Question

I’m having some difficulty to solve this kind of problem:

I Have some nested entities and I’m trying to persist them in the same transaction (HRD enable).

Entity A:

@Entity 
public class A {
    @Id Long id;
    List<B> children;
}

Entity B:

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

When I try to persist 6 instances (just two Entity Groups, A e B) …

public void testOfy() {
    ofy.getFactory().register(A.class);
    ofy.getFactory().register(B.class);

    List<B> list = new ArrayList<B>();

    final A a0 = new A();
    final B b1 = new B();
    final B b2 = new B();
    final B b3 = new B();
    final B b4 = new B();
    final B b5 = new B();

    Ofy o = ofy.transaction();

    try {
        o.save().entities(b1).now(); list.add(b1);
        o.save().entities(b2).now(); list.add(b2);
        o.save().entities(b3).now(); list.add(b3);
        o.save().entities(b4).now(); list.add(b4);
        o.save().entities(b5).now(); list.add(b5);

        a0.children = list;
        o.save(a0);
        o.getTxn().commit();
    }

    finally {
        if (o.getTxn().isActive())
            o.getTxn().rollback();
    }

}

I get the Exception:

java.lang.IllegalArgumentException: operating on too many entity groups in a single transaction.
at com.google.appengine.api.datastore.DatastoreApiHelper.translateError(DatastoreApiHelper.java:36)

However if I put just 5 instances everything works…

public void testOfy() {
    ofy.getFactory().register(A.class);
    ofy.getFactory().register(B.class);

    List<B> list = new ArrayList<B>();

    final A a0 = new A();
    final B b1 = new B();
    final B b2 = new B();
    final B b3 = new B();
    final B b4 = new B();
    final B b5 = new B();

    Ofy o = ofy.transaction();

    try {
        o.save().entities(b1).now(); list.add(b1);
        o.save().entities(b2).now(); list.add(b2);
        o.save().entities(b3).now(); list.add(b3);
        o.save().entities(b4).now(); list.add(b4);
        // o.save().entities(b5).now(); list.add(b5);

        a0.children = list;
        o.save(a0);
        o.getTxn().commit();
    }

    finally {
        if (o.getTxn().isActive())
            o.getTxn().rollback();
    }

}

I’m using Objectify 4.0b3, does anyone have any suggestion?

Thank you!

Answer 1

You have misunderstood what an entity group is. An entity group is not a class, it is an instance (or a group of instances).

Each of those entities represent a separate entity group. XG transactions allow a maximum of five EGs per transaction. The 6th produces the error you see.