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 <html><head>
       <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
    <title>5.&nbsp; Generators</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 1.2 User's Guide"><link rel="up" href="jpa_overview_mapping.html" title="Chapter&nbsp;12.&nbsp; Mapping Metadata"><link rel="prev" href="jpa_overview_mapping_id.html" title="4.&nbsp; Identity Mapping"><link rel="next" href="jpa_overview_mapping_inher.html" title="6.&nbsp; Inheritance"></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">5.&nbsp;
             Generators
         </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="jpa_overview_mapping_id.html">Prev</a>&nbsp;</td><th width="60%" align="center">Chapter&nbsp;12.&nbsp;
         Mapping Metadata
     </th><td width="20%" align="right">&nbsp;<a accesskey="n" href="jpa_overview_mapping_inher.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="jpa_overview_mapping_sequence"></a>5.&nbsp;
             Generators
         </h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="jpa_overview_mapping_sequence.html#jpa_overview_mapping_sequence_seqgen">5.1.
                 Sequence Generator
             </a></span></dt><dt><span class="section"><a href="jpa_overview_mapping_sequence.html#jpa_overview_mapping_sequence_tablegen">5.2.
                 TableGenerator
             </a></span></dt><dt><span class="section"><a href="jpa_overview_mapping_sequence.html#jpa_overview_mapping_sequence_genex">5.3.
                 Example
             </a></span></dt></dl></div><a class="indexterm" name="d0e9959"></a><a class="indexterm" name="d0e9964"></a><p>
 One aspect of identity mapping not covered in the previous section is JPA's
 ability to automatically assign a value to your numeric identity fields using
 <span class="emphasis"><em>generators</em></span>. We discussed the available generator types in
 <a href="jpa_overview_meta_field.html#jpa_overview_meta_id" title="2.2.&nbsp; Id">Section&nbsp;2.2, &#8220;
                 Id
             &#8221;</a>. Now we show you how to define
 named generators.
         </p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="jpa_overview_mapping_sequence_seqgen"></a>5.1.&nbsp;
                 Sequence Generator
             </h3></div></div></div><a class="indexterm" name="d0e9983"></a><a class="indexterm" name="d0e9988"></a><p>
 Most databases allow you to create native sequences. These are database
 structures that generate increasing numeric values. The <code class="classname">
 SequenceGenerator</code> annotation represents a named database sequence.
 You can place the annotation on any package, entity class, persistent field
 declaration (if your entity uses field access), or getter method for a
 persistent property (if your entity uses property access). <code class="classname">
 SequenceGenerator</code> has the following properties:
             </p><div class="itemizedlist"><ul type="disc"><li><p>
                     <a class="indexterm" name="d0e10003"></a>
 <code class="literal">String name</code>: The generator name. This property is required.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10015"></a>
 <code class="literal">String sequenceName</code>: The name of the database sequence. If
 you do not specify the database sequence, your vendor will choose an appropriate
 default.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10027"></a>
 <code class="literal">int initialValue</code>: The initial sequence value.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10039"></a>
 <code class="literal">int allocationSize</code>: The number of values to allocate in
 memory for each trip to the database. Allocating values in memory allows the JPA
 runtime to avoid accessing the database for every sequence request.
 This number also specifies the amount that the sequence value is incremented
 each time the sequence is accessed. Defaults to 50.
                     </p></li></ul></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
 OpenJPA allows you to use one of OpenJPA's built-in generator
 implementations in the <code class="literal">sequenceName</code> property. You can also
 set the <code class="literal">sequenceName</code> to <code class="literal">system</code> to use the
 system sequence defined by the <a href="ref_guide_conf_openjpa.html#openjpa.Sequence" title="5.59.&nbsp; openjpa.Sequence"><code class="literal">
 openjpa.Sequence</code></a> configuration property. See the Reference
 Guide's <a href="ref_guide_sequence.html" title="6.&nbsp; Generators">Section&nbsp;6, &#8220;
             Generators
         &#8221;</a> for details.
                 </p></div><p>
 The XML element for a sequence generator is <code class="literal">sequence-generator
 </code>. Its attributes mirror the above annotation's properties:
             </p><div class="itemizedlist"><ul type="disc"><li><p>
 <code class="literal">name</code>
                     </p></li><li><p>
 <code class="literal">sequence-name</code>
                     </p></li><li><p>
 <code class="literal">initial-value</code>
                     </p></li><li><p>
 <code class="literal">allocation-size</code>
                     </p></li></ul></div><p>
 To use a sequence generator, set your <code class="classname">GeneratedValue</code>
 annotation's <code class="literal">strategy</code> property to <code class="literal">
 GenerationType.SEQUENCE</code>, and its <code class="literal">generator</code> property
 to the sequence generator's declared name. Or equivalently, set your <code class="literal">
 generated-value</code> XML element's <code class="literal">strategy</code> attribute to
 <code class="literal">SEQUENCE</code> and its <code class="literal">generator</code> attribute to
 the generator name.
             </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="jpa_overview_mapping_sequence_tablegen"></a>5.2.&nbsp;
                 TableGenerator
             </h3></div></div></div><a class="indexterm" name="d0e10125"></a><a class="indexterm" name="d0e10130"></a><p>
 A <code class="classname">TableGenerator</code> refers to a database table used to store
 increasing sequence values for one or more entities. As with <code class="classname">
 SequenceGenerator</code>, you can place the <code class="classname">TableGenerator
 </code> annotation on any package, entity class, persistent field
 declaration (if your entity uses field access), or getter method for a
 persistent property (if your entity uses property access). <code class="classname">
 TableGenerator</code> has the following properties:
             </p><div class="itemizedlist"><ul type="disc"><li><p>
                     <a class="indexterm" name="d0e10151"></a>
 <code class="literal">String name</code>: The generator name. This property is required.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10163"></a>
 <code class="literal">String table</code>: The name of the generator table. If left
 unspecified, your vendor will choose a default table.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10175"></a>
 <code class="literal">String schema</code>: The named table's schema.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10187"></a>
 <code class="literal">String catalog</code>: The named table's catalog.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10199"></a>
 <code class="literal">String pkColumnName</code>: The name of the primary key column in
 the generator table. If unspecified, your implementation will choose a default.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10211"></a>
 <code class="literal">String valueColumnName</code>: The name of the column that holds
 the sequence value. If unspecified, your implementation will choose a default.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10223"></a>
 <code class="literal">String pkColumnValue</code>: The primary key column value of the
 row in the generator table holding this sequence value. You can use the same
 generator table for multiple logical sequences by supplying different <code class="literal">
 pkColumnValue</code> s. If you do not specify a value, the implementation
 will supply a default.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10238"></a>
 <code class="literal">int initialValue</code>: The value of the generator's first issued
 number.
                     </p></li><li><p>
                     <a class="indexterm" name="d0e10250"></a>
 <code class="literal">int allocationSize</code>: The number of values to allocate in
 memory for each trip to the database. Allocating values in memory allows the JPA
 runtime to avoid accessing the database for every sequence request.
 This number also specifies the amount that the sequence value is incremented
 each time the generator table is updated. Defaults to 50.
                     </p></li></ul></div><p>
 The XML equivalent is the <code class="literal">table-generator</code> element. This
 element's attributes correspond exactly to the above annotation's properties:
             </p><div class="itemizedlist"><ul type="disc"><li><p>
 <code class="literal">name</code>
                     </p></li><li><p>
 <code class="literal">table</code>
                     </p></li><li><p>
 <code class="literal">schema</code>
                     </p></li><li><p>
 <code class="literal">catalog</code>
                     </p></li><li><p>
 <code class="literal">pk-column-name</code>
                     </p></li><li><p>
 <code class="literal">value-column-name</code>
                     </p></li><li><p>
 <code class="literal">pk-column-value</code>
                     </p></li><li><p>
 <code class="literal">initial-value</code>
                     </p></li><li><p>
 <code class="literal">allocation-size</code>
                     </p></li></ul></div><p>
 To use a table generator, set your <code class="classname">GeneratedValue</code>
 annotation's <code class="literal">strategy</code> property to <code class="literal">
 GenerationType.TABLE</code>, and its <code class="literal">generator</code> property to
 the table generator's declared name. Or equivalently, set your <code class="literal">
 generated-value</code> XML element's <code class="literal">strategy</code> attribute to
 <code class="literal">TABLE</code> and its <code class="literal">generator</code> attribute to the
 generator name.
             </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="jpa_overview_mapping_sequence_genex"></a>5.3.&nbsp;
                 Example
             </h3></div></div></div><p>
 Let's take advantage of generators in our entity model. Here are our updated
 mappings.
             </p><div class="example"><a name="jpa_overview_mapping_sequenceex"></a><p class="title"><b>Example&nbsp;12.4.&nbsp;
                     Generator Mapping
                 </b></p><div class="example-contents"><pre class="programlisting">
 package org.mag;

 @Entity
 @IdClass(Magazine.MagazineId.class)
 @Table(name="MAG")
 public class Magazine {

     @Column(length=9)
     @Id private String isbn;
     @Id private String title;

     ...

     public static class MagazineId {
         ...
     }
 }

 @Entity
 @Table(name="ART", uniqueConstraints=@Unique(columnNames="TITLE"))
 @SequenceGenerator(name="ArticleSeq", sequenceName="ART_SEQ")
 public class Article {

     @Id
     @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="ArticleSeq")
     private long id;

     ...
 }


 package org.mag.pub;

 @Entity
 @Table(name="COMP")
 public class Company {

     @Column(name="CID")
     @Id private long id;

     ...
 }

 @Entity
 @Table(name="AUTH")
 public class Author {

     @Id
     @GeneratedValue(strategy=GenerationType.TABLE, generator="AuthorGen")
     @TableGenerator(name="AuthorGen", table="AUTH_GEN", pkColumnName="PK",
         valueColumnName="AID")
     @Column(name="AID", columnDefinition="INTEGER64")
     private long id;

     ...
 }

 @Embeddable
 public class Address {
     ...
 }


 package org.mag.subscribe;

 @MappedSuperclass
 public abstract class Document {

     @Id
     @GeneratedValue(generate=GenerationType.IDENTITY)
     private long id;

     ...
 }

 @Entity
 @Table(schema="CNTRCT")
 public class Contract
     extends Document {

     ...
 }

 @Entity
 @Table(name="SUB", schema="CNTRCT")
 public class Subscription {

     @Id
     @GeneratedValue(strategy=GenerationType.IDENTITY)
     private long id;

     ...

     @Entity
     @Table(name="LINE_ITEM", schema="CNTRCT")
     public static class LineItem
         extends Contract {
         ...
     }
 }

 @Entity(name="Lifetime")
 public class LifetimeSubscription
     extends Subscription {
     ...
 }

 @Entity(name="Trial")
 public class TrialSubscription
     extends Subscription {
     ...
 }
 </pre><p>
 The same metadata for <code class="literal">Article</code> and <code class="literal">Author</code>
 expressed in XML form:
                 </p><pre class="programlisting">
 &lt;entity class="org.mag.Article"&gt;
     &lt;table name="ART"&gt;
         &lt;unique-constraint&gt;
             &lt;column-name&gt;TITLE&lt;/column-name&gt;
         &lt;/unique-constraint&gt;
     &lt;/table&gt;
     &lt;sequence-generator name="ArticleSeq" sequence-name="ART_SEQ"/&gt;
     &lt;attributes&gt;
         &lt;id name="id"&gt;
             &lt;generated-value strategy="SEQUENCE" generator="ArticleSeq"/&gt;
         &lt;/id&gt;
         ...
     &lt;/attributes&gt;
 &lt;/entity&gt;
 &lt;entity class="org.mag.pub.Author"&gt;
     &lt;table name="AUTH"/&gt;
     &lt;attributes&gt;
         &lt;id name="id"&gt;
             &lt;column name="AID" column-definition="INTEGER64"/&gt;
             &lt;generated-value strategy="TABLE" generator="AuthorGen"/&gt;
             &lt;table-generator name="AuthorGen" table="AUTH_GEN"
                 pk-column-name="PK" value-column-name="AID"/&gt;
         &lt;/id&gt;
         ...
     &lt;/attributes&gt;
 &lt;/entity&gt;
 </pre></div></div><br class="example-break"></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="jpa_overview_mapping_id.html">Prev</a>&nbsp;</td><td width="20%" align="center"><a accesskey="u" href="jpa_overview_mapping.html">Up</a></td><td width="40%" align="right">&nbsp;<a accesskey="n" href="jpa_overview_mapping_inher.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">4.&nbsp;
             Identity Mapping
         &nbsp;</td><td width="20%" align="center"><a accesskey="h" href="manual.html">Home</a></td><td width="40%" align="right" valign="top">&nbsp;6.&nbsp;
             Inheritance
         </td></tr></table></div></body></html>
	<html><head>
	<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
	<title>5.  Generators</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 1.2 User's Guide"><link rel="up" href="jpa_overview_mapping.html" title="Chapter 12.  Mapping Metadata"><link rel="prev" href="jpa_overview_mapping_id.html" title="4.  Identity Mapping"><link rel="next" href="jpa_overview_mapping_inher.html" title="6.  Inheritance"></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">5.
	Generators
	</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="jpa_overview_mapping_id.html">Prev</a> </td><th width="60%" align="center">Chapter 12.
	Mapping Metadata
	</th><td width="20%" align="right"> <a accesskey="n" href="jpa_overview_mapping_inher.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="jpa_overview_mapping_sequence"></a>5.
	Generators
	</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="jpa_overview_mapping_sequence.html#jpa_overview_mapping_sequence_seqgen">5.1.
	Sequence Generator
	</a></span></dt><dt><span class="section"><a href="jpa_overview_mapping_sequence.html#jpa_overview_mapping_sequence_tablegen">5.2.
	TableGenerator
	</a></span></dt><dt><span class="section"><a href="jpa_overview_mapping_sequence.html#jpa_overview_mapping_sequence_genex">5.3.
	Example
	</a></span></dt></dl></div><a class="indexterm" name="d0e9959"></a><a class="indexterm" name="d0e9964"></a><p>
	One aspect of identity mapping not covered in the previous section is JPA's
	ability to automatically assign a value to your numeric identity fields using
	<span class="emphasis"><em>generators</em></span>. We discussed the available generator types in
	<a href="jpa_overview_meta_field.html#jpa_overview_meta_id" title="2.2.  Id">Section 2.2, “
	Id
	”</a>. Now we show you how to define
	named generators.
	</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="jpa_overview_mapping_sequence_seqgen"></a>5.1.
	Sequence Generator
	</h3></div></div></div><a class="indexterm" name="d0e9983"></a><a class="indexterm" name="d0e9988"></a><p>
	Most databases allow you to create native sequences. These are database
	structures that generate increasing numeric values. The <code class="classname">
	SequenceGenerator</code> annotation represents a named database sequence.
	You can place the annotation on any package, entity class, persistent field
	declaration (if your entity uses field access), or getter method for a
	persistent property (if your entity uses property access). <code class="classname">
	SequenceGenerator</code> has the following properties:
	</p><div class="itemizedlist"><ul type="disc"><li><p>
	<a class="indexterm" name="d0e10003"></a>
	<code class="literal">String name</code>: The generator name. This property is required.
	</p></li><li><p>
	<a class="indexterm" name="d0e10015"></a>
	<code class="literal">String sequenceName</code>: The name of the database sequence. If
	you do not specify the database sequence, your vendor will choose an appropriate
	default.
	</p></li><li><p>
	<a class="indexterm" name="d0e10027"></a>
	<code class="literal">int initialValue</code>: The initial sequence value.
	</p></li><li><p>
	<a class="indexterm" name="d0e10039"></a>
	<code class="literal">int allocationSize</code>: The number of values to allocate in
	memory for each trip to the database. Allocating values in memory allows the JPA
	runtime to avoid accessing the database for every sequence request.
	This number also specifies the amount that the sequence value is incremented
	each time the sequence is accessed. Defaults to 50.
	</p></li></ul></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
	OpenJPA allows you to use one of OpenJPA's built-in generator
	implementations in the <code class="literal">sequenceName</code> property. You can also
	set the <code class="literal">sequenceName</code> to <code class="literal">system</code> to use the
	system sequence defined by the <a href="ref_guide_conf_openjpa.html#openjpa.Sequence" title="5.59.  openjpa.Sequence"><code class="literal">
	openjpa.Sequence</code></a> configuration property. See the Reference
	Guide's <a href="ref_guide_sequence.html" title="6.  Generators">Section 6, “
	Generators
	”</a> for details.
	</p></div><p>
	The XML element for a sequence generator is <code class="literal">sequence-generator
	</code>. Its attributes mirror the above annotation's properties:
	</p><div class="itemizedlist"><ul type="disc"><li><p>
	<code class="literal">name</code>
	</p></li><li><p>
	<code class="literal">sequence-name</code>
	</p></li><li><p>
	<code class="literal">initial-value</code>
	</p></li><li><p>
	<code class="literal">allocation-size</code>
	</p></li></ul></div><p>
	To use a sequence generator, set your <code class="classname">GeneratedValue</code>
	annotation's <code class="literal">strategy</code> property to <code class="literal">
	GenerationType.SEQUENCE</code>, and its <code class="literal">generator</code> property
	to the sequence generator's declared name. Or equivalently, set your <code class="literal">
	generated-value</code> XML element's <code class="literal">strategy</code> attribute to
	<code class="literal">SEQUENCE</code> and its <code class="literal">generator</code> attribute to
	the generator name.
	</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="jpa_overview_mapping_sequence_tablegen"></a>5.2.
	TableGenerator
	</h3></div></div></div><a class="indexterm" name="d0e10125"></a><a class="indexterm" name="d0e10130"></a><p>
	A <code class="classname">TableGenerator</code> refers to a database table used to store
	increasing sequence values for one or more entities. As with <code class="classname">
	SequenceGenerator</code>, you can place the <code class="classname">TableGenerator
	</code> annotation on any package, entity class, persistent field
	declaration (if your entity uses field access), or getter method for a
	persistent property (if your entity uses property access). <code class="classname">
	TableGenerator</code> has the following properties:
	</p><div class="itemizedlist"><ul type="disc"><li><p>
	<a class="indexterm" name="d0e10151"></a>
	<code class="literal">String name</code>: The generator name. This property is required.
	</p></li><li><p>
	<a class="indexterm" name="d0e10163"></a>
	<code class="literal">String table</code>: The name of the generator table. If left
	unspecified, your vendor will choose a default table.
	</p></li><li><p>
	<a class="indexterm" name="d0e10175"></a>
	<code class="literal">String schema</code>: The named table's schema.
	</p></li><li><p>
	<a class="indexterm" name="d0e10187"></a>
	<code class="literal">String catalog</code>: The named table's catalog.
	</p></li><li><p>
	<a class="indexterm" name="d0e10199"></a>
	<code class="literal">String pkColumnName</code>: The name of the primary key column in
	the generator table. If unspecified, your implementation will choose a default.
	</p></li><li><p>
	<a class="indexterm" name="d0e10211"></a>
	<code class="literal">String valueColumnName</code>: The name of the column that holds
	the sequence value. If unspecified, your implementation will choose a default.
	</p></li><li><p>
	<a class="indexterm" name="d0e10223"></a>
	<code class="literal">String pkColumnValue</code>: The primary key column value of the
	row in the generator table holding this sequence value. You can use the same
	generator table for multiple logical sequences by supplying different <code class="literal">
	pkColumnValue</code> s. If you do not specify a value, the implementation
	will supply a default.
	</p></li><li><p>
	<a class="indexterm" name="d0e10238"></a>
	<code class="literal">int initialValue</code>: The value of the generator's first issued
	number.
	</p></li><li><p>
	<a class="indexterm" name="d0e10250"></a>
	<code class="literal">int allocationSize</code>: The number of values to allocate in
	memory for each trip to the database. Allocating values in memory allows the JPA
	runtime to avoid accessing the database for every sequence request.
	This number also specifies the amount that the sequence value is incremented
	each time the generator table is updated. Defaults to 50.
	</p></li></ul></div><p>
	The XML equivalent is the <code class="literal">table-generator</code> element. This
	element's attributes correspond exactly to the above annotation's properties:
	</p><div class="itemizedlist"><ul type="disc"><li><p>
	<code class="literal">name</code>
	</p></li><li><p>
	<code class="literal">table</code>
	</p></li><li><p>
	<code class="literal">schema</code>
	</p></li><li><p>
	<code class="literal">catalog</code>
	</p></li><li><p>
	<code class="literal">pk-column-name</code>
	</p></li><li><p>
	<code class="literal">value-column-name</code>
	</p></li><li><p>
	<code class="literal">pk-column-value</code>
	</p></li><li><p>
	<code class="literal">initial-value</code>
	</p></li><li><p>
	<code class="literal">allocation-size</code>
	</p></li></ul></div><p>
	To use a table generator, set your <code class="classname">GeneratedValue</code>
	annotation's <code class="literal">strategy</code> property to <code class="literal">
	GenerationType.TABLE</code>, and its <code class="literal">generator</code> property to
	the table generator's declared name. Or equivalently, set your <code class="literal">
	generated-value</code> XML element's <code class="literal">strategy</code> attribute to
	<code class="literal">TABLE</code> and its <code class="literal">generator</code> attribute to the
	generator name.
	</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="jpa_overview_mapping_sequence_genex"></a>5.3.
	Example
	</h3></div></div></div><p>
	Let's take advantage of generators in our entity model. Here are our updated
	mappings.
	</p><div class="example"><a name="jpa_overview_mapping_sequenceex"></a><p class="title"><b>Example 12.4.
	Generator Mapping
	</b></p><div class="example-contents"><pre class="programlisting">
	package org.mag;

	@Entity
	@IdClass(Magazine.MagazineId.class)
	@Table(name="MAG")
	public class Magazine {

	@Column(length=9)
	@Id private String isbn;
	@Id private String title;

	...

	public static class MagazineId {
	...
	}
	}

	@Entity
	@Table(name="ART", uniqueConstraints=@Unique(columnNames="TITLE"))
	@SequenceGenerator(name="ArticleSeq", sequenceName="ART_SEQ")
	public class Article {

	@Id
	@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="ArticleSeq")
	private long id;

	...
	}


	package org.mag.pub;

	@Entity
	@Table(name="COMP")
	public class Company {

	@Column(name="CID")
	@Id private long id;

	...
	}

	@Entity
	@Table(name="AUTH")
	public class Author {

	@Id
	@GeneratedValue(strategy=GenerationType.TABLE, generator="AuthorGen")
	@TableGenerator(name="AuthorGen", table="AUTH_GEN", pkColumnName="PK",
	valueColumnName="AID")
	@Column(name="AID", columnDefinition="INTEGER64")
	private long id;

	...
	}

	@Embeddable
	public class Address {
	...
	}


	package org.mag.subscribe;

	@MappedSuperclass
	public abstract class Document {

	@Id
	@GeneratedValue(generate=GenerationType.IDENTITY)
	private long id;

	...
	}

	@Entity
	@Table(schema="CNTRCT")
	public class Contract
	extends Document {

	...
	}

	@Entity
	@Table(name="SUB", schema="CNTRCT")
	public class Subscription {

	@Id
	@GeneratedValue(strategy=GenerationType.IDENTITY)
	private long id;

	...

	@Entity
	@Table(name="LINE_ITEM", schema="CNTRCT")
	public static class LineItem
	extends Contract {
	...
	}
	}

	@Entity(name="Lifetime")
	public class LifetimeSubscription
	extends Subscription {
	...
	}

	@Entity(name="Trial")
	public class TrialSubscription
	extends Subscription {
	...
	}
	</pre><p>
	The same metadata for <code class="literal">Article</code> and <code class="literal">Author</code>
	expressed in XML form:
	</p><pre class="programlisting">
	<entity class="org.mag.Article">
	<table name="ART">
	<unique-constraint>
	<column-name>TITLE</column-name>
	</unique-constraint>
	</table>
	<sequence-generator name="ArticleSeq" sequence-name="ART_SEQ"/>
	<attributes>
	<id name="id">
	<generated-value strategy="SEQUENCE" generator="ArticleSeq"/>
	</id>
	...
	</attributes>
	</entity>
	<entity class="org.mag.pub.Author">
	<table name="AUTH"/>
	<attributes>
	<id name="id">
	<column name="AID" column-definition="INTEGER64"/>
	<generated-value strategy="TABLE" generator="AuthorGen"/>
	<table-generator name="AuthorGen" table="AUTH_GEN"
	pk-column-name="PK" value-column-name="AID"/>
	</id>
	...
	</attributes>
	</entity>
	</pre></div></div><br class="example-break"></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="jpa_overview_mapping_id.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="jpa_overview_mapping.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="jpa_overview_mapping_inher.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">4.
	Identity Mapping
	</td><td width="20%" align="center"><a accesskey="h" href="manual.html">Home</a></td><td width="40%" align="right" valign="top"> 6.
	Inheritance
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