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41
42/*!
43 \page qt4-sql.html
44 \title The Qt 4 Database GUI Layer
45
46 \contentspage {What's New in Qt 4}{Home}
47 \previouspage Cross-Platform Accessibility Support in Qt 4
48 \nextpage The Network Module in Qt 4
49
50 The GUI layer of the SQL module in Qt 4 has been entirely
51 redesigned to work with \l{qt4-interview.html}{Interview} (Qt's
52 new model/view classes). It consists of three model classes
53 (QSqlQueryModel, QSqlTableModel, and QSqlRelationalTableModel)
54 that can be used with Qt's view classes, notably QTableView.
55
56 \section1 General Overview
57
58 The Qt 4 SQL classes are divided into three layers:
59
60 \list
61 \o The database drivers
62 \o The core SQL classes
63 \o The GUI classes
64 \endlist
65
66 The database drivers and the core SQL classes are mostly the same
67 as in Qt 3. The database item models are new with Qt 4; they
68 inherit from QAbstractItemModel and make it easy to present data
69 from a database in a view class such as QListView, QTableView,
70 and QTreeView.
71
72 The philosophy behind the Qt 4 SQL module is that it should be
73 possible to use database models for rendering and editing data
74 just like any other item models. By changing the model at
75 run-time, you can decide whether you want to store your data in
76 an SQL database or in, say, an XML file. This generic approach
77 has the additional benefit that you don't need to know anything
78 about SQL to display and edit data.
79
80 The Qt 4 SQL module includes three item models:
81
82 \list
83 \o QSqlQueryModel is a read-only model based on an arbitrary
84 SQL query.
85 \o QSqlTableModel is a read-write model that works on a single
86 table.
87 \o QSqlRelationalTableModel is a QSqlTableModel subclass with
88 foreign key support.
89 \endlist
90
91 Combined with Qt's view classes and Qt's default delegate class
92 (QItemDelegate), the models offer a very powerful mechanism for
93 accessing databases. For finer control on the rendering of the
94 fields, you can subclass one of the predefined models, or even
95 QAbstractItemDelegate or QItemDelegate if you need finer control.
96
97 You can also perform some customizations without subclassing. For
98 example, you can sort a table using QSqlTableModel::sort(), and
99 you can initialize new rows by connecting to the
100 QSqlTableModel::primeInsert() signal.
101
102 One nice feature supported by the read-write models is the
103 possibility to perform changes to the item model without
104 affecting the database until QSqlTableModel::submitAll() is
105 called. Changes can be dropped using QSqlTableModel::revertAll().
106
107 The new classes perform advantageously compared to the SQL
108 module's GUI layer in Qt 3. Speed and memory improvements in the
109 tool classes (especially QVariant, QString, and QMap) and in the
110 SQL drivers contribute to making Qt 4 database applications more
111 snappy.
112
113 See the \l QtSql module overview for a more complete introduction
114 to Qt's SQL classes.
115
116 \section1 Example Code
117
118 The simplest way to present data from a database is to simply
119 combine a QSqlQueryModel with a QTableView:
120
121 \snippet doc/src/snippets/code/doc_src_qt4-sql.qdoc 0
122
123 To present the contents of a single table, we can use
124 QSqlTableModel instead:
125
126 \snippet doc/src/snippets/code/doc_src_qt4-sql.qdoc 1
127
128 In practice, it's common that we need to customize the rendering
129 of a field in the database. In that case, we can create our own
130 model based on QSqlQueryModel. The next code snippet shows a
131 custom model that prepends '#' to the value in field 0 and
132 converts the value in field 2 to uppercase:
133
134 \snippet examples/sql/querymodel/customsqlmodel.h 0
135 \codeline
136 \snippet examples/sql/querymodel/customsqlmodel.cpp 0
137
138 It is also possible to subclass QSqlQueryModel to add support for
139 editing. This is done by reimplementing
140 QAbstractItemModel::flags() to specify which database fields are
141 editable and QAbstractItemModel::setData() to modify the
142 database. Here's an example of a setData() reimplementation that
143 changes the first or last name of a person:
144
145 \snippet examples/sql/querymodel/editablesqlmodel.cpp 1
146
147 It relies on helper functions called \c setFirstName() and
148 \c setLastName(), which execute an \c{update}. Here's
149 \c setFirstName():
150
151 \snippet examples/sql/querymodel/editablesqlmodel.cpp 2
152
153 See Qt's \c examples/sql directory for more examples.
154
155 \section1 Comparison with Qt 3
156
157 The core SQL database classes haven't changed so much since Qt 3.
158 Here's a list of the main changes:
159
160 \list
161 \o QSqlDatabase is now value-based instead of pointer-based.
162 \o QSqlFieldInfo and QSqlRecordInfo has been merged into
163 QSqlField and QSqlRecord.
164 \o The SQL query generation has been moved into the drivers. This
165 makes it possible to use non-standard SQL extensions. It also
166 opens the door to non-SQL databases.
167 \endlist
168
169 The GUI-related database classes have been entirely redesigned.
170 The QSqlCursor abstraction has been replaced with QSqlQueryModel
171 and QSqlTableModel; QSqlEditorFactory is replaced by
172 QAbstractItemDelegate; QDataTable is replaced by QTableView. The
173 old classes are part of the \l{Qt3Support} library to aid
174 porting to Qt 4.
175*/
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