Re: Custom types in PKs and relationships

From analyzing Kanwar's project, I was able to reproduce ClassCastException in an isolated unit test (see
CAY-1728). The cause is essentially the same as FaultFailureException for the same mapping (more on that
below). Whether ClassCastException or FaultFailureException is thrown depends on the order of
internal iteration over properties for a given entity (the relative order of attributes and
relationships in ClassDescriptor.getDeclaredProperties() which is driven by HashMap key hashing
algorithm, i.e. completely obscure to the user). 

But ignore all that for a moment... The cause is that Cayenne is confused by mapping "redundancy" - there's a
meaningful PK that uses custom type , and that same PK is used as a key in a to-many relationship (where
Cayenne can't figure out custom type reliably, and uses default type). 

So what to do about it? We have a long term solution to change type mapping strategy that we are likely to
implement in Cayenne 3.2: http://markmail.org/message/icr7seqazgsdtewc . Until that happens my
advice would be to avoid using custom types for meaningful PKs. E.g. map it as a String and add a pair of extra
methods to convert between String and UUID:

// ignoring possibility of NULLs for a moment...
public UUID getUserMasterUUID() {
  return UUID.fromString(getUserMasterId());
}

public void setUserMasterUUID(UUID uuid) {
   setUserMasterId(uuid.toString());
} 

Not ideal, but should immediately solve your problem. And over time this will get fixed in Cayenne.

Cheers,
Andrus