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diff --git a/doc/src/porting/qt4-sql.qdoc b/doc/src/porting/qt4-sql.qdoc new file mode 100644 index 0000000..2a5a206 --- /dev/null +++ b/doc/src/porting/qt4-sql.qdoc @@ -0,0 +1,161 @@ +/**************************************************************************** +** +** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies). +** All rights reserved. +** Contact: Nokia Corporation (qt-info@nokia.com) +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:FDL$ +** No Commercial Usage +** This file contains pre-release code and may not be distributed. +** You may use this file in accordance with the terms and conditions +** contained in the Technology Preview License Agreement accompanying +** this package. +** +** GNU Free Documentation License +** Alternatively, this file may be used under the terms of the GNU Free +** Documentation License version 1.3 as published by the Free Software +** Foundation and appearing in the file included in the packaging of this +** file. +** +** If you have questions regarding the use of this file, please contact +** Nokia at qt-info@nokia.com. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \page qt4-sql.html + \title The Qt 4 Database GUI Layer + + \contentspage {What's New in Qt 4}{Home} + \previouspage Cross-Platform Accessibility Support in Qt 4 + \nextpage The Network Module in Qt 4 + + The GUI layer of the SQL module in Qt 4 has been entirely + redesigned to work with \l{qt4-interview.html}{Interview} (Qt's + new model/view classes). It consists of three model classes + (QSqlQueryModel, QSqlTableModel, and QSqlRelationalTableModel) + that can be used with Qt's view classes, notably QTableView. + + \section1 General Overview + + The Qt 4 SQL classes are divided into three layers: + + \list + \o The database drivers + \o The core SQL classes + \o The GUI classes + \endlist + + The database drivers and the core SQL classes are mostly the same + as in Qt 3. The database item models are new with Qt 4; they + inherit from QAbstractItemModel and make it easy to present data + from a database in a view class such as QListView, QTableView, + and QTreeView. + + The philosophy behind the Qt 4 SQL module is that it should be + possible to use database models for rendering and editing data + just like any other item models. By changing the model at + run-time, you can decide whether you want to store your data in + an SQL database or in, say, an XML file. This generic approach + has the additional benefit that you don't need to know anything + about SQL to display and edit data. + + The Qt 4 SQL module includes three item models: + + \list + \o QSqlQueryModel is a read-only model based on an arbitrary + SQL query. + \o QSqlTableModel is a read-write model that works on a single + table. + \o QSqlRelationalTableModel is a QSqlTableModel subclass with + foreign key support. + \endlist + + Combined with Qt's view classes and Qt's default delegate class + (QItemDelegate), the models offer a very powerful mechanism for + accessing databases. For finer control on the rendering of the + fields, you can subclass one of the predefined models, or even + QAbstractItemDelegate or QItemDelegate if you need finer control. + + You can also perform some customizations without subclassing. For + example, you can sort a table using QSqlTableModel::sort(), and + you can initialize new rows by connecting to the + QSqlTableModel::primeInsert() signal. + + One nice feature supported by the read-write models is the + possibility to perform changes to the item model without + affecting the database until QSqlTableModel::submitAll() is + called. Changes can be dropped using QSqlTableModel::revertAll(). + + The new classes perform advantageously compared to the SQL + module's GUI layer in Qt 3. Speed and memory improvements in the + tool classes (especially QVariant, QString, and QMap) and in the + SQL drivers contribute to making Qt 4 database applications more + snappy. + + See the \l QtSql module overview for a more complete introduction + to Qt's SQL classes. + + \section1 Example Code + + The simplest way to present data from a database is to simply + combine a QSqlQueryModel with a QTableView: + + \snippet doc/src/snippets/code/doc_src_qt4-sql.cpp 0 + + To present the contents of a single table, we can use + QSqlTableModel instead: + + \snippet doc/src/snippets/code/doc_src_qt4-sql.cpp 1 + + In practice, it's common that we need to customize the rendering + of a field in the database. In that case, we can create our own + model based on QSqlQueryModel. The next code snippet shows a + custom model that prepends '#' to the value in field 0 and + converts the value in field 2 to uppercase: + + \snippet examples/sql/querymodel/customsqlmodel.h 0 + \codeline + \snippet examples/sql/querymodel/customsqlmodel.cpp 0 + + It is also possible to subclass QSqlQueryModel to add support for + editing. This is done by reimplementing + QAbstractItemModel::flags() to specify which database fields are + editable and QAbstractItemModel::setData() to modify the + database. Here's an example of a setData() reimplementation that + changes the first or last name of a person: + + \snippet examples/sql/querymodel/editablesqlmodel.cpp 1 + + It relies on helper functions called \c setFirstName() and + \c setLastName(), which execute an \c{update}. Here's + \c setFirstName(): + + \snippet examples/sql/querymodel/editablesqlmodel.cpp 2 + + See Qt's \c examples/sql directory for more examples. + + \section1 Comparison with Qt 3 + + The core SQL database classes haven't changed so much since Qt 3. + Here's a list of the main changes: + + \list + \o QSqlDatabase is now value-based instead of pointer-based. + \o QSqlFieldInfo and QSqlRecordInfo has been merged into + QSqlField and QSqlRecord. + \o The SQL query generation has been moved into the drivers. This + makes it possible to use non-standard SQL extensions. It also + opens the door to non-SQL databases. + \endlist + + The GUI-related database classes have been entirely redesigned. + The QSqlCursor abstraction has been replaced with QSqlQueryModel + and QSqlTableModel; QSqlEditorFactory is replaced by + QAbstractItemDelegate; QDataTable is replaced by QTableView. The + old classes are part of the \l{Qt3Support} library to aid + porting to Qt 4. +*/ |