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?
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