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| <title>2. Additional JPA Metadata</title><link rel="stylesheet" href="css/docbook.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.72.0"><link rel="start" href="manual.html" title="Apache OpenJPA User's Guide"><link rel="up" href="ref_guide_meta.html" title="Chapter 6. Metadata"><link rel="prev" href="ref_guide_meta.html" title="Chapter 6. Metadata"><link rel="next" href="ref_guide_meta_ext.html" title="3. Metadata Extensions"></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">2. |
| Additional JPA Metadata |
| </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ref_guide_meta.html">Prev</a> </td><th width="60%" align="center">Chapter 6. |
| Metadata |
| </th><td width="20%" align="right"> <a accesskey="n" href="ref_guide_meta_ext.html">Next</a></td></tr></table><hr></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ref_guide_meta_jpa"></a>2. |
| Additional JPA Metadata |
| </h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="ref_guide_meta_jpa.html#ref_guide_meta_jpa_datastoreid">2.1. |
| Datastore Identity |
| </a></span></dt><dt><span class="section"><a href="ref_guide_meta_jpa.html#ref_guide_meta_jpa_version">2.2. |
| Surrogate Version |
| </a></span></dt><dt><span class="section"><a href="ref_guide_meta_jpa.html#ref_guide_meta_jpa_persistent">2.3. |
| Persistent Field Values |
| </a></span></dt><dt><span class="section"><a href="ref_guide_meta_jpa.html#ref_guide_meta_jpa_persistent_coll">2.4. Persistent Collection Fields</a></span></dt><dt><span class="section"><a href="ref_guide_meta_jpa.html#ref_guide_meta_jpa_persistent_map">2.5. Persistent Map Fields</a></span></dt></dl></div><a class="indexterm" name="d0e23950"></a><p> |
| This section describes OpenJPA's core additions to standard entity metadata. We |
| present the object-relational mapping syntax to support these additions in |
| <a href="ref_guide_mapping_jpa.html" title="7. Additional JPA Mappings">Section 7, “ |
| Additional JPA Mappings |
| ”</a>. Finally, |
| <a href="ref_guide_meta_ext.html" title="3. Metadata Extensions">Section 3, “ |
| Metadata Extensions |
| ”</a> covers additional extensions to JPA |
| metadata that allow you to access auxiliary OpenJPA features. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="ref_guide_meta_jpa_datastoreid"></a>2.1. |
| Datastore Identity |
| </h3></div></div></div><a class="indexterm" name="d0e23964"></a><p> |
| JPA typically requires you to declare one or more <code class="literal">Id</code> fields |
| to act as primary keys. OpenJPA, however, can create and maintain a surrogate |
| primary key value when you do not declare any <code class="literal">Id</code> fields. This |
| form of persistent identity is called <span class="emphasis"><em>datastore identity</em></span>. |
| <a href="ref_guide_pc_oid.html" title="4. Object Identity">Section 4, “ |
| Object Identity |
| ”</a> discusses OpenJPA's support for |
| datastore identity in JPA. We cover how to map your datastore identity primary |
| key column in <a href="ref_guide_mapping_jpa.html#ref_guide_mapping_jpa_datastoreid" title="7.1. Datastore Identity Mapping">Section 7.1, “ |
| Datastore Identity Mapping |
| ”</a> |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="ref_guide_meta_jpa_version"></a>2.2. |
| Surrogate Version |
| </h3></div></div></div><a class="indexterm" name="d0e23987"></a><p> |
| Just as OpenJPA can maintain your entity's identity without any <code class="literal">Id |
| </code> fields, OpenJPA can maintain your entity's optimistic version without |
| any <code class="literal">Version</code> fields. |
| <a href="ref_guide_mapping_jpa.html#ref_guide_mapping_jpa_version" title="7.2. Surrogate Version Mapping">Section 7.2, “ |
| Surrogate Version Mapping |
| ”</a> shows you how to map |
| surrogate version columns. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="ref_guide_meta_jpa_persistent"></a>2.3. |
| Persistent Field Values |
| </h3></div></div></div><a class="indexterm" name="d0e24005"></a><p> |
| JPA defines <code class="literal">Basic</code>, <code class="literal">Lob</code>, <code class="literal">Embedded |
| </code>, <code class="literal">ManyToOne</code>, and <code class="literal">OneToOne</code> |
| persistence strategies for direct field values. OpenJPA supports all of these |
| standard strategies, but adds one of its own: <code class="literal">Persistent</code>. |
| The <a xmlns:xlink="http://www.w3.org/1999/xlink" href="../javadoc/org/apache/openjpa/persistence/Persistent.html" target="_top"> |
| <code class="classname">org.apache.openjpa.persistence.Persistent</code></a> |
| metadata annotation can represent any direct field value, including custom |
| types. It has the following properties: |
| </p><div class="itemizedlist"><ul type="disc"><li><p> |
| <code class="literal">FetchType fetch</code>: Whether to load the field eagerly or |
| lazily. Corresponds exactly to the same-named property of standard JPA |
| annotations such as <a href="jpa_overview_meta_field.html#jpa_overview_meta_basic" title="2.6. Basic"><code class="classname"> Basic |
| </code></a>. Defaults to <code class="literal">FetchType.EAGER</code>. |
| </p></li><li><p> |
| <code class="literal">CascadeType[] cascade</code>: Array of enum values defining cascade |
| behavior for this field. Corresponds exactly to the same-named property of |
| standard JPA annotations such as <a href="jpa_overview_meta_field.html#jpa_overview_meta_manytoone" title="2.8. Many To One"> |
| <code class="classname"> ManyToOne</code></a>. Defaults to empty array. |
| </p></li><li><p> |
| <code class="literal">String mappedBy</code>: Names the field in the related entity that |
| maps this bidirectional relation. Corresponds to the same-named property of |
| standard JPA annotations such as <a href="jpa_overview_meta_field.html#jpa_overview_meta_onetoone" title="2.10. One To One"> |
| <code class="classname"> OneToOne</code></a>. |
| </p></li><li><p> |
| <code class="literal">boolean optional</code>: Whether the value can be null. Corresponds |
| to the same-named property of standard JPA annotations such as |
| <a href="jpa_overview_meta_field.html#jpa_overview_meta_manytoone" title="2.8. Many To One"><code class="classname"> ManyToOne</code> |
| </a>, but can apply to non-entity object values as well. Defaults to |
| <code class="literal">true</code>. |
| </p></li><li><p> |
| <code class="literal">boolean embedded</code>: Set this property to <code class="literal">true |
| </code> if the field value is stored as an embedded object. |
| </p></li></ul></div><p> |
| Though you can use the <code class="classname">Persistent</code> annotation in place of |
| most of the standard direct field annotations mentioned above, we recommend |
| primarily using it for non-standard and custom types for which no standard JPA |
| annotation exists. For example, <a href="ref_guide_mapping_jpa.html#ref_guide_mapping_jpa_columns" title="7.3. Multi-Column Mappings">Section 7.3, “ |
| Multi-Column Mappings |
| ”</a> |
| demonstrates the use of the <code class="classname">Persistent</code> annotation |
| to denote a persistent <code class="classname">java.awt.Point</code> field. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="ref_guide_meta_jpa_persistent_coll"></a>2.4. Persistent Collection Fields</h3></div></div></div><a class="indexterm" name="d0e24108"></a><p> |
| JPA standardizes support for collections of entities with the <code class="literal"> |
| OneToMany</code> and <code class="literal">ManyToMany</code> persistence strategies. |
| OpenJPA supports these strategies, and may be extended for other strategies as |
| well. For extended strategies, use the |
| <a xmlns:xlink="http://www.w3.org/1999/xlink" href="../javadoc/org/apache/openjpa/persistence/PersistentCollection.html" target="_top"> |
| <code class="classname">org.apache.openjpa.persistence.PersistentCollection</code></a> metadata |
| annotation to represents any persistent collection field. It has the following |
| properties: |
| </p><div class="itemizedlist"><ul type="disc"><li><p> |
| <code class="literal">Class elementType</code>: The class of the collection elements. |
| This information is usually taken from the parameterized collection element |
| type. You must supply it explicitly, however, if your field isn't a |
| parameterized type. |
| </p></li><li><p> |
| <code class="literal">FetchType fetch</code>: Whether to load the collection eagerly or |
| lazily. Corresponds exactly to the same-named property of standard JPA |
| annotations such as <a href="jpa_overview_meta_field.html#jpa_overview_meta_basic" title="2.6. Basic"><code class="classname"> |
| Basic</code></a>. Defaults to <code class="literal">FetchType.LAZY</code>. |
| </p></li><li><p> |
| <code class="literal">String mappedBy</code>: Names the field in the related entity that |
| maps this bidirectional relation. Corresponds to the same-named property of |
| standard JPA annotations such as <a href="jpa_overview_meta_field.html#jpa_overview_meta_manytomany" title="2.11. Many To Many"> |
| <code class="classname">ManyToMany</code></a>. |
| </p></li><li><p> |
| <code class="literal">CascadeType[] elementCascade</code>: Array of enum values defining |
| cascade behavior for the collection elements. Corresponds exactly to the |
| <code class="literal">cascade</code> property of standard JPA annotations such as |
| <a href="jpa_overview_meta_field.html#jpa_overview_meta_manytomany" title="2.11. Many To Many"><code class="classname"> |
| ManyToMany</code></a>. Defaults to empty array. |
| </p></li><li><p> |
| <code class="literal">boolean elementEmbedded</code>: Set this property to <code class="literal">true |
| </code> if the elements are stored as embedded objects. |
| </p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="ref_guide_meta_jpa_persistent_map"></a>2.5. Persistent Map Fields</h3></div></div></div><a class="indexterm" name="d0e24182"></a><p> |
| JPA has limited support for maps. If you extend JPA's standard map support to |
| encompass new mappings, use the |
| <a xmlns:xlink="http://www.w3.org/1999/xlink" href="../javadoc/org/apache/openjpa/persistence/PersistentMap.html" target="_top"> |
| <code class="classname">org.apache.openjpa.persistence.PersistentMap</code></a> metadata |
| annotation to represent your custom persistent map fields. It has the |
| following properties: |
| </p><div class="itemizedlist"><ul type="disc"><li><p> |
| <code class="literal">Class keyType</code>: The class of the map keys. This information |
| is usually taken from the parameterized map key type. You must supply it |
| explicitly, however, if your field isn't a parameterized type. |
| </p></li><li><p> |
| <code class="literal">Class elementType</code>: The class of the map values. This |
| information is usually taken from the parameterized map value type. You must |
| supply it explicitly, however, if your field isn't a parameterized type. |
| </p></li><li><p> |
| <code class="literal">FetchType fetch</code>: Whether to load the collection eagerly or |
| lazily. Corresponds exactly to the same-named property of standard JPA |
| annotations such as <a href="jpa_overview_meta_field.html#jpa_overview_meta_basic" title="2.6. Basic"><code class="classname"> |
| Basic</code></a>. Defaults to <code class="literal">FetchType.LAZY</code>. |
| </p></li><li><p> |
| <code class="literal">CascadeType[] keyCascade</code>: Array of enum values defining |
| cascade behavior for the map keys. Corresponds exactly to the <code class="literal">cascade |
| </code> property of standard JPA annotations such as |
| <a href="jpa_overview_meta_field.html#jpa_overview_meta_manytoone" title="2.8. Many To One"><code class="classname"> |
| ManyToOne</code></a>. Defaults to empty array. |
| </p></li><li><p> |
| <code class="literal">CascadeType[] elementCascade</code>: Array of enum values defining |
| cascade behavior for the map values. Corresponds exactly to the |
| <code class="literal">cascade</code> property of standard JPA annotations such as |
| <a href="jpa_overview_meta_field.html#jpa_overview_meta_manytoone" title="2.8. Many To One"><code class="classname"> |
| ManyToOne</code></a>. Defaults to empty array. |
| </p></li><li><p> |
| <code class="literal">boolean keyEmbedded</code>: Set this property to <code class="literal">true |
| </code> if the map keys are stored as embedded objects. |
| </p></li><li><p> |
| <code class="literal">boolean elementEmbedded</code>: Set this property to <code class="literal"> |
| true</code> if the map values are stored as embedded objects. |
| </p></li></ul></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ref_guide_meta.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ref_guide_meta.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ref_guide_meta_ext.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 6. |
| Metadata |
| </td><td width="20%" align="center"><a accesskey="h" href="manual.html">Home</a></td><td width="40%" align="right" valign="top"> 3. |
| Metadata Extensions |
| </td></tr></table></div></body></html> |