<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en_US" lang="en_US"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <!-- sql-programming.qdoc --> <title>Qt 4.8: Connecting to Databases</title> <link rel="stylesheet" type="text/css" href="style/style.css" /> <script src="scripts/jquery.js" type="text/javascript"></script> <script src="scripts/functions.js" type="text/javascript"></script> <link rel="stylesheet" type="text/css" href="style/superfish.css" /> <link rel="stylesheet" type="text/css" href="style/narrow.css" /> <!--[if IE]> <meta name="MSSmartTagsPreventParsing" content="true"> <meta http-equiv="imagetoolbar" content="no"> <![endif]--> <!--[if lt IE 7]> <link rel="stylesheet" type="text/css" href="style/style_ie6.css"> <![endif]--> <!--[if IE 7]> <link rel="stylesheet" type="text/css" href="style/style_ie7.css"> <![endif]--> <!--[if IE 8]> <link rel="stylesheet" type="text/css" href="style/style_ie8.css"> <![endif]--> <script src="scripts/superfish.js" type="text/javascript"></script> <script src="scripts/narrow.js" type="text/javascript"></script> </head> <body class="" onload="CheckEmptyAndLoadList();"> <div class="header" id="qtdocheader"> <div class="content"> <div id="nav-logo"> <a href="index.html">Home</a></div> <a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a> <div id="narrowsearch"></div> <div id="nav-topright"> <ul> <li class="nav-topright-home"><a href="http://qt.digia.com/">Qt HOME</a></li> <li class="nav-topright-dev"><a href="http://qt-project.org/">DEV</a></li> <li class="nav-topright-doc nav-topright-doc-active"><a href="http://qt-project.org/doc/"> DOC</a></li> <li class="nav-topright-blog"><a href="http://blog.qt.digia.com/">BLOG</a></li> </ul> </div> <div id="shortCut"> <ul> <li class="shortCut-topleft-inactive"><span><a href="index.html">Qt 4.8</a></span></li> <li class="shortCut-topleft-active"><a href="http://qt-project.org/doc/">ALL VERSIONS </a></li> </ul> </div> <ul class="sf-menu" id="narrowmenu"> <li><a href="#">API Lookup</a> <ul> <li><a href="classes.html">Class index</a></li> <li><a href="functions.html">Function index</a></li> <li><a href="modules.html">Modules</a></li> <li><a href="namespaces.html">Namespaces</a></li> <li><a href="qtglobal.html">Global Declarations</a></li> <li><a href="qdeclarativeelements.html">QML elements</a></li> </ul> </li> <li><a href="#">Qt Topics</a> <ul> <li><a href="qt-basic-concepts.html">Programming with Qt</a></li> <li><a href="qtquick.html">Device UIs & Qt Quick</a></li> <li><a href="qt-gui-concepts.html">UI Design with Qt</a></li> <li><a href="supported-platforms.html">Supported Platforms</a></li> <li><a href="technology-apis.html">Qt and Key Technologies</a></li> <li><a href="best-practices.html">How-To's and Best Practices</a></li> </ul> </li> <li><a href="#">Examples</a> <ul> <li><a href="all-examples.html">Examples</a></li> <li><a href="tutorials.html">Tutorials</a></li> <li><a href="demos.html">Demos</a></li> <li><a href="qdeclarativeexamples.html">QML Examples</a></li> </ul> </li> </ul> </div> </div> <div class="wrapper"> <div class="hd"> <span></span> </div> <div class="bd group"> <div class="sidebar"> <div class="searchlabel"> Search index:</div> <div class="search" id="sidebarsearch"> <form id="qtdocsearch" action="" onsubmit="return false;"> <fieldset> <input type="text" name="searchstring" id="pageType" value="" /> <div id="resultdialog"> <a href="#" id="resultclose">Close</a> <p id="resultlinks" class="all"><a href="#" id="showallresults">All</a> | <a href="#" id="showapiresults">API</a> | <a href="#" id="showarticleresults">Articles</a> | <a href="#" id="showexampleresults">Examples</a></p> <p id="searchcount" class="all"><span id="resultcount"></span><span id="apicount"></span><span id="articlecount"></span><span id="examplecount"></span> results:</p> <ul id="resultlist" class="all"> </ul> </div> </fieldset> </form> </div> <div class="box first bottombar" id="lookup"> <h2 title="API Lookup"><span></span> API Lookup</h2> <div id="list001" class="list"> <ul id="ul001" > <li class="defaultLink"><a href="classes.html">Class index</a></li> <li class="defaultLink"><a href="functions.html">Function index</a></li> <li class="defaultLink"><a href="modules.html">Modules</a></li> <li class="defaultLink"><a href="namespaces.html">Namespaces</a></li> <li class="defaultLink"><a href="qtglobal.html">Global Declarations</a></li> <li class="defaultLink"><a href="qdeclarativeelements.html">QML elements</a></li> </ul> </div> </div> <div class="box bottombar" id="topics"> <h2 title="Qt Topics"><span></span> Qt Topics</h2> <div id="list002" class="list"> <ul id="ul002" > <li class="defaultLink"><a href="qt-basic-concepts.html">Programming with Qt</a></li> <li class="defaultLink"><a href="qtquick.html">Device UIs & Qt Quick</a></li> <li class="defaultLink"><a href="qt-gui-concepts.html">UI Design with Qt</a></li> <li class="defaultLink"><a href="supported-platforms.html">Supported Platforms</a></li> <li class="defaultLink"><a href="technology-apis.html">Qt and Key Technologies</a></li> <li class="defaultLink"><a href="best-practices.html">How-To's and Best Practices</a></li> </ul> </div> </div> <div class="box" id="examples"> <h2 title="Examples"><span></span> Examples</h2> <div id="list003" class="list"> <ul id="ul003"> <li class="defaultLink"><a href="all-examples.html">Examples</a></li> <li class="defaultLink"><a href="tutorials.html">Tutorials</a></li> <li class="defaultLink"><a href="demos.html">Demos</a></li> <li class="defaultLink"><a href="qdeclarativeexamples.html">QML Examples</a></li> </ul> </div> </div> </div> <div class="wrap"> <div class="toolbar"> <div class="breadcrumb toolblock"> <ul> <li class="first"><a href="index.html">Home</a></li> <!-- Breadcrumbs go here --> <li>Connecting to Databases</li> </ul> </div> <div class="toolbuttons toolblock"> <ul> <li id="smallA" class="t_button">A</li> <li id="medA" class="t_button active">A</li> <li id="bigA" class="t_button">A</li> <li id="print" class="t_button"><a href="javascript:this.print();"> <span>Print</span></a></li> </ul> </div> </div> <div class="content mainContent"> <link rel="prev" href="sql-programming.html" /> <link rel="next" href="sql-sqlstatements.html" /> <p class="naviNextPrevious headerNavi"> <a class="prevPage" href="sql-programming.html">SQL Programming</a> <a class="nextPage" href="sql-sqlstatements.html">Executing SQL Statements</a> </p><p/> <h1 class="title">Connecting to Databases</h1> <span class="subtitle"></span> <!-- $$$sql-connecting.html-description --> <div class="descr"> <a name="details"></a> <p>To access a database with <a href="qsqlquery.html">QSqlQuery</a> or <a href="qsqlquerymodel.html">QSqlQueryModel</a>, create and open one or more database connections. Database connections are normally identified by connection name, <i>not</i> by database name. You can have multiple connections to the same database. <a href="qsqldatabase.html">QSqlDatabase</a> also supports the concept of a <i>default</i> connection, which is an unnamed connection. When calling <a href="qsqlquery.html">QSqlQuery</a> or <a href="qsqlquerymodel.html">QSqlQueryModel</a> member functions that take a connection name argument, if you don't pass a connection name, the default connection will be used. Creating a default connection is convenient when your application only requires one database connection.</p> <p>Note the difference between creating a connection and opening it. Creating a connection involves creating an instance of class <a href="qsqldatabase.html">QSqlDatabase</a>. The connection is not usable until it is opened. The following snippet shows how to create a <i>default</i> connection and then open it:</p> <pre class="cpp"> <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span> db <span class="operator">=</span> <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span><span class="operator">::</span>addDatabase(<span class="string">"QMYSQL"</span>); db<span class="operator">.</span>setHostName(<span class="string">"bigblue"</span>); db<span class="operator">.</span>setDatabaseName(<span class="string">"flightdb"</span>); db<span class="operator">.</span>setUserName(<span class="string">"acarlson"</span>); db<span class="operator">.</span>setPassword(<span class="string">"1uTbSbAs"</span>); <span class="type">bool</span> ok <span class="operator">=</span> db<span class="operator">.</span>open();</pre> <p>The first line creates the connection object, and the last line opens it for use. In between, we initialize some connection information, including the <a href="qsqldatabase.html#setDatabaseName">database name</a>, the <a href="qsqldatabase.html#setHostName">host name</a>, the <a href="qsqldatabase.html#setUserName">user name</a>, and the <a href="qsqldatabase.html#setPassword">password</a>. In this case, we are connecting to the MySQL database <tt>flightdb</tt> on the host <tt>bigblue</tt>. The <tt>"QMYSQL"</tt> argument to <a href="qsqldatabase.html#addDatabase">addDatabase()</a> specifies the type of database driver to use for the connection. The set of database drivers included with Qt are shown in the table of <a href="sql-driver.html#supported-databases">supported database drivers</a>.</p> <p>The connection in the snippet will be the <i>default</i> connection, because we don't pass the second argument to <a href="qsqldatabase.html#addDatabase">addDatabase()</a>, which is the connection name. For example, here we establish two MySQL database connections named <tt>"first"</tt> and <tt>"second"</tt>:</p> <pre class="cpp"> <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span> firstDB <span class="operator">=</span> <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span><span class="operator">::</span>addDatabase(<span class="string">"QMYSQL"</span><span class="operator">,</span> <span class="string">"first"</span>); <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span> secondDB <span class="operator">=</span> <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span><span class="operator">::</span>addDatabase(<span class="string">"QMYSQL"</span><span class="operator">,</span> <span class="string">"second"</span>);</pre> <p>After these connections have been initialized, <a href="qsqldatabase.html#open">open()</a> for each one to establish the live connections. If the <a href="qsqldatabase.html#open">open()</a> fails, it returns false. In that case, call <a href="qsqldatabase.html#lastError">QSqlDatabase::lastError</a>() to get error information.</p> <p>Once a connection is established, we can call the static function <a href="qsqldatabase.html#database">QSqlDatabase::database</a>() from anywhere with a connection name to get a pointer to that database connection. If we don't pass a connection name, it will return the default connection. For example:</p> <pre class="cpp"> <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span> defaultDB <span class="operator">=</span> <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span><span class="operator">::</span>database(); <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span> firstDB <span class="operator">=</span> <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span><span class="operator">::</span>database(<span class="string">"first"</span>); <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span> secondDB <span class="operator">=</span> <span class="type"><a href="qsqldatabase.html">QSqlDatabase</a></span><span class="operator">::</span>database(<span class="string">"second"</span>);</pre> <p>To remove a database connection, first close the database using <a href="qsqldatabase.html#close">QSqlDatabase::close</a>(), then remove it using the static method <a href="qsqldatabase.html#removeDatabase">QSqlDatabase::removeDatabase</a>().</p> </div> <!-- @@@sql-connecting.html --> <p class="naviNextPrevious footerNavi"> <a class="prevPage" href="sql-programming.html">SQL Programming</a> <a class="nextPage" href="sql-sqlstatements.html">Executing SQL Statements</a> </p> </div> </div> </div> <div class="ft"> <span></span> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2013 Digia Plc and/or its subsidiaries. Documentation contributions included herein are the copyrights of their respective owners.</p> <br /> <p> The documentation provided herein is licensed under the terms of the <a href="http://www.gnu.org/licenses/fdl.html">GNU Free Documentation License version 1.3</a> as published by the Free Software Foundation.</p> <p> Documentation sources may be obtained from <a href="http://www.qt-project.org"> www.qt-project.org</a>.</p> <br /> <p> Digia, Qt and their respective logos are trademarks of Digia Plc in Finland and/or other countries worldwide. All other trademarks are property of their respective owners. <a title="Privacy Policy" href="http://en.gitorious.org/privacy_policy/">Privacy Policy</a></p> </div> <script src="scripts/functions.js" type="text/javascript"></script> </body> </html>