Objectify - How to declare a foreign key?

Question

I am working with Google app engine and Objectify. I am unable to find that how to declare foreign key in Objectify.

Any help would be really appreciated.

Thanks.

Answer 1

Google App Engine datastore is not an RDBMS database, so the concept of the Foreign Key doesn't specifically exist. You can save a reference from an entity A to an entity B by having a Key property in A of B. For example consider the following:

@Entity
public class A {
    @Id Long id;
}

@Entity
public class B {
    @Id Long id;
    Key<A> referenceToA;
}

For more information about data modeling in GAE, take a look at:

• Entity Relationships in JDO
• Modeling Entity Relationships

Hope this helps!