Yes, "prototype" is a much better word, and such change in
terminology is very important for this discussion to go forward, as
"interface" has a very specific meaning in OO development. Let's
definitely discuss it separately from the inheritance.
Andrus
On May 30, 2007, at 12:32 PM, Aristedes Maniatis wrote:
On 30/05/2007, at 7:16 PM, Andrus Adamchik wrote:
What I am concerned about with DbEntity interfaces is that
DbEntities model database tables and there is no interface concept
in DB world. So I still don't understand why we need DbEntity
inheritance? Could you please elaborate or give some examples?
The only use I can see for it is a *coincidental* match between
groups of attributes in multiple tables. So is it worth
complicating the mapping by introducing a concept with no analog
in the DB world? My suspicion is that it will be very hard to
explain to the users.
Perhaps 'interface' is just the wrong word. The idea is similar to
the WO prototype idea and the most common example is 'money' - you
can define a money type once as having scale=2 and then just use
that in all the dbEntity attributes.
Interfaces in ObjEntities are completely different things again.
They create actual interfaces in the Java classes. Perhaps we
should also shed some of these extra ideas for now and focus on the
main goals:
1. abstract classes
2. horizontal inheritance (where dbEntity=NULL for an objEntity)
3. vertical inheritance (where a special ObjRelationship is created
to specify the superclass. There may also need to be a qualifier
like with single table - Lachlan thinks yes, I'm dubious.)
I believe that is the right order to implement the ideas (easiest
to hardest).
Simultaneously we can work on interfaces. This has two steps:
1. implement interfaces in the modeller, XML, datamap and class
templates but have no runtime code in Cayenne for them. This is
very easy and quite useful on its own.
2. implement the ability for SelectQuery to return a mixture of
objEntities based on a query of the interface
They don't really overlap that much except that some of the issues
faced in making queries work may be applicable to both interfaces
and inheritance.
Finally we have dbEntity interfaces (prototypes) which maybe need
another name and are something different again, but maybe we can
cut them out of this whole conversation and return to them later?
Lachlan, can we drop this one for now?
Ari
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Aristedes Maniatis
phone +61 2 9660 9700
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