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| <title>Chapter 12. SQL Queries</title><base href="display"><link rel="stylesheet" type="text/css" href="css/docbook.css"><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"><link rel="home" href="manual.html" title="Apache OpenJPA 2.4 User's Guide"><link rel="up" href="jpa_overview.html" title="Part 2. Java Persistence API"><link rel="prev" href="ch13s04.html" title="4. Generation of Canonical MetaModel classes"><link rel="next" href="jpa_overview_sqlquery_obj.html" title="2. Retrieving Persistent Objects with SQL"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 12. |
| SQL Queries |
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| SQL Queries |
| </h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="jpa_overview_sqlquery.html#jpa_overview_sqlquery_create">1. |
| Creating SQL Queries |
| </a></span></dt><dt><span class="section"><a href="jpa_overview_sqlquery_obj.html">2. |
| Retrieving Persistent Objects with SQL |
| </a></span></dt></dl></div> |
| |
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| <p> |
| JPQL is a powerful query language, but there are times when it is not enough. |
| Maybe you're migrating a JDBC application to JPA on a strict deadline, and you |
| don't have time to translate your existing SQL selects to JPQL. Or maybe a |
| certain query requires database-specific SQL your JPA implementation doesn't |
| support. Or maybe your DBA has spent hours crafting the perfect select statement |
| for a query in your application's critical path. Whatever the reason, SQL |
| queries can remain an essential part of an application. |
| </p> |
| <p> |
| You are probably familiar with executing SQL queries by obtaining a <code class="classname"> |
| java.sql.Connection</code>, using the JDBC APIs to create a <code class="classname"> |
| Statement</code>, and executing that <code class="classname">Statement</code> to |
| obtain a <code class="classname">ResultSet</code>. And of course, you are free to |
| continue using this low-level approach to SQL execution in your JPA |
| applications. However, JPA also supports executing SQL queries through the |
| <code class="classname">javax.persistence.Query</code> interface introduced in |
| <a class="xref" href="jpa_overview_query.html" title="Chapter 10. JPA Query">Chapter 10, <i> |
| JPA Query |
| </i></a>. Using a JPA SQL query, you can |
| retrieve either persistent objects or projections of column values. The |
| following sections detail each use. |
| </p> |
| <div class="section" title="1. Creating SQL Queries"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="jpa_overview_sqlquery_create">1. |
| Creating SQL Queries |
| </h2></div></div></div> |
| |
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| <p> |
| The <code class="classname">EntityManager</code> has two factory methods suitable for |
| creating SQL queries: |
| </p> |
| <pre class="programlisting"> |
| public Query createNativeQuery(String sqlString, Class resultClass); |
| public Query createNativeQuery(String sqlString, String resultSetMapping); |
| </pre> |
| <p> |
| The first method is used to create a new <code class="classname">Query</code> instance |
| that will return instances of the specified class. |
| </p> |
| <p> |
| The second method uses a <code class="literal">SqlResultSetMapping</code> to determine the |
| type of object or objects to return. The example below shows these methods in |
| action. |
| </p> |
| <div class="example"><a name="jpa_overview_sqlquery_createex"></a><p class="title"><b>Example 12.1. |
| Creating a SQL Query |
| </b></p><div class="example-contents"> |
| |
| <pre class="programlisting"> |
| EntityManager em = ...; |
| Query query = em.createNativeQuery("SELECT * FROM MAG", Magazine.class); |
| processMagazines(query.getResultList()); |
| </pre> |
| </div></div><br class="example-break"> |
| <div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3> |
| <p> |
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| In addition to SELECT statements, OpenJPA supports stored procedure invocations |
| as SQL queries. OpenJPA will assume any SQL that does not begin with the |
| <code class="literal">SELECT</code> keyword (ignoring case) is a stored procedure call, |
| and invoke it as such at the JDBC level. |
| </p> |
| </div> |
| </div> |
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