Limit foreign key choices in select in an inline form in admin

Question

The logic is of the model is:

• A Building has many Rooms
• A Room may be inside another Room (a closet, for instance--ForeignKey on 'self')
• A Room can only be inside another Room in the same building (this is the tricky part)

Here's the code I have:

#spaces/models.py from django.db import models      class Building(models.Model):     name=models.CharField(max_length=32)     def __unicode__(self):         return self.name  class Room(models.Model):     number=models.CharField(max_length=8)     building=models.ForeignKey(Building)     inside_room=models.ForeignKey('self',blank=True,null=True)     def __unicode__(self):         return self.number 

and:

#spaces/admin.py from ex.spaces.models import Building, Room from django.contrib import admin  class RoomAdmin(admin.ModelAdmin):     pass  class RoomInline(admin.TabularInline):     model = Room     extra = 2  class BuildingAdmin(admin.ModelAdmin):     inlines=[RoomInline]  admin.site.register(Building, BuildingAdmin) admin.site.register(Room) 

The inline will display only rooms in the current building (which is what I want). The problem, though, is that for the inside_room drop down, it displays all of the rooms in the Rooms table (including those in other buildings).

In the inline of rooms, I need to limit the inside_room choices to only rooms which are in the current building (the building record currently being altered by the main BuildingAdmin form).

I can't figure out a way to do it with either a limit_choices_to in the model, nor can I figure out how exactly to override the admin's inline formset properly (I feel like I should be somehow create a custom inline form, pass the building_id of the main form to the custom inline, then limit the queryset for the field's choices based on that--but I just can't wrap my head around how to do it).

Maybe this is too complex for the admin site, but it seems like something that would be generally useful...

Answer 1

Used request instance as temporary container for obj. Overrided Inline method formfield_for_foreignkey to modify queryset. This works at least on django 1.2.3.

class RoomInline(admin.TabularInline):      model = Room      def formfield_for_foreignkey(self, db_field, request=None, **kwargs):          field = super(RoomInline, self).formfield_for_foreignkey(db_field, request, **kwargs)          if db_field.name == 'inside_room':             if request._obj_ is not None:                 field.queryset = field.queryset.filter(building__exact = request._obj_)               else:                 field.queryset = field.queryset.none()          return field    class BuildingAdmin(admin.ModelAdmin):      inlines = (RoomInline,)      def get_form(self, request, obj=None, **kwargs):         # just save obj reference for future processing in Inline         request._obj_ = obj         return super(BuildingAdmin, self).get_form(request, obj, **kwargs) 

Answer 2

There is limit_choices_to ForeignKey option that allows to limit the available admin choices for the object