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https://issues.apache.org/jira/browse/JDO-403?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12507700
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Andy Jefferson commented on JDO-403:
------------------------------------
Why does <field> accept multiple <column> elements ? because it is possible to
map one field to multiple columns in the datastore (ok if you play with
Strings, doubles etc then you dont care about this, but lots of people do).
Taking the same capability with annotations we can specify a field with
@Columns and define multiple columns for it to be persisted into. All I did
with the "columns" property of @Field is apply the same idea for embedded
fields.
An example, using java.awt.Point :-
@EmbeddedOnly
class MyLine
{
Point pt1;
Point pt2;
}
@PersistenceCapable
@Table(name="DRAWINGS")
class MyDrawing
{
@Field
@Embedded(fields={
@Field(embeddedFieldName="pt1",
[EMAIL
PROTECTED](name="PT_1_X"),@Column(name="PT_1_Y")}),
@Field(embeddedFieldName="pt2",
[EMAIL
PROTECTED](name="PT_2_X"),@Column(name="PT_2_Y")})
})
MyLine line;
}
So I have 2 fields in the embedded class, and each of those has 2 columns in
the table of MyDrawing.
CREATE TABLE DRAWINGS
{
...
PT_X_1 INT NULL,
PT_Y_1 INT NULL,
PT_X_2 INT NULL,
PT_Y_2 INT NULL,
...
)
Suppose we could apply the same where the embedded PC has a relation to another
PC and that PC uses a composite PK - hence there are more than 1 column forming
the FK across to it, so we need to be able to specify multiple columns in the
embedded definition
> JDO2 Annotations
> ----------------
>
> Key: JDO-403
> URL: https://issues.apache.org/jira/browse/JDO-403
> Project: JDO
> Issue Type: New Feature
> Components: api2
> Affects Versions: JDO 2 final
> Reporter: Andy Jefferson
> Assignee: Michelle Caisse
> Fix For: JDO 2 maintenance release 1
>
> Attachments: embedded.patch, jdo_2_1_annotations.jar
>
>
> It would be desirable for JDO2 to have its own set of annotations. We have
> developed a set within JPOX that would likely serve as a starting point for
> such a set. In my opinion they should be
> 1. Split into javax.jdo.annotations.jdo and javax.jdo.annotations.orm
> 2. Move ORM attributes from some of the JDO annotations and have a ORM
> annotation.
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