The SQL Module uses driver plugins 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 writing your own drivers.
To build a driver plugin you need the client API that is shipped with
your Database Management System (DBMS). 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.
QTDS7 - Sybase Adaptive Server and Microsoft SQL Server Driver
Note that not all of the plugins are shipped with the Qt Free Edition
due to license incompatibilities with the GPL.
Building the drivers using configure
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:
Possible values for <driver>: [ mysql oci odbc psql tds ]
Auto-Detected on this system: [ mysql psql ]
Note that on Windows, the configure script doesn't do any
auto-detection.
Note that configure 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 /usr/local/mysql (or in
C:\mysql\include
configure: -I/usr/local/mysql (or -I C:\mysql\include
Windows).
Note that on Windows the -I parameter doesn't allow spaces in
filenames, so use the 8.3 name instead, i.e. use C:\progra~1\mysql
instead of C:\program files\mysql.
Use the -qt-sql-<driver> parameter to build the database driver
statically into your Qt library or -plugin-sql-<driver> to build
the driver as a plugin. Look at the sections that follow for
additional information about required libraries.
Building the plugins manually
QMYSQL3 - MySQL 3.x
General information
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.
If you have a recent client library and connect to a
transaction-enabled MySQL server, a call to the
QSqlDriver::hasFeature( QSqlDriver::Transactions ) function returns
TRUE and SQL transactions can be used.
You need the MySQL header files and as well as the shared library
libmysqlclient.so. Depending on your Linux distribution you need to
install a package which is usually called "mysql-devel".
Tell qmake where to find the MySQL
header files and shared libraries (here it is assumed that MySQL is
installed in /usr/local) and run make:
cd $QTDIR/plugins/src/sqldrivers/mysql
qmake -o Makefile "INCLUDEPATH+=/usr/local/include" "LIBS+=-L/usr/local/lib -lmysqlclient" mysql.pro
make
How to build the plugin on Windows
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 C:\MYSQL):
cd %QTDIR%\plugins\src\sqldrivers\mysql
qmake -o Makefile "INCLUDEPATH+=C:\MYSQL\INCLUDE" "LIBS+=C:\MYSQL\LIB\OPT\LIBMYSQL.LIB" mysql.pro
nmake
If you are not using a Microsoft compiler, replace nmake with make in the statement above.
QOCI8 - Oracle Call Interface (OCI)
General information
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.
Unicode support
If the Oracle server supports Unicode, the OCI plugin will use UTF-8
encoding to communicate with the server. When accessing an Oracle 8
database, only retrieval of Unicode strings are supported. For Oracle
9 both retrieval and insertion of Unicode strings are supported.
BLOB/LOB support
Binary Large Objects (BLOBs) can be retrieved, but be aware that this
process may require a lot of memory. We recommend using separate
queries and retrieving only one BLOB at a time.
Inserting BLOB fields is limited to Oracle's maximum SQL string size.
How to build the plugin on Unix/Linux
All files required to build driver should ship with the standard Oracle
Client install.
Oracle library files required to build driver:
libclntsh.so
libclntsh.so.8.0 (Oracle 8) or libclntsh.so.9.0 (Oracle 9)
libwtc8.so or libwtc9.so
Tell qmake where to find the Oracle header files and shared
libraries (it is assumed that the variable $ORACLE_HOME points to
the directory where Oracle is installed) and run make:
If you are using Oracle 8:
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
For Oracle version 9:
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
How to build the plugin on Windows
Choosing the option "Programmer" in the Oracle Client Installer from
the Oracle Client Installation CD is sufficient to build the plugin.
Build the plugin as follows (here it is assumed that Oracle Client is
installed in C:\oracle):
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
When you run your application you will also need to add the oci.dll
path to your PATH environment variable:
set PATH=%PATH%;c:\oracle\bin
If you are not using a Microsoft compiler, replace nmake with make in the statement above.
QODBC3 - Open Database Connectivity (ODBC)
General information
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.
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.
Be aware that when connecting to an ODBC datasource you must pass in
the name of the ODBC datasource to the QSqlDatabase::setDatabaseName()
function: not the actual database name.
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 #define ODBC_CHECK_DRIVER line from the file qsql_odbc.cpp. Do this at
your own risk!
If you experience very slow access of the ODBC datasource, make sure
that ODBC call tracing is turned off in the ODBC datasource manager.
How to build the plugin on Unix/Linux
It is recommended that you use unixODBC. You can find the latest
version and ODBC drivers at http://www.unixodbc.org.
You need the unixODBC header files and shared libraries.
Tell qmake where to find the unixODBC header files and shared
libraries (here it is assumed that unixODBC is installed in
/usr/local/unixODBC) and run make:
cd $QTDIR/plugins/src/sqldrivers/odbc
qmake "INCLUDEPATH+=/usr/local/unixODBC/include" "LIBS+=-L/usr/local/unixODBC/lib -lodbc"
make
How to build the plugin on Windows
The ODBC header and include files should already be installed in the
right directories. You just have to build the plugin as follows:
cd %QTDIR%\plugins\src\sqldrivers\odbc
qmake -o Makefile odbc.pro
nmake
If you are not using a Microsoft compiler, replace nmake with make in the statement above.
QPSQL7 - PostgreSQL version 6 and 7
General information
The QPSQL7 driver supports both version 6 and 7 of PostgreSQL. We
recommend compiling the plugin with a recent version of the PostgreSQL
Client API (libpq) because it is more stable and still downward
compatible.
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.
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.
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.
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.
BLOB support
Binary Large Objects can be fetched but not inserted. Use the
PostgreSQL command lo_import to insert binary data into the
database.
How to build the plugin on Unix/Linux
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 (there is no need to
build it if you have already installed a binary distribution).
Tell qmake where to find the PostgreSQL header files and shared
libraries (here it is assumed that you extracted the PostgreSQL source
code in /usr/src/psql and the shared library is installed in
/usr/lib) and run make:
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
How to build the plugin on Windows
Unpack and build the PostgreSQL source distribution as described in
the PostgreSQL documentation. Build the plugin as follows (here it is
assumed that PostgreSQL is installed in C:\psql):
cd %QTDIR%\plugins\src\sqldrivers\psql
qmake -o Makefile "INCLUDEPATH+=C:\psql\src\include C:\psql\src\interfaces\libpq" psql.pro
nmake
Remember to add the path to the libpq.dll library to your PATH
environment variable so that Windows can find it. In this case that
would be C:\psql\src\interfaces\libpq\Release. If you are not using a
Microsoft compiler, replace nmake with make in the statement
above.
QTDS7 - Sybase Adaptive Server and Microsoft SQL Server
How to build the plugin on Unix/Linux
Under Unix, two libraries are available which support the TDS protocol:
- FreeTDS, a free implementation of the TDS protocol
(http://www.freetds.org). Note that FreeTDS is not yet stable,
so some functionality may not work as expected.
Regardless of which library you use, the shared object file
libsybdb.so is needed. Set the SYBASE environment variable to
point to the directory where you installed the client library and
execute qmake:
cd $QTDIR/plugins/src/sqldrivers/tds
qmake -o Makefile "INCLUDEPATH=$SYBASE/include" "LIBS=-L$SYBASE/lib -lsybdb"
make
How to build the plugin on Windows
You can either use the DB-Library supplied by Microsoft or the Sybase
Open Client (http://www.sybase.com). You must include NTWDBLIB.LIB to build the plugin:
cd %QTDIR%\plugins\src\sqldrivers\tds
qmake -o Makefile "LIBS+=NTWDBLIB.LIB" tds.pro
nmake
By default the Microsoft library is used on Windows, if you want to force
the use of the Sybase Open Client, you must define
Q_USE_SYBASE in %QTDIR%\src\sql\drivers\tds\qsql_tds.cpp.
Troubleshooting
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 COFF2OMF.EXE to convert libraries that have been
generated with Microsoft Visual C++.
If the compilation of a plugin succeeds but it cannot be loaded,
make sure that the following requirements are met:
Ensure that you are using a shared Qt library; you cannot use the
plugins with a static build.
Ensure that the environment variable QTDIR points to the right
directory. Go to the $QTDIR/plugins/sqldrivers directory and
make sure that the plugin exists in that directory.
Ensure that the client libraries of the DBMS are available on the
system. On Unix, run the command ldd and pass the name of the
plugin as parameter, for example ldd libqsqlmysql.so. 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.
How to write your own database driver
QSqlDatabase is responsible for loading and managing database driver
plugins. When a database is added (see QSqlDatabase::addDatabase()),
the appropriate driver plugin is loaded (using QSqlDriverPlugin).
QSqlDatabase relies on the driver plugin to provide interfaces for
QSqlDriver and QSqlResult.
QSqlDriver is an abstract base class which defines the functionality
of a SQL database driver. This includes functions such as
QSqlDriver::open() and QSqlDriver::close(). QSqlDriver is responsible
for connecting to a database, establish the proper environment, etc.
In addition, QSqlDriver can create QSqlQuery objects appropriate for
the particular database API. QSqlDatabase forwards many of its
function calls directly to QSqlDriver which provides the concrete
implementation.
QSqlResult is an abstract base class which defines the functionality
of a SQL database query. This includes statements such as SELECT,
UPDATE, and ALTER TABLE. 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 QSqlResult
which provides the concrete implementation.
QSqlDriver 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.
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
Q_EXPORT_PLUGIN macro. Read the Qt
Plugin 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 QTDIR/plugins/src/sqldrivers and
QTDIR/src/sql/drivers.
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