Objectify - save order of Ref<?>-s - google-app-engine

Question

I have a system where I'm trying to minimize the number of Datastore writes (who wouldn't?), all the while using ancestor relations. Consider the following simplified classes:
public class Ancestor {
#Id
private String id;
private String field;
private Ref<Descendant> descendantRef;
public Descendant getDescendant() {
return this.descendantRef.get();
}
public void setDescendant(Descendant des) {
this.descendantRef = Ref.create(des);
}
}
public class Descendant {
#Id
private String id;
private String field;
#Parent
private Key parent;
}
My problem: even though I set the descendant ref, upon saving the Ancestor entity, a null is saved, but if I save the Descendant as well, Objectify complains Attempted to save a null entity.
My question: I gathered that Objectify optimizes the order of get() operations with the #Load annotation, so is there a way to make it do the same on save() operations as well, so that by the time the Ancestor is being sent to the Datastore, the Descendant ref is populated properly?
Thank you in advance for any advice!

Answer 1

You can hide this implementation like this:
public Descendant getDescendant() {
// You probably don't want to break your code on null descendantRef
if (this.descendantRef != null) {
return this.descendantRef.get();
}
return null;
}
public void setDescendant(Descendant des) {
// Insert if this des have never been insert
if (getDescendant() != null) {
new DescendantEndpoint().insert(des);
}
// You probably don't want to break your code on null des
if (des != null) {
this.descendantRef = Ref.create(des);
}
}
By this, you don't have to do deal with each insertion of the ref on each endpoint you will make. Still, this method is not optimized for bulk insert as it will insert on each seperate datastore connection.
For this you can do something like this:
private Object bulkInsertAncestor(ArrayList<Ancestor> list){
ArrayList<Descendant> descendantArrayList = //get descendant list
// You should do all this inside a transaction
new DescendantEndpoint().bulkInsertDescendant(descendantArrayList);
return ofy().save().entities(list);
}

Answer 2

Objectify only complains that you Attempted to save a null entity if you literally pass a null value to the save() method.
This isn't an order-of-operations issue. FWIW, neither Objectify nor the underlying datastore provides any kind of referential integrity checks. It does not matter which you save first.