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

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 fieldclass 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)

After reading through this post and experimenting a lot I think I have found a rather definitive answer to this question. As this is a design pattern that is ofter used I have written a Mixin for the Django admin to make use of it.

(Dynamically) limiting the queryset for ForeignKey fields is now as simple as subclassing LimitedAdminMixin and defining a get_filters(obj) method to return the relevant filters. Alternateively, a filters property can be set on the admin if dynamic filtering is not required.

Example usage:

class MyInline(LimitedAdminInlineMixin, admin.TabularInline):    def get_filters(self, obj):        return (('<field_name>', dict(<filters>)),)

Here, <field_name> is the name of the FK field to be filtered and <filters> is a list of parameters as you would normally specify them in the filter() method of querysets.

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