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<div class="title">Making queries </div> </div>
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<div class="textblock"><p>The <a class="el" href="classQDjango.html" title="The QDjango class provides a set of static functions.">QDjango</a> object relational mapper (ORM) supports the concept of querysets, borrowed from django's ORM.</p>
<p>A queryset is a collection of database objects which match a certain number of user-specified conditions.</p>
<p>You can learn more about querysets by reading the <a class="el" href="classQDjangoQuerySet.html" title="The QDjangoQuerySet class is a template class for performing database queries.">QDjangoQuerySet</a> template class documentation.</p>
<h2><a class="anchor" id="creating-queries"></a>
Creating and filtering querysets</h2>
<p>Before you can start using querysets, you need to declare your database models as described in <a class="el" href="models.html">Database models</a>.</p>
<p>The most basic queryset matches all the objects for a given model.</p>
<div class="fragment"><pre class="fragment"><span class="comment">// all users</span>
<a class="code" href="classQDjangoQuerySet.html" title="The QDjangoQuerySet class is a template class for performing database queries.">QDjangoQuerySet<User></a> users;
</pre></div><p>You can use the <a class="el" href="classQDjangoQuerySet.html#a5fc458cda1b34cad3d9f4f99224feae6">QDjangoQuerySet::filter()</a> and <a class="el" href="classQDjangoQuerySet.html#af27220e6645f081348c99ff55a5d5ed6">QDjangoQuerySet::exclude()</a> methods to add filtering conditions to a querset:</p>
<div class="fragment"><pre class="fragment"><span class="comment">// find all users whose password is "foo" and whose username is not "bar"</span>
<a class="code" href="classQDjangoQuerySet.html" title="The QDjangoQuerySet class is a template class for performing database queries.">QDjangoQuerySet<User></a> someUsers;
someUsers = users.<a class="code" href="classQDjangoQuerySet.html#a5fc458cda1b34cad3d9f4f99224feae6">filter</a>(<a class="code" href="classQDjangoWhere.html" title="The QDjangoWhere class expresses an SQL constraint.">QDjangoWhere</a>(<span class="stringliteral">"password"</span>, <a class="code" href="classQDjangoWhere.html#acd1b7a7d3e2367c6f4846dd9f0ebbd61a7fe62ab85b26467aca41c4b4307a6a45">QDjangoWhere::Equals</a>, <span class="stringliteral">"foo"</span>) &&
<a class="code" href="classQDjangoWhere.html" title="The QDjangoWhere class expresses an SQL constraint.">QDjangoWhere</a>(<span class="stringliteral">"username"</span>, <a class="code" href="classQDjangoWhere.html#acd1b7a7d3e2367c6f4846dd9f0ebbd61a1a733f4d536e1a12ca5cfb791e00ed8c">QDjangoWhere::NotEquals</a>, <span class="stringliteral">"bar"</span>));
<span class="comment">// find all users whose username is "foo" or "bar"</span>
someUsers = users.<a class="code" href="classQDjangoQuerySet.html#a5fc458cda1b34cad3d9f4f99224feae6">filter</a>(<a class="code" href="classQDjangoWhere.html" title="The QDjangoWhere class expresses an SQL constraint.">QDjangoWhere</a>(<span class="stringliteral">"username"</span>, <a class="code" href="classQDjangoWhere.html#acd1b7a7d3e2367c6f4846dd9f0ebbd61a7fe62ab85b26467aca41c4b4307a6a45">QDjangoWhere::Equals</a>, <span class="stringliteral">"foo"</span>) ||
<a class="code" href="classQDjangoWhere.html" title="The QDjangoWhere class expresses an SQL constraint.">QDjangoWhere</a>(<span class="stringliteral">"username"</span>, <a class="code" href="classQDjangoWhere.html#acd1b7a7d3e2367c6f4846dd9f0ebbd61a7fe62ab85b26467aca41c4b4307a6a45">QDjangoWhere::Equals</a>, <span class="stringliteral">"bar"</span>));
<span class="comment">// find all users whose username starts with "f":</span>
someUsers = users.<a class="code" href="classQDjangoQuerySet.html#a5fc458cda1b34cad3d9f4f99224feae6">filter</a>(<a class="code" href="classQDjangoWhere.html" title="The QDjangoWhere class expresses an SQL constraint.">QDjangoWhere</a>(<span class="stringliteral">"username"</span>, <a class="code" href="classQDjangoWhere.html#acd1b7a7d3e2367c6f4846dd9f0ebbd61a2c59d066559ebd6ebd37d65f9ac33622">QDjangoWhere::StartsWith</a>, <span class="stringliteral">"f"</span>));
</pre></div><p>You can also use the <a class="el" href="classQDjangoQuerySet.html#af353175373ce8a2087ed42840be58f4c">QDjangoQuerySet::limit()</a> method to limit the number of returned rows:</p>
<div class="fragment"><pre class="fragment"><span class="comment">// limit number of results</span>
someUsers = users.<a class="code" href="classQDjangoQuerySet.html#af353175373ce8a2087ed42840be58f4c">limit</a>(0, 100);
</pre></div><h2><a class="anchor" id="iterating-queries"></a>
Iterating over results</h2>
<p>The easiest way to iterate over results is to use Qt's <a href="http://doc.qt.nokia.com/latest/containers.html#the-foreach-keyword">foreach</a> keyword:</p>
<div class="fragment"><pre class="fragment"><span class="comment">// iterate over matching users</span>
<span class="keywordflow">foreach</span> (<span class="keyword">const</span> User &user, someUsers) {
qDebug() << <span class="stringliteral">"found user"</span> << user.username;
}
</pre></div><p>Another way of iterating over results is to run over model instances using the <a class="el" href="classQDjangoQuerySet.html#a90a5cd47b75e0cee952461ab574b3f46">QDjangoQuerySet::size()</a> and <a class="el" href="classQDjangoQuerySet.html#a1bcfbffb6676f4ec19f9278c3f0adf4f">QDjangoQuerySet::at()</a> methods:</p>
<div class="fragment"><pre class="fragment"><span class="comment">// iterate over matching users</span>
User user;
<span class="keywordflow">for</span> (<span class="keywordtype">int</span> i = 0; i < someUsers.<a class="code" href="classQDjangoQuerySet.html#a90a5cd47b75e0cee952461ab574b3f46">size</a>(); ++i) {
<span class="keywordflow">if</span> (someUsers.<a class="code" href="classQDjangoQuerySet.html#a1bcfbffb6676f4ec19f9278c3f0adf4f">at</a>(i, &user)) {
qDebug() << <span class="stringliteral">"found user"</span> << user.username;
}
}
</pre></div><p>It is also possible to retrieve field data without creating model instances using the <a class="el" href="classQDjangoQuerySet.html#a9e558d61d83f171a3e627295d544ccb1">QDjangoQuerySet::values()</a> and <a class="el" href="classQDjangoQuerySet.html#a7125a4bf5e722c8af322c1b6e4be05b0">QDjangoQuerySet::valuesList()</a> methods:</p>
<div class="fragment"><pre class="fragment"><span class="comment">// retrieve usernames and passwords for matching users as maps</span>
QList<QVariantMap> propertyMaps = someUsers.<a class="code" href="classQDjangoQuerySet.html#a9e558d61d83f171a3e627295d544ccb1">values</a>(QStringList() << <span class="stringliteral">"username"</span> << <span class="stringliteral">"password"</span>);
<span class="keywordflow">foreach</span> (<span class="keyword">const</span> QVariantMap &propertyMap, propertyMaps) {
qDebug() << <span class="stringliteral">"username"</span> << propertyList[<span class="stringliteral">"username"</span>];
qDebug() << <span class="stringliteral">"password"</span> << propertyList[<span class="stringliteral">"password"</span>];
}
<span class="comment">// retrieve usernames and passwords for matching users as lists</span>
QList<QVariantList> propertyLists = someUsers.<a class="code" href="classQDjangoQuerySet.html#a7125a4bf5e722c8af322c1b6e4be05b0">valuesList</a>(QStringList() << <span class="stringliteral">"username"</span> << <span class="stringliteral">"password"</span>);
<span class="keywordflow">foreach</span> (<span class="keyword">const</span> QVariantList &propertyList, propertyLists) {
qDebug() << <span class="stringliteral">"username"</span> << propertyList[0];
qDebug() << <span class="stringliteral">"password"</span> << propertyList[1];
}
</pre></div><h2><a class="anchor" id="other-queries"></a>
Other operations</h2>
<div class="fragment"><pre class="fragment"><span class="comment">// count matching users without retrieving their data</span>
<span class="keywordtype">int</span> numberOfUsers = someUsers.<a class="code" href="classQDjangoQuerySet.html#a90bfd4aecf07372b2d68c56b345e12a8">count</a>();
<span class="comment">// delete all the users in the queryset</span>
someUsers.<a class="code" href="classQDjangoQuerySet.html#ad174f57f5b4091aeba43482ac3b0635f">remove</a>();
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