[hibernate-issues] [Hibernate-JIRA] Created: (HHH-4529) Support for derived identity (including @MapsId)

[Emmanuel Bernard (JIRA)]

Support for derived identity (including @MapsId)
------------------------------------------------

                 Key: HHH-4529
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-4529
             Project: Hibernate Core
          Issue Type: Sub-task
          Components: annotations
            Reporter: Emmanuel Bernard
             Fix For: 3.5



2.4.1.1
IdClass (derived side)
"The names of the attributes of the id class and the Id attributes of the dependent entity class 
must correspond as follows: 
• The Id attribute in the entity class and the corresponding attribute in the id class must 
have the same name. 
• If an Id attribute in the entity class is of basic type, the corresponding attribute in the 
id class must have the same type. 
• If an Id attribute in the entity is a many-to-one or one-to-one relationship to a parent 
entity, the corresponding attribute in the id class must be of the same Java type as the 
id class or embedded id of the parent entity (if the parent entity has a composite pri- 
mary key) or the type of the Id attribute of the parent entity (if the parent entity has a 
simple primary key). "

This basically mean that property names int he entity and idClass must match. Types should be identical unless a @Id @XToOne Parent parent; is present in the entity. In this case the corresponding IdClass property should be of the type of the Parent PK

"Alternatively, If the dependent entity has a single primary key attribute (i.e., the relationship attribute), the id 
class specified by the dependent entity must be the same as the primary key class of the parent 
entity. The Id annotation is applied to the relationship to the parent entity."

"If the dependent entity uses an embedded id to represent its primary key, the attribute in the embedded 
id corresponding to the relationship attribute must be of the same type as the primary key of the parent 
entity and must be designated by the MapsId annotation applied to the relationship attribute. The 
value element of the MapsId annotation must be used to specify the name of the attribute within the 
embedded id to which the relationship attribute corresponds.  If the embedded id of the dependent entity 
is of the same Java type as the primary key of the parent entity, the relationship attribute maps both the 
relationship to the parent and the primary key of the dependent entity, and in this case the MapsId 
annotation is specified without the value element."

class Person
  @Id PersonPK id;
  @MapsId("ssnId") @ManyToOne SSN ssn;
  
  static class PersonPK {
  	String name;
  	String ssnId;
  }
}
class SSN {
	@Id String id;
}

"If the dependent entity has a single primary key attribute (i.e, the relationship attribute or an attribute 
that corresponds to the relationship attribute) and the primary key of the parent entity is a simple pri- 
mary key, the primary key of the dependent entity is a simple primary key of the same type as that of the 
parent entity (and neither EmbeddedId nor IdClass is specified).  In this case, either (1) the rela- 
tionship attribute is annotated Id, or (2) a separate Id attribute is specified and the relationship attribute 
is annotated MapsId (and the value element of the MapsId annotation is not specified)"

"A primary key attribute that is derived from the identity of a parent entity is mapped by the correspond- 
ing relationship attribute.  The default mapping for this relationship is as specified in section 2.10.  In 
the case where a default mapping does not apply or where a default mapping is to be overridden, the 
JoinColumn or JoinColumns annotation is used on the relationship attribute. 
If the dependent entity uses an embedded id to represent its primary key, the AttributeOverride 
annotation may be used to override the default mapping of embedded id attributes that do not corre- 
spond to the relationship attributes mapping the derived identity.   The embedded id attributes that cor- 
respond to the relationship are treated by the provider as "read only"—that is, any updates to them on 
the part of the application are not propagated to the database. 
If the dependent uses an id class, the Column annotation may be used to override the default mapping 
of Id attributes that are not relationship attributes. " 


Examples for all that on page 31

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