src/sqldrivers/sqlite
qmake -o Makefile "INCLUDEPATH+=$SQLITE/include" "LIBS+=-L$SQLITE/lib -lsqlite"
make
</pre>
<p> <a name="QIBASE"></a>
<h3> QIBASE - Borland Interbase Driver
</h3>
<a name="3-8"></a><p> <!-- index QIBASE --><a name="QIBASE"></a>
<p> <h4> General information
</h4>
<a name="3-8-1"></a><p> The Qt Interbase plugin makes it possible to access the Interbase and
Firebird databases. Interbase can either be used as a client/server or
without a server operating on local files. The database file must
exist before a connection can be established.
<p> Note that Interbase requires you to specify the full path to the
database file, no matter whether it is stored locally or on another
server.
<p> <pre>
myDatabase->setHostName("MyServer");
myDatabase->setDatabaseName("C:\\test.gdb");
</pre>
<p> You need the Interbase/Firebird development headers and libraries
to build this plugin.
<p> Due to the GPL, users of the Qt Open Source Edition are not allowed to link
this plugin to the commercial editions of Interbase. Please use Firebird
or the free edition of Interbase.
<p> <h4> How to build the plugin on Unix/Linux
</h4>
<a name="3-8-2"></a><p> The following assumes Interbase or Firebird is installed in
<tt>/opt/interbase</tt>:
<p> <pre>
cd $QTDIR/plugins/src/sqldrivers/ibase
qmake -o Makefile "INCLUDEPATH+=/opt/interbase/include" "LIBS+=-L/opt/interbase/lib" ibase.pro
make
</pre>
<p> <h4> How to build the plugin on Windows
</h4>
<a name="3-8-3"></a><p> The following assumes Interbase or Firebird is installed in
<tt>C:\interbase</tt>:
<p> <pre>
cd %QTDIR%\plugins\src\sqldrivers\ibase
qmake -o Makefile "INCLUDEPATH+=C:\interbase\include" ibase.pro
nmake
</pre>
<p> If you are not using a Microsoft compiler, replace <tt>nmake</tt>
with <tt>make</tt> in the statement above.
<p> Note that <tt>C:\interbase\bin</tt> must be in the PATH.
<p> <a name="troubleshooting"></a>
<h2> Troubleshooting
</h2>
<a name="4"></a><p> You should always use client libraries that have been compiled with
the same compiler as you are using for your project. If you cannot get
a source distibution to compile the client libraries yourself, you
must make sure that the pre-compiled library is compatible with
your compiler, otherwise you will get a lot of "undefined symbols"
errors. Some compilers have tools to convert libraries, e.g. Borland
ships the tool <tt>COFF2OMF.EXE</tt> to convert libraries that have been
generated with Microsoft Visual C++.
<p> If the compilation of a plugin succeeds but it cannot be loaded,
make sure that the following requirements are met:
<p> <ul>
<li> Ensure that you are using a shared Qt library; you cannot use the
plugins with a static build.
<li> Ensure that the environment variable <tt>QTDIR</tt> points to the right
directory. Go to the <tt>$QTDIR/plugins/sqldrivers</tt> directory and
make sure that the plugin exists in that directory.
<li> Ensure that the client libraries of the DBMS are available on the
system. On Unix, run the command <tt>ldd</tt> and pass the name of the
plugin as parameter, for example <tt>ldd libqsqlmysql.so</tt>. You will
get a warning if any of the client libraries couldn't be found.
On Windows, you can use the dependency walker of Visual Studio.
</ul>
<p> If you are experiencing problems with loading plugins, and see output
like this
<p> <pre>
QSqlDatabase warning: QMYSQL3 driver not loaded
QSqlDatabase: available drivers: QMYSQL3
</pre>
<p> the problem is probably that the plugin had the wrong build key. For
debugging purposes, remove the corresponding entry in the
$HOME/.qt/qt_plugins_(qtversion).rc file.
<p> The next time you try to load this plugin, it will give you a more detailed
error message.
<p> <a name="development"></a>
<h2> How to write your own database driver
</h2>
<a name="5"></a><p> <a href="qsqldatabase.html">QSqlDatabase</a> is responsible for loading and managing database driver
plugins. When a database is added (see <a href="qsqldatabase.html#addDatabase">QSqlDatabase::addDatabase</a>()),
the appropriate driver plugin is loaded (using <a href="qsqldriverplugin.html">QSqlDriverPlugin</a>).
QSqlDatabase relies on the driver plugin to provide interfaces for
<a href="qsqldriver.html">QSqlDriver</a> and <a href="qsqlresult.html">QSqlResult</a>.
<p> QSqlDriver is an abstract base class which defines the functionality
of a SQL database driver. This includes functions such as
<a href="qsqldriver.html#open">QSqlDriver::open</a>() and <a href="qsqldriver.html#close">QSqlDriver::close</a>(). QSqlDriver is responsible
for connecting to a database, establish the proper environment, etc.
In addition, QSqlDriver can create <a href="qsqlquery.html">QSqlQuery</a> objects appropriate for
the particular database API. QSqlDatabase forwards many of its
function calls directly to QSqlDriver which provides the concrete
implementation.
<p> QSqlResult is an abstract base class which defines the functionality
of a SQL database query. This includes statements such as <tt>SELECT</tt>,
<tt>UPDATE</tt>, and <tt>ALTER TABLE</tt>. QSqlResult contains functions such as
QSqlResult::next() and QSqlResult::value(). QSqlResult is responsible
for sending queries to the database, returning result data, etc.
QSqlQuery forwards many of its function calls directly to <a href="qsqlresult.html">QSqlResult</a>
which provides the concrete implementation.
<p> <a href="qsqldriver.html">QSqlDriver</a> and QSqlResult are closely connected. When implementing a
Qt SQL driver, both of these classes must to be subclassed and the
abstract virtual methods in each class must be implemented.
<p> To implement a Qt SQL driver as a plugin (so that it is recognized and
loaded by the Qt library at runtime), the driver must use the
<tt>Q_EXPORT_PLUGIN</tt> macro. Read the <a href="plugins-howto.html">Qt
Plugin</a> documentation for more information on this. You can
also check out how this is done in the SQL plugins that is provided
with Qt in <tt>QTDIR/plugins/src/sqldrivers</tt> and
<tt>QTDIR/src/sql/drivers</tt>.
<p> The following code can be used as a skeleton for a SQL driver:
<p> <pre>
class QNullResult : public <a href="qsqlresult.html">QSqlResult</a>
{
public:
QNullResult( const <a href="qsqldriver.html">QSqlDriver</a>* d ): <a href="qsqlresult.html">QSqlResult</a>( d ) {}
~QNullResult() {}
protected:
<a href="qvariant.html">QVariant</a> data( int ) { return QVariant(); }
bool reset ( const <a href="qstring.html">QString</a>& ) { return FALSE; }
bool fetch( int ) { return FALSE; }
bool fetchFirst() { return FALSE; }
bool fetchLast() { return FALSE; }
bool isNull( int ) { return FALSE; }
<a href="qsqlrecord.html">QSqlRecord</a> record() { return QSqlRecord(); }
int size() { return 0; }
int numRowsAffected() { return 0; }
};
class QNullDriver : public <a href="qsqldriver.html">QSqlDriver</a>
{
public:
QNullDriver(): <a href="qsqldriver.html">QSqlDriver</a>() {}
~QNullDriver() {}
bool hasFeature( DriverFeature ) const { return FALSE; }
bool open( const <a href="qstring.html">QString</a>&,
const <a href="qstring.html">QString</a>&,
const <a href="qstring.html">QString</a>&,
const <a href="qstring.html">QString</a>&,
int ) { return FALSE; }
void close() {}
<a href="qsqlquery.html">QSqlQuery</a> createQuery() const { return QSqlQuery( new QNullResult( this ) ); }
};
</pre>
<p>
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<td>Copyright © 2007
<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
<td align=right><div align=right>Qt 3.3.8</div>
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