Ok, I've run upon another stumbling block. I did as you recommended and created a Relation model. I'd like to be able to edit/create a Relation inline with a Part in the django admin.
The example provided in the tutorial for editing inline doesn't work in this situation. Is it doable at all? Thanks in advance, Charles On Apr 17, 8:10 pm, "Russell Keith-Magee" <[EMAIL PROTECTED]> wrote: > On 4/18/07, C <[EMAIL PROTECTED]> wrote: > > > > > Hi, > > > I am building a simple parts database as a fun "learn django" project. > > A "part" in my test application has a part number, description, etc > > and can optionally be composed of other parts. This sounded to me > > like a good candidate for a self referring many to many relationship. > > > I got it coded and in the django admin, I can enter part number etc. > > and multi-select from a list of other "part"s. The problem is that if > > I have a part that is composed of say an axle and two wheels (each of > > which are also a part), I don't have a way in the admin to specify > > that there are two wheels. I can only pick one, because only one > > exists. How do I specify that there are two wheels? Is it possible > > to do what I want with the many to many to self model? > > I assume by this that you mean that there is only 1 actual wheel part > in the database, but you want to say that the 'back end of a car' part > contains 1 instance of the axle part and two instances of the wheel > part. > > If this is the case, then no - you don't want a m2m to self. m2m > relations are about saying row X in the database is related to row Y > in the database; you can't add multiple instances of this > relationship. > > What you need is this ability to define the composition, which can > imply multiple instances of a given relationship. There are probably a > number of ways to solve this problem; the 'right' approach will depend > a little bit on your specific requirements. > > One possible solution is to define an m2m relationship with > intermediary data. To do this, you don't put the m2m definition > directly on the Part model - you define a new model that fakes what > the m2m definition does: > > class Relation(Model): > parent = ForeignKey(Part) > child = ForeignKey(Part) > number = IntegerField() > > The instances of relation essentially do what an m2m field does - sets > up a table that connects the two models - but allows you to piggyback > data _about_ the relationship onto each connection. In this case, the > extra data is the number of the child part required to construct the > parent. > > Yours, > Russ Magee %-) --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
