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Joe M
Joe M

Reputation: 2657

How to explicitly specify the 'inverse' @OneToMany relationship in JPA

I am using JPA discriminators to obtain specific sub classes as follows (class names changed for simplicity)

@Entity
@Table(name="TYPE")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="SUB_TYPE", discriminatorType=DiscriminatorType.INTEGER)
public class Type {
   @ManyToOne(fetch=FetchType.LAZY)
   @JoinColumn(name="TID")
   private Foo foo; 
}

@Entity
@DiscriminatorValue("1")
public class Type1 extends Type {
    //Type1 stuff
}

//Other Type subclasses

As you can see "Type" class is in a many-to-one relationship with the Foo class, however in generics as Set<Type1> is not a subtype of Set<Type> we cannot just speicify the 'inverse' relationship in Foo as Set<Type> types;

Therefore my Foo class uses wildcards but also ensures that only subclasses of Type can be set as types as follows;

@Entity
@Table(name="FOO")
public class Foo {

    //bi-directional one-to-many association to Type
    @OneToMany(mappedBy="foo")
    Set<?> types;

    public Set<?> getTypes() {
            return types;
    }

    public void setTypes(Set<? extends Type> types) {
            this.types = types;
    }   
}

The question is - how do I explicitly tell JPA that the Set should be of type 'Type'? If this is not possible, what are my alternatives to setting this inverse relationship, while still using discriminators?

Upvotes: 1

Views: 388

Answers (1)

Chris
Chris

Reputation: 21145

The OneToMany annotation can specify the targetEntity:

  @OneToMany(mappedBy="foo", targetEntity = Type.class)
  Set<?> types;

This is optional when generics can be used to define the type, but required in your situation.

http://docs.oracle.com/javaee/6/api/javax/persistence/OneToMany.html

Upvotes: 1

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