stableIdForObject
Use stableIdForObject to provide FakeResolverContext.id. You can then use FakeResolverContext.id to derive stable values in the resolveXyz() methods above. This way, you're guaranteed that a fake object will have the same field values no matter its path in the query.
Return
a cache key for the given field
Parameters
obj
the representation of the object. It contains all user defined values. If you do not provide a value, this method is not called.