[hibernate-dev] OGM embedded collection handling

[Jonathan Halliday]

So I'm tinkering with the cassandra OGM backend, looking particularly at 
@ElementCollection since cassandra has native collection types, use of 
which would sidestep the current limitations on List's bag semantics at 
the same time as improving performance.

The ORM core we sit on assumes that such collections map to a separate 
table, that being the Relational Way.  So assorted munging of metadata 
is needed to change that model in the backend...

At schema definition time it's necessary to identify which Tables should 
just pass though to underlying db tables and which should be intercepted 
and rewritten as embedded collection types in the owning table. (hint: 
associationKeyMetadata.getAssociationKind() == 
AssociationKind.EMBEDDED_COLLECTION)

Having picked out the ones to embed, it's then necessary to figure out 
what to embed them into. This is where things get sticky - chaining 
through to the EntityKeyMetaData's Table should reveal where the 
collection belongs, but it seems that currently 
OgmCollectionPersister.targetEntityKeyMetadata initialises that to point 
to the embedded table, not the owning entity's table.  IMO that's a bug, 
but I may be misinterpreting the intent of that metadata.  If it is 
behaving correctly, then how can the relationship information be discovered?

thanks

Jonathan.

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