Thanks All. Thanks Javier. That makes sense, I'm implementing it via a OneToOe relationship now.
On Sep 17, 4:38 am, Tom Evans <tevans...@googlemail.com> wrote: > On Wed, 2009-09-16 at 17:15 -0500, Javier Guerra wrote: > > On Wed, Sep 16, 2009 at 1:01 PM, PlanetUnknown > > <nikhil.kodil...@gmail.com> wrote: > > > > Thanks Karen. > > > Let me explain it a bit more. > > > e.g. > > > All CONTACT details are present in one table - email, home address, > > > work address, home phone, work phone etc. > > > Forget about the statement about growing for now. > > > Since each user "has-a" contact it is a pure one-to-one relationship > > > and not a one-to-many or many-to-one; each user in the USER table will > > > have only one corresponding entry in the CONTACT table. > > > Does this help explaining the issue ? > > > The above is just an example, the main question is how does one > > > usually implement a "has-a" relationship in dJango. > > > i think a big part of your problem is that you're using java-inspired > > OOP terminology. it's much easier if you use RDBMS terminology (after > > all, it will all be stored in a RDBMS). I guess that the Oracle/Java > > systems you're used to show the DB as a persistence system for > > objects, while Django's ORM creates classes that represent the DB. > > same thing, different philosophies. > > > the many-to-one relationship is exactly what you said you used in > > Oracle: a user-id field on the Contact table. > > To me that indicates the wrong relationship. The OP said that all Users > have exactly one Contact. He didn't say that Contacts have users. He > could have a Business model, which could have many contacts etc. > > I would implement this as ForeignKey to Contact on the User model, with > a unique constraint. > > > > > the one-to-one relationship is the same thing, but with an added > > UNIQUE constraint on that key, so that you can have only one contact > > for each user. it has nothing to do with inheritance. the fact that > > inheritance is implemented with one-to-one relationships is just > > incidental. > > > in most cases, you want the possibility of several contacts per user, > > so you can use the many-to-one. the only drawback if that you get an > > extra step to go from user to contact: "User.contact_set.all()". if > > you use one-to-one, the ORM lets you skip that step and write simply > > "User.contact". > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
