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| <title>6. Setting the SQL Join Syntax</title><base href="display"><link rel="stylesheet" type="text/css" href="css/docbook.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="manual.html" title="Apache OpenJPA 3.0 User's Guide"><link rel="up" href="ref_guide_dbsetup.html" title="Chapter 4. JDBC"><link rel="prev" href="ref_guide_dbsetup_isolation.html" title="5. Setting the Transaction Isolation"><link rel="next" href="ref_guide_dbsetup_multidb.html" title="7. Accessing Multiple Databases"></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">6. |
| Setting the SQL Join Syntax |
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| JDBC |
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| Setting the SQL Join Syntax |
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| <p> |
| Object queries often involve using SQL joins behind the scenes. You can |
| configure OpenJPA to use either SQL 92-style join syntax, in which joins are |
| placed in the SQL FROM clause, the traditional join syntax, in which join |
| criteria are part of the WHERE clause, or a database-specific join syntax |
| mandated by the <a class="link" href="ref_guide_dbsetup_dbsupport.html#ref_guide_dbsetup_dbdict" title="Example 4.7. Specifying a DBDictionary"><code class="classname"> |
| DBDictionary</code></a>. OpenJPA only supports outer joins when using |
| SQL 92 syntax or a database-specific syntax with outer join support. |
| </p> |
| <p> |
| The <a class="link" href="ref_guide_conf_jdbc.html#openjpa.jdbc.DBDictionary" title="6.2. openjpa.jdbc.DBDictionary"><code class="literal"> |
| openjpa.jdbc.DBDictionary</code></a> plugin accepts the <code class="literal"> |
| JoinSyntax</code> property to set the system's default syntax. The available |
| values are: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| <p> |
| <code class="literal">traditional</code>: Traditional SQL join syntax; outer joins are |
| not supported. |
| </p> |
| </li><li class="listitem"> |
| <p> |
| <code class="literal">database</code>: The database's native join syntax. Databases that |
| do not have a native syntax will default to one of the other options. |
| </p> |
| </li><li class="listitem"> |
| <p> |
| <code class="literal">sql92</code>: ANSI SQL92 join syntax. Outer joins are supported. |
| Not all databases support this syntax. |
| </p> |
| </li></ul></div> |
| <p> |
| You can change the join syntax at runtime through the OpenJPA fetch |
| configuration API, which is described in <a class="xref" href="ref_guide_runtime.html" title="Chapter 9. Runtime Extensions">Chapter 9, <i> |
| Runtime Extensions |
| </i></a>. |
| </p> |
| <div class="example" id="ref_guide_dbsetup_sql92_conf"><p class="title"><b>Example 4.9. |
| Specifying the Join Syntax Default |
| </b></p><div class="example-contents"> |
| |
| <pre class="programlisting"> |
| <property name="openjpa.jdbc.DBDictionary" value="JoinSyntax=sql92"/> |
| </pre> |
| </div></div><br class="example-break"> |
| <div class="example" id="ref_guide_dbsetup_sql92_fetch"><p class="title"><b>Example 4.10. |
| Specifying the Join Syntax at Runtime |
| </b></p><div class="example-contents"> |
| |
| <pre class="programlisting"> |
| import org.apache.openjpa.persistence.jdbc.*; |
| |
| ... |
| |
| Query q = em.createQuery("select m from Magazine m where m.title = 'JDJ'"); |
| OpenJPAQuery kq = OpenJPAPersistence.cast(q); |
| JDBCFetchPlan fetch = (JDBCFetchPlan) kq.getFetchPlan(); |
| fetch.setJoinSyntax(JoinSyntax.SQL92); |
| List results = q.getResultList(); |
| </pre> |
| </div></div><br class="example-break"> |
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| Setting the Transaction Isolation |
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| Accessing Multiple Databases |
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