Help Mapping a Composite Foreign Key in JPA 2.0 - orm

Question

I'm new to JPA and I'm trying to map a legacy database. The files load correctly individually but the relationships are not working correctly. Any help would be appreciated.
Java
#Entity
#IdClass(ParentKey.class)
public class Parent {
#Id
#Column(name="code")
private String code;
#Id
#Column(name="id")
private int id;
#OneToMany(mappedBy="parent")
private List<Child> children = new ArrayList<Child>();
}
public class ParentKey {
private String code;
private int id;
}
#Entity
#IdClass(ChildKey.class)
public class Child {
#Id
#JoinColumns({
#JoinColumn(name="code")
#JoinColumn(name="id")
})
private Parent parent;
#Id
#Column(name="index")
private int index;
}
public class ChildKey {
private String code;
private int id;
private int index;
}
SQL
create table Parent(
code char(4) not null,
id int not null,
primary key(code,id)
);
create table Child(
code char(4) not null,
id int not null,
index int not null,
primary key(code, id, index),
foreign key(code, id) references Parent(code,id)
);
edit 1:
add the ChildKey and ParentKey classes.

Answer 1

Here's a link to DataNucleus docs for compound identity 1-N relation. May help you identify what is wrong. For a start you have no IdClass defined on Child
http://www.datanucleus.org/products/accessplatform_3_0/jpa/orm/compound_identity.html#1_N_coll_bi

Answer 2

Here is what OpenJPA created using its ReverseMapping Tool and it appears to be working correctly.
#Entity
#Table(name="PARENT")
#IdClass(ParentId.class)
public class Parent {
#OneToMany(targetEntity=Child.class, mappedBy="parent", cascade=CascadeType.MERGE)
private Set childs = new HashSet();
#Id
#Column(length=4)
private String code;
#Id
private int id;
//omitted getters, setters
}
public class ParentId implements Serializable {
public String code;
public int id;
//omitted getters, setters, toString, equals, hashcode
}
#Entity
#Table(name="CHILD")
#IdClass(ChildId.class)
public class Child {
#Id
#Column(length=4)
private String code;
#Id
private int id;
#Id
private int index;
#ManyToOne(fetch=FetchType.LAZY, cascade=CascadeType.MERGE)
#JoinColumns({#JoinColumn(name="code"), #JoinColumn(name="id")})
private Parent parent;
//omitted getters, setters
}
public class ChildId implements Serializable {
public String code;
public int id;
public int index;
//omitted getters, setters, toString, equals, hashcode
}

Answer 3

See also http://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing#JPA_2.0
(add #Id to #ManyToOne field)