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<h1 class="title">Presenting Data in a Table View</h1>
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<p>The <a href="qsqlquerymodel.html">QSqlQueryModel</a>, <a href="qsqltablemodel.html">QSqlTableModel</a>, and <a href="qsqlrelationaltablemodel.html">QSqlRelationalTableModel</a> classes can be used as a data source for Qt's view classes such as <a href="qlistview.html">QListView</a>, <a href="qtableview.html">QTableView</a>, and <a href="qtreeview.html">QTreeView</a>. In practice, <a href="qtableview.html">QTableView</a> is by far the most common choice, because an SQL result set is essentially a two-dimensional data structure.</p>
<p class="centerAlign"><img src="images/relationaltable.png" alt="A table view displaying a QSqlTableModel" /></p><p>The following example creates a view based on an SQL data model:</p>
<pre class="cpp"> <span class="type"><a href="qtableview.html">QTableView</a></span> <span class="operator">*</span>view <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtableview.html">QTableView</a></span>;
view<span class="operator">-</span><span class="operator">></span>setModel(model);
view<span class="operator">-</span><span class="operator">></span>show();</pre>
<p>If the model is a read-write model (e.g., <a href="qsqltablemodel.html">QSqlTableModel</a>), the view lets the user edit the fields. You can disable this by calling</p>
<pre class="cpp"> view<span class="operator">-</span><span class="operator">></span>setEditTriggers(<span class="type"><a href="qabstractitemview.html">QAbstractItemView</a></span><span class="operator">::</span>NoEditTriggers);</pre>
<p>You can use the same model as a data source for multiple views. If the user edits the model through one of the views, the other views will reflect the changes immediately. The <a href="sql-tablemodel.html">Table Model</a> example shows how it works.</p>
<p>View classes display a header at the top to label the columns. To change the header texts, call <a href="qabstractitemmodel.html#setHeaderData">setHeaderData()</a> on the model. The header's labels default to the table's field names. For example:</p>
<pre class="cpp"> model<span class="operator">-</span><span class="operator">></span>setHeaderData(<span class="number">0</span><span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>Horizontal<span class="operator">,</span> <span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>tr(<span class="string">"ID"</span>));
model<span class="operator">-</span><span class="operator">></span>setHeaderData(<span class="number">1</span><span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>Horizontal<span class="operator">,</span> <span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>tr(<span class="string">"Name"</span>));
model<span class="operator">-</span><span class="operator">></span>setHeaderData(<span class="number">2</span><span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>Horizontal<span class="operator">,</span> <span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>tr(<span class="string">"City"</span>));
model<span class="operator">-</span><span class="operator">></span>setHeaderData(<span class="number">3</span><span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>Horizontal<span class="operator">,</span> <span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>tr(<span class="string">"Country"</span>));</pre>
<p><a href="qtableview.html">QTableView</a> also has a vertical header on the left with numbers identifying the rows. If you insert rows programmatically using <a href="qsqltablemodel.html#insertRows">QSqlTableModel::insertRows</a>(), the new rows will be marked with an asterisk (*) until they are submitted using <a href="qsqltablemodel.html#submitAll">submitAll()</a> or automatically when the user moves to another record (assuming the <a href="qsqltablemodel.html#EditStrategy-enum">edit strategy</a> is <a href="qsqltablemodel.html#EditStrategy-enum">QSqlTableModel::OnRowChange</a>).</p>
<p class="centerAlign"><img src="images/insertrowinmodelview.png" alt="Inserting a row in a model" /></p><p>Likewise, if you remove rows using <a href="qsqltablemodel.html#removeRows">removeRows()</a>, the rows will be marked with an exclamation mark (!) until the change is submitted.</p>
<p>The items in the view are rendered using a delegate. The default delegate, <a href="qitemdelegate.html">QItemDelegate</a>, handles the most common data types (<tt>int</tt>, <a href="qstring.html">QString</a>, <a href="qimage.html">QImage</a>, etc.). The delegate is also responsible for providing editor widgets (e.g., a combobox) when the user starts editing an item in the view. You can create your own delegates by subclassing <a href="qabstractitemdelegate.html">QAbstractItemDelegate</a> or <a href="qitemdelegate.html">QItemDelegate</a>. See <a href="model-view-programming.html">Model/View Programming</a> for more information.</p>
<p><a href="qsqltablemodel.html">QSqlTableModel</a> is optimized to operate on a single table at a time. If you need a read-write model that operates on an arbitrary result set, you can subclass <a href="qsqlquerymodel.html">QSqlQueryModel</a> and reimplement <a href="qabstractitemmodel.html#flags">flags()</a> and <a href="qabstractitemmodel.html#setData">setData()</a> to make it read-write. The following two functions make fields 1 and 2 of a query model editable:</p>
<pre class="cpp"> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>ItemFlags EditableSqlModel<span class="operator">::</span>flags(
<span class="keyword">const</span> <span class="type"><a href="qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index) <span class="keyword">const</span>
{
<span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>ItemFlags flags <span class="operator">=</span> <span class="type"><a href="qsqlquerymodel.html">QSqlQueryModel</a></span><span class="operator">::</span>flags(index);
<span class="keyword">if</span> (index<span class="operator">.</span>column() <span class="operator">=</span><span class="operator">=</span> <span class="number">1</span> <span class="operator">|</span><span class="operator">|</span> index<span class="operator">.</span>column() <span class="operator">=</span><span class="operator">=</span> <span class="number">2</span>)
flags <span class="operator">|</span><span class="operator">=</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>ItemIsEditable;
<span class="keyword">return</span> flags;
}
<span class="type">bool</span> EditableSqlModel<span class="operator">::</span>setData(<span class="keyword">const</span> <span class="type"><a href="qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qvariant.html">QVariant</a></span> <span class="operator">&</span>value<span class="operator">,</span> <span class="type">int</span> <span class="comment">/* role */</span>)
{
<span class="keyword">if</span> (index<span class="operator">.</span>column() <span class="operator"><</span> <span class="number">1</span> <span class="operator">|</span><span class="operator">|</span> index<span class="operator">.</span>column() <span class="operator">></span> <span class="number">2</span>)
<span class="keyword">return</span> <span class="keyword">false</span>;
<span class="type"><a href="qmodelindex.html">QModelIndex</a></span> primaryKeyIndex <span class="operator">=</span> <span class="type"><a href="qsqlquerymodel.html">QSqlQueryModel</a></span><span class="operator">::</span>index(index<span class="operator">.</span>row()<span class="operator">,</span> <span class="number">0</span>);
<span class="type">int</span> id <span class="operator">=</span> data(primaryKeyIndex)<span class="operator">.</span>toInt();
clear();
<span class="type">bool</span> ok;
<span class="keyword">if</span> (index<span class="operator">.</span>column() <span class="operator">=</span><span class="operator">=</span> <span class="number">1</span>) {
ok <span class="operator">=</span> setFirstName(id<span class="operator">,</span> value<span class="operator">.</span>toString());
} <span class="keyword">else</span> {
ok <span class="operator">=</span> setLastName(id<span class="operator">,</span> value<span class="operator">.</span>toString());
}
refresh();
<span class="keyword">return</span> ok;
}</pre>
<p>The setFirstName() helper function is defined as follows:</p>
<pre class="cpp"> <span class="type">bool</span> EditableSqlModel<span class="operator">::</span>setFirstName(<span class="type">int</span> personId<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>firstName)
{
<span class="type"><a href="qsqlquery.html">QSqlQuery</a></span> query;
query<span class="operator">.</span>prepare(<span class="string">"update person set firstname = ? where id = ?"</span>);
query<span class="operator">.</span>addBindValue(firstName);
query<span class="operator">.</span>addBindValue(personId);
<span class="keyword">return</span> query<span class="operator">.</span>exec();
}</pre>
<p>The setLastName() function is similar. See the <a href="sql-querymodel.html">Query Model</a> example for the complete source code.</p>
<p>Subclassing a model makes it possible to customize it in many ways: You can provide tooltips for the items, change the background color, provide calculated values, provide different values for viewing and editing, handle null values specially, and more. See <a href="model-view-programming.html">Model/View Programming</a> as well as the <a href="qabstractitemview.html">QAbstractItemView</a> reference documentation for details.</p>
<p>If all you need is to resolve a foreign key to a more human-friendly string, you can use <a href="qsqlrelationaltablemodel.html">QSqlRelationalTableModel</a>. For best results, you should also use <a href="qsqlrelationaldelegate.html">QSqlRelationalDelegate</a>, a delegate that provides combobox editors for editing foreign keys.</p>
<p class="centerAlign"><img src="images/relationaltable.png" alt="Editing a foreign key in a relational table" /></p><p>The <a href="sql-relationaltablemodel.html">Relational Table Model</a> example illustrates how to use <a href="qsqlrelationaltablemodel.html">QSqlRelationalTableModel</a> in conjunction with <a href="qsqlrelationaldelegate.html">QSqlRelationalDelegate</a> to provide tables with foreign key support.</p>
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