Fixed #2445 -- Allowed limit_choices_to attribute to be a callable.

ForeignKey or ManyToManyField attribute ``limit_choices_to`` can now
be a callable that returns either a ``Q`` object or a dict.

Thanks michael at actrix.gen.nz for the original suggestion.

3 files changed, 14 insertions, 8 deletions

diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index e3c3e8e57e..7b0dd8ebcb 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -240,7 +240,7 @@ class BaseModelAdmin(six.with_metaclass(RenameBaseModelAdminMethods)):
         if related_admin is not None:
             ordering = related_admin.get_ordering(request)
             if ordering is not None and ordering != ():
-                return db_field.rel.to._default_manager.using(db).order_by(*ordering).complex_filter(db_field.rel.limit_choices_to)
+                return db_field.rel.to._default_manager.using(db).order_by(*ordering)
         return None
 
     def formfield_for_foreignkey(self, db_field, request=None, **kwargs):
@@ -383,6 +383,9 @@ class BaseModelAdmin(six.with_metaclass(RenameBaseModelAdminMethods)):
         # ForeignKeyRawIdWidget, on the basis of ForeignKey.limit_choices_to,
         # are allowed to work.
         for l in model._meta.related_fkey_lookups:
+            # As ``limit_choices_to`` can be a callable, invoke it here.
+            if callable(l):
+                l = l()
             for k, v in widgets.url_params_from_lookup_dict(l).items():
                 if k == lookup and v == value:
                     return True
diff --git a/django/contrib/admin/utils.py b/django/contrib/admin/utils.py
index 0b74a6e75f..a2f2e9fa7b 100644
--- a/django/contrib/admin/utils.py
+++ b/django/contrib/admin/utils.py
@@ -459,17 +459,17 @@ def get_limit_choices_to_from_path(model, path):
     """ Return Q object for limiting choices if applicable.
 
     If final model in path is linked via a ForeignKey or ManyToManyField which
-    has a `limit_choices_to` attribute, return it as a Q object.
+    has a ``limit_choices_to`` attribute, return it as a Q object.
     """
-
     fields = get_fields_from_path(model, path)
     fields = remove_trailing_data_field(fields)
-    limit_choices_to = (
+    get_limit_choices_to = (
         fields and hasattr(fields[-1], 'rel') and
-        getattr(fields[-1].rel, 'limit_choices_to', None))
-    if not limit_choices_to:
+        getattr(fields[-1].rel, 'get_limit_choices_to', None))
+    if not get_limit_choices_to:
         return models.Q()  # empty Q
-    elif isinstance(limit_choices_to, models.Q):
+    limit_choices_to = get_limit_choices_to()
+    if isinstance(limit_choices_to, models.Q):
         return limit_choices_to  # already a Q
     else:
         return models.Q(**limit_choices_to)  # convert dict to Q
diff --git a/django/contrib/admin/widgets.py b/django/contrib/admin/widgets.py
index f527d72f3f..f501ffb1a8 100644
--- a/django/contrib/admin/widgets.py
+++ b/django/contrib/admin/widgets.py
@@ -180,7 +180,10 @@ class ForeignKeyRawIdWidget(forms.TextInput):
         return mark_safe(''.join(output))
 
     def base_url_parameters(self):
-        return url_params_from_lookup_dict(self.rel.limit_choices_to)
+        limit_choices_to = self.rel.limit_choices_to
+        if callable(limit_choices_to):
+            limit_choices_to = limit_choices_to()
+        return url_params_from_lookup_dict(limit_choices_to)
 
     def url_parameters(self):
         from django.contrib.admin.views.main import TO_FIELD_VAR