On Aug 2, 2008, at 9:16 PM, Marcin Skladaniec wrote:
Hi
I'm going to add support for horizontal inheritance to cayenne. I've
already added functionality for an entity to be abstract (https://issues.apache.org/cayenne/browse/CAY-794
), now the second part.
BTW, I don't recall those patches being committed. Which patches out
of the 3 files there should go in? Is it just the latest one (abstract-
obj-entity.diff)?
Current implementation of inheritance allows only one of two
parameters set: "inheritance" or "table/view"
If inheritance is selected the ObjEntity does not have any own
DbEntity or DbAttributes, it gets them only from the parent
ObjEntity. (although it has all the ObjAttributes defined in model)
Table/view is a simple approach where the ObjEntity gets its
attributes from its definition in model, there is no parent ObjEntity.
Correct.
For horizontal inheritance ObjEnity.getAttributes() should return
both the attributes defined in model as well as from parent ObjEntity.
Yet having both parameters accepted at the same time might now do it
well enough, therefore I would like to propose adding yet another
parameter to the model: "inheritance db relationship". On database
level the horizontal inheritance is nothing more than a one-to-one
relationship between two tables, and reflecting this in the model
will be required to route the queries and inserts correctly.
Did I miss something ? Is that the right approach ?
Marcin
I think you are talking about VERTICAL inheritance, not horizontal
here. In case of horizontal you wouldn't have a relationship between
subclass/superclass tables. Anyways, assuming we are discussing
vertical inheritance, yes, there is a relationship involved. Per JPA
approach, this relationship can be figured automatically : it is a
1..1 relationship between the PK's of two tables. So we don't have to
store it in XML, as we can find it in runtime. Still internally there
should be a concept of a relationship joining parent and child tables,
so you are right about the big picture.
Andrus
