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update document on derived identity 

git-svn-id: https://svn.apache.org/repos/asf/openjpa/trunk@814937 13f79535-47bb-0310-9956-ffa450edef68
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Fay Wang 2009-09-14 23:39:02 +00:00
parent 492a19573c
commit bda0136758
1 changed files with 66 additions and 6 deletions
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72
openjpa-project/src/doc/manual/ref_guide_pc.xml
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@ -686,8 +686,7 @@ record.
</tertiary>
</indexterm>
<para>
The JPA specification limits identity fields to simple types. OpenJPA, however,
also allows <literal>ManyToOne</literal> and <literal>OneToOne</literal>
OpenJPA allows <literal>ManyToOne</literal> and <literal>OneToOne</literal>
relations to be identity fields. To identify a relation field as an identity
field, simply annotate it with both the <literal>@ManyToOne</literal> or
<literal>@OneToOne</literal> relation annotation and the <literal>@Id</literal>
@ -718,12 +717,17 @@ public Delivery findDelivery(EntityManager em, Order order) {
</example>
<para>
When your entity has multiple identity fields, at least one of which is a
relation to another entity, you must use an identity class (see
<xref linkend="jpa_overview_pc_identitycls"/> in the JPA Overview). You cannot
use an embedded identity object. Identity class fields corresponding to
relation to another entity, you can use an identity class (see
<xref linkend="jpa_overview_pc_identitycls"/> in the JPA Overview), or
an embedded identity object. Identity class fields corresponding to
entity identity fields should be of the same type as the related entity's
identity.
identity. If an embedded identity object is used, you must annotate the
relation field with both the <literal>@ManyToOne</literal> or
<literal>@OneToOne</literal> relation annotation and the
<literal>@MappedById</literal> annotation.
</para>
<example id="ref_guide_pc_oid_entitypk_idcls">
<title>
Id Class for Entity Identity Fields
@ -771,7 +775,63 @@ class <classname>OrderId</classname> in place of a simple <classname>long
</classname> value, then the <literal>LineItemId.order</literal> field would
have been of type <classname>OrderId</classname>.
</para>
<example id="ref_guide_pc_oid_entitypk_embeded_id">
<title>
Embedded Id for Entity Identity Fields
</title>
<programlisting>
@Entity
public class Order {
@Id
private long id;
...
}
/**
* LineItem uses a compound primary key. Part of the compound key
* LineItemId is relation or reference to Order instance.
**/
@Entity
public class LineItem {
@EmbeddedId LineItemId id;
@ManyToOne
@MappedById("orderId") // The value element of the MappedById annotation
// must be used to specify the name of the primary
// key attribute to which the relationship
// corresponds. If the primary key referenced by
// the relationship attribute is of the same Java
// type as the dependent's primary key, then the
// value element is not specified.
private Order order;
...
}
@Embeddable
public class LineItemId {
public int index;
public long orderId;
}
</programlisting>
</example>
<para>
In the example above, the <classname>LineItem</classname> uses an embedded id to
represent its primary key. The primary key attribute corresponding to the
relationship in the <classname>LineItemId</classname> must be of the same
type as the primary key of the <classname>Order</classname>. The
<literal>MappedById</literal> annotation must be applied to the relationship
field <literal>LineItem.order</literal>.
</para>
</section>
<section id="ref_guide_pc_oid_application">
<title>
Application Identity Tool