James, one thing you might consider is creating an M2M relation between edges and nodes. That won't allow you to enforce at a database level the rule that edges relate to exactly one or two nodes, but it will work pretty naturally at the model level -- each node has a set of related edges, and each edge has a set of related nodes.
-- Scott On Wed, May 14, 2008 at 3:43 AM, James Tauber <[EMAIL PROTECTED]> wrote: > > On a couple of occasions, I've had need for a model that links two > instances of another model and I'm wondering about the best practices > for doing this. > > Abstractly, there's an undirected graph where both nodes and arcs are > objects. > > Concretely, two examples are: > > 1) roads in django-mmo existing between two hubs but the roads aren't > directed: A to B means the same as B to A > > 2) friendship in django-friends existing between two users where > friendship is necessarily mutual: a Friends b => b Friends a > > Obviously this can be done with Road or Friendship having two foreign > keys but (a) this leads to a superfluous related_name; (b) how do you > best query a node for its arcs? > > If the arc were just a M2M field on the node, one could use > symmetrical=True but it isn't clear to me the best way to do this > where the arc/association is its own model. > > James > -- > James Tauber http://jtauber.com/ > journeyman of some http://jtauber.com/blog/ > > > > > > > > -- http://scott.andstuff.org/ | http://truthadorned.org/ --~--~---------~--~----~------------~-------~--~----~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
