Composite key fix when saving indexed keys

Fixing issue where the composited id is not saved correctly into an indexed member set.

This issue is to do with how the adapter writes composite keys into and indexed property set.  The currently implementation only uses the first part of the key - not all of it.

So even though the adapter performs queries in the correct [efficient manner] by looking at the set, it can then never resolve these ids against the hash keys (as they are incorrect) and results in an empty array!