In our Cayenne ROP application we have some tables with very large BLOB fields.
We want to be able to fetch the remaining columns to the client, without the
BLOBs. I am after some ideas on how to best approach this:
1. Create two tables and two Cayenne Java entities to match
Cons: makes the code and database messy since we are dealing with one-to-one
relationships where there isn't really any logical relation
2. Create one database table and use single-table inheritance: the superclass
(say 'Painting') has all the fields and the subclass ('PaintingInfo') only the
lightweight fields
Cons: the code is still messy since casting a PaintingInfo to Painting (should
you want to view the BLOB) isn't really possible. You would have to get the PK
and then perform another full fetch on the parent. And I'd be concerned about
having two objects in memory at the same time which point to the same data, but
aren't synchronised to each other.
3. Devise some mechanism for Cayenne to have not just hollow objects (like what
happens with paged queries) but hollow attributes. Then we only lazily fetch
the attribute data when it is needed (if at all). This could be ROP specific
(that is, the BLOB attributes are fully fetched from the database but not sent
to the client until needed) or perhaps this approach would also be useful in a
non-ROP environment for lazily loading columns.
Any thoughts from people who have run into similar issues? I'd like to avoid
DataRows and all that since that just makes the code really messy again.
Ari
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Aristedes Maniatis
ish
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