On 22/04/2009, at 2:58 AM, Robert Zeigler wrote:
Hm.... have you considered using runtime relationships? (NOTE: I've
never played with this, myself, so take the next bit with a grain of
salt. :)
In theory, it's entirely possible with cayenne to have a single
generic data object and then modify the mapping information at
runtime as necessary.
So... I /think/ you could do something along the following lines:
Register a global lifecycle listener that listens to whatever events
you need: in your case, I would say you probably need post-load and
pre-persist?
And then you can add the relationship information that you need or
that cayenne needs?
Then the info is there for cayenne to work with. And then you can
use the generic writeProperty/writeRelationship methods to access
the information in those properties as needed.
This might be a long shot...dunno... like I said... I haven't tried
it. But if I wanted to have relationships without having
relationships, this is likely the approach I would start looking at.
I'd be interested in hearing what others have to say... feasible
given the current cayenne stack?
Unless you have real database relations you aren't going to get any
benefit of being able to use Cayenne to follow relations. At some
point in Cayenne it will try to follow joins by using SQL JOINs.
Unless Andrus has a trick for making this work, I suspect your
approach is clever but ultimately will run into difficulties.
The problem is that the original poster is trying to use Cayenne like
he uses pure SQL and he hasn't demonstrated how he would even achieve
what he wants with pure SQL (hint: LAST_INSERT_ID() is the mysql
specific way of getting the last id. His other approaches just don't
work. But even LAST_INSERT_ID() would probably create race conditions
with multiple concurrent users.)
There is however a solution to relationships or attributes which need
to be added to 75% of the tables in the database: inheritance. In this
case vertical inheritance is the appropriate choice. We are just now
testing the excellent work Andrus has done in this area and we have
all the basic parts of inheritance working in ROP.
Ari Maniatis
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