I have my java classes as

Class Parent{

@ID
@GeneratedValue(strategy=GenerationType.Identity)
@Column(id)
Int id;

@oneToOne(mapped by=parent, Cascade=CascadeType.All)
Child1 c1;

@oneToOne(mapped by=parent,Cascade=CascadeType.All)
Child2 c2;

// getter setter

}


Class Child1{

@ID
@GeneratedValue(generator = "gen")
@GenericGenerator(name="gen", strategy="foreign", parameters=@Parameter(name="property", value="parent"))
@Column(id)
Int id;

@oneToOne
@primaryKeyJoinColumn
Parent parent;

@oneToMany(mapped by=child1,Cascade=CascadeType.All)
List<Toy> toys;

// getter setter

}


Class Child2{

@ID
@GeneratedValue(generator = "gen")
@GenericGenerator(name="gen", strategy="foreign", parameters=@Parameter(name="property", value="parent"))
@Column(id)
Int id;

@oneToOne
@primaryKeyJoinColumn
Parent parent;

@oneToMany(mapped by=child2,Cascade=CascadeType.All)
List<Toy> toys;

// getter setter

}

Class Toy{

@EmbeddedId
ToyPk toyid;

@manytoOne
@joinColumn(name="id1")
@MapsId("id1")
Child1 child1;

@manytoOne
@joinColumn(name="id1")
@MapsId("id1")
Child2 child2

// getter setter
}

@Embeddable
Class ToyPk{

@column("id1")
int id1;

@column("id2")
int id2;

//getter setter
}

At time of save or retrieve, i can have either Parent-Child1-Toy list or Parent-Child2-Toy list. When i save object with Parent-Child1-Toy list, i get exception= "attempted to assign id from null one to one(TOY.child2)".
What should i do?