There are several approaches (I think in the Hibernate project there are
better explanations from a OO point of view), but I can think of the
following:
1) Association 'dispatcher' table
Ownership
-------------
Row_id
Owner_type
Family_id
Car_id
...
etc
With this approach, as you say, we add columns for every kind of owner
to the Ownership table. It's like a "dispatcher" table, and of course,
if the number of possible owners is very large it drags down (though a
range of 1-15 owner types would be acceptable, IMO)
Or... we could do it backwards:
2) Foreign keys on owner tables
Family
--------
Id
Name
car_id
Company
------------
Id
Name
car_id
Car
----
Id
Name
This doesn't define an "ownership" per se, but allows for lots of owner
types.
The "owners for this car" query gets a little complicated, of course.
There could be other approaches, of course. Weak foreign keys also comes
to mind (a single Owner table with "table" and "id" properties).
--
Ing. Leonardo Quijano Vincenzi
Director Técnico
DTQ Software
Patrick Casey wrote:
How would an association table help me (assuming I wanted to enforce
foreign key integrity there as well)?
Family
------
Id
Name
Company
-------
Id
Name
Cars
-------
Id
Name
Ownership
--------
Row_id
Owned_by (either company or family)
Owner_id
Car_id
Wouldn't owner_id run into the same problem of being a dual FK
relationship? I suppose I could do:
Ownership
--------
Row_id
Family_id (might be null)
Company_id (might be null)
Car_id (fk --> cars(id))
But then as the number of potential car owning tables expands, my
association table gets arbitrarily large, doesn't it?
Or am I missing something obvious here?
--- Pat
---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
