Re: [eclipselink-users] Question about Embeddable Classes

["Guy Pelletier" <guy.pelletier@xxxxxxxxxx>]

Daniel,

N levels of embeddable can be supported.

Yes, your recursive model is causing the stack overflow, you can't do that.

Collection's of embeddable will soon be supported through the use of 
ElementCollection from JPA2. In the mean time yes, you may use a descriptor 
customizer to map this manually. See @Customizer for more details. Your 
customizer class must implement the 
org.eclipse.persistence.config.DescriptorCustomizer interface.

Cheers,
Guy

----- Original Message ----- 
From: <Daniel.Stucky@xxxxxxxxxxx>
To: <eclipselink-users@xxxxxxxxxxx>
Sent: Tuesday, January 27, 2009 8:24 AM
Subject: [eclipselink-users] Question about Embeddable Classes


Hi,

the JPA 1.0 specification says about embeddable classes
- "Support for only one level of embedding is required by this
specification."
- "Support for collections of embedded objects and for the polymorphism
and inheritance of embeddable classes will be required in
a future release of this specification."

I did a test with the following classes that worked fine:

@Entity
public class MyRecordImpl{

 @Id
 @Column(name = "ID")
 private String _id;

 @Embedded
 private MyAttributeImpl _attribute;
}

@Embeddable
public class MyAttributeImpl{

 @Column(name = "ATT_NAME")
 private String _name;

 @Column(name = "ATT_VALUE")
 private String _value;

 @Embedded
 @Column(name = "ANNOTATION")
 private MyAnnotationImpl _annaotation;
}

@Embeddable
public class MyAnnotationImpl{

 @Column(name = "ANON_NAME")
 private String _name;

 @Column(name = "ANON_VALUE")
 private String _value;
}

Does eclipseLink support more than one level of embedding or did this
just function by accident ?
How many levels are supported ?


Would it be possible to recursively embed objects, like

@Entity
public class MyRecordImpl{

 @Id
 @Column(name = "ID")
 private String _id;

 @Embedded
 private MyAttributeImpl _attribute;
}

@Embeddable
public class MyAttributeImpl{

 @Column(name = "ATT_NAME")
 private String _name;

 @Column(name = "ATT_VALUE")
 private String _value;

 @Embedded
 @Column(name = "REF_ATTRIBUTE")
 private MyAttributeImpl _attribute;
}

When I try this I get a java.lang.StackOverflowError, presumably because
of the recursion.


Also I've read that eclipseLink supports collections of embeddable and
that it is set through using a DescriptorCustomizer and the
AggregateCollectionMapping. Are there any examples in the wiki ? I found
some documentation that I was unable to understand.
I guess something like  private List<MyAttributeImpl> _attributes; as a
member of MyAttributeImpl would still not be supported.


Bye,
Daniel

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