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.

AUTHORS

@@ -57,7 +57,7 @@ answer newbie questions, and generally made Django that much better:
 
     Gisle Aas <gisle@aas.no>
     Chris Adams
-    Christopher Adams <christopher.r.adams@gmail.com>
+    Christopher Adams <http://christopheradams.info>
     Mathieu Agopian <mathieu.agopian@gmail.com>
     Roberto Aguilar <roberto@baremetal.io>
     ajs <adi@sieker.info>

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

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

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

django/db/models/fields/__init__.py

@@ -742,11 +742,11 @@ class Field(RegisterLookupMixin):
             lst = [(getattr(x, self.rel.get_related_field().attname),
                    smart_text(x))
                    for x in rel_model._default_manager.complex_filter(
-                       self.rel.limit_choices_to)]
+                       self.get_limit_choices_to())]
         else:
             lst = [(x._get_pk_val(), smart_text(x))
                    for x in rel_model._default_manager.complex_filter(
-                       self.rel.limit_choices_to)]
+                       self.get_limit_choices_to())]
         return first_choice + lst
 
     def get_choices_default(self):

django/db/models/fields/related.py

@@ -309,6 +309,35 @@ class RelatedField(Field):
         if not cls._meta.abstract:
             self.contribute_to_related_class(other, self.related)
 
+    def get_limit_choices_to(self):
+        """Returns 'limit_choices_to' for this model field.
+
+        If it is a callable, it will be invoked and the result will be
+        returned.
+        """
+        if callable(self.rel.limit_choices_to):
+            return self.rel.limit_choices_to()
+        return self.rel.limit_choices_to
+
+    def formfield(self, **kwargs):
+        """Passes ``limit_choices_to`` to field being constructed.
+
+        Only passes it if there is a type that supports related fields.
+        This is a similar strategy used to pass the ``queryset`` to the field
+        being constructed.
+        """
+        defaults = {}
+        if hasattr(self.rel, 'get_related_field'):
+            # If this is a callable, do not invoke it here. Just pass
+            # it in the defaults for when the form class will later be
+            # instantiated.
+            limit_choices_to = self.rel.limit_choices_to
+            defaults.update({
+                'limit_choices_to': limit_choices_to,
+            })
+        defaults.update(kwargs)
+        return super(RelatedField, self).formfield(**defaults)
+
     def related_query_name(self):
         # This method defines the name that can be used to identify this
         # related object in a table-spanning query. It uses the lower-cased
@@ -1525,6 +1554,9 @@ class ForeignObject(RelatedField):
         # and swapped models don't get a related descriptor.
         if not self.rel.is_hidden() and not related.model._meta.swapped:
             setattr(cls, related.get_accessor_name(), self.related_accessor_class(related))
+            # While 'limit_choices_to' might be a callable, simply pass
+            # it along for later - this is too early because it's still
+            # model load time.
             if self.rel.limit_choices_to:
                 cls._meta.related_fkey_lookups.append(self.rel.limit_choices_to)
 
@@ -1633,7 +1665,7 @@ class ForeignKey(ForeignObject):
         qs = self.rel.to._default_manager.using(using).filter(
             **{self.rel.field_name: value}
         )
-        qs = qs.complex_filter(self.rel.limit_choices_to)
+        qs = qs.complex_filter(self.get_limit_choices_to())
         if not qs.exists():
             raise exceptions.ValidationError(
                 self.error_messages['invalid'],
@@ -1691,7 +1723,7 @@ class ForeignKey(ForeignObject):
                              (self.name, self.rel.to))
         defaults = {
             'form_class': forms.ModelChoiceField,
-            'queryset': self.rel.to._default_manager.using(db).complex_filter(self.rel.limit_choices_to),
+            'queryset': self.rel.to._default_manager.using(db),
             'to_field_name': self.rel.field_name,
         }
         defaults.update(kwargs)
@@ -2127,7 +2159,7 @@ class ManyToManyField(RelatedField):
         db = kwargs.pop('using', None)
         defaults = {
             'form_class': forms.ModelMultipleChoiceField,
-            'queryset': self.rel.to._default_manager.using(db).complex_filter(self.rel.limit_choices_to)
+            'queryset': self.rel.to._default_manager.using(db),
         }
         defaults.update(kwargs)
         # If initial is passed in, it's a list of related objects, but the

django/forms/fields.py

@@ -170,6 +170,17 @@ class Field(object):
         """
         return {}
 
+    def get_limit_choices_to(self):
+        """
+        Returns ``limit_choices_to`` for this form field.
+
+        If it is a callable, it will be invoked and the result will be
+        returned.
+        """
+        if callable(self.limit_choices_to):
+            return self.limit_choices_to()
+        return self.limit_choices_to
+
     def _has_changed(self, initial, data):
         """
         Return True if data differs from initial.

django/forms/models.py

@@ -324,6 +324,15 @@ class BaseModelForm(BaseForm):
         self._validate_unique = False
         super(BaseModelForm, self).__init__(data, files, auto_id, prefix, object_data,
                                             error_class, label_suffix, empty_permitted)
+        # Apply ``limit_choices_to`` to each field.
+        for field_name in self.fields:
+            formfield = self.fields[field_name]
+            if hasattr(formfield, 'queryset'):
+                limit_choices_to = formfield.limit_choices_to
+                if limit_choices_to is not None:
+                    if callable(limit_choices_to):
+                        limit_choices_to = limit_choices_to()
+                    formfield.queryset = formfield.queryset.complex_filter(limit_choices_to)
 
     def _get_validation_exclusions(self):
         """
@@ -1082,7 +1091,8 @@ class ModelChoiceField(ChoiceField):
 
     def __init__(self, queryset, empty_label="---------", cache_choices=False,
                  required=True, widget=None, label=None, initial=None,
-                 help_text='', to_field_name=None, *args, **kwargs):
+                 help_text='', to_field_name=None, limit_choices_to=None,
+                 *args, **kwargs):
         if required and (initial is not None):
             self.empty_label = None
         else:
@@ -1094,6 +1104,7 @@ class ModelChoiceField(ChoiceField):
         Field.__init__(self, required, widget, label, initial, help_text,
                        *args, **kwargs)
         self.queryset = queryset
+        self.limit_choices_to = limit_choices_to   # limit the queryset later.
         self.choice_cache = None
         self.to_field_name = to_field_name
 

docs/ref/models/fields.txt

@@ -1078,21 +1078,45 @@ define the details of how the relation works.
 
 .. attribute:: ForeignKey.limit_choices_to
 
-    A dictionary of lookup arguments and values (see :doc:`/topics/db/queries`)
-    that limit the available admin or :class:`ModelForm <django.forms.ModelForm>`
-    choices for this object. For example::
+    Sets a limit to the available choices for this field when this field is
+    rendered using a ``ModelForm`` or the admin (by default, all objects
+    in the queryset are available to choose). Either a dictionary, a
+    :class:`~django.db.models.Q` object, or a callable returning a
+    dictionary or :class:`~django.db.models.Q` object can be used.
+
+    For example::
 
         staff_member = models.ForeignKey(User, limit_choices_to={'is_staff': True})
 
     causes the corresponding field on the ``ModelForm`` to list only ``Users``
-    that have ``is_staff=True``.
+    that have ``is_staff=True``. This may be helpful in the Django admin.
 
-    Instead of a dictionary this can also be a :class:`Q object
-    <django.db.models.Q>` for more :ref:`complex queries
-    <complex-lookups-with-q>`. However, if ``limit_choices_to`` is a :class:`Q
-    object <django.db.models.Q>` then it will only have an effect on the
-    choices available in the admin when the field is not listed in
-    ``raw_id_fields`` in the ``ModelAdmin`` for the model.
+    The callable form can be helpful, for instance, when used in conjunction
+    with the Python ``datetime`` module to limit selections by date range. For
+    example::
+
+        limit_choices_to = lambda: {'pub_date__lte': datetime.date.utcnow()}
+
+    If ``limit_choices_to`` is or returns a :class:`Q object
+    <django.db.models.Q>`, which is useful for :ref:`complex queries
+    <complex-lookups-with-q>`, then it will only have an effect on the choices
+    available in the admin when the field is not listed in
+    :attr:`~django.contrib.admin.ModelAdmin.raw_id_fields` in the
+    ``ModelAdmin`` for the model.
+
+    .. versionchanged:: 1.7
+
+        Previous versions of Django do not allow passing a callable as a value
+        for ``limit_choices_to``.
+
+    .. note::
+
+        If a callable is used for ``limit_choices_to``, it will be invoked
+        every time a new form is instantiated. It may also be invoked when a
+        model is validated, for example by management commands or the admin.
+        The admin constructs querysets to validate its form inputs in various
+        edge cases multiple times, so there is a possibility your callable may
+        be invoked several times.
 
 .. attribute:: ForeignKey.related_name
 

docs/releases/1.7.txt

@@ -608,6 +608,10 @@ Models
 * It is now possible to use ``None`` as a query value for the :lookup:`iexact`
   lookup.
 
+* It is now possible to pass a callable as value for the attribute
+  :attr:`ForeignKey.limit_choices_to` when defining a ``ForeignKey`` or
+  ``ManyToManyField``.
+
 Signals
 ^^^^^^^
 

tests/admin_views/admin.py

@@ -34,7 +34,7 @@ from .models import (Article, Chapter, Child, Parent, Picture, Widget,
     UnchangeableObject, UserMessenger, Simple, Choice, ShortMessage, Telegram,
     FilteredManager, EmptyModelHidden, EmptyModelVisible, EmptyModelMixin,
     State, City, Restaurant, Worker, ParentWithDependentChildren,
-    DependentChild)
+    DependentChild, StumpJoke)
 
 
 def callable_year(dt_value):
@@ -884,6 +884,7 @@ site.register(ParentWithDependentChildren, ParentWithDependentChildrenAdmin)
 site.register(EmptyModelHidden, EmptyModelHiddenAdmin)
 site.register(EmptyModelVisible, EmptyModelVisibleAdmin)
 site.register(EmptyModelMixin, EmptyModelMixinAdmin)
+site.register(StumpJoke)
 
 # Register core models we need in our tests
 from django.contrib.auth.models import User, Group

tests/admin_views/models.py

@@ -173,6 +173,33 @@ class Sketch(models.Model):
         return self.title
 
 
+def today_callable_dict():
+    return {"last_action__gte": datetime.datetime.today()}
+
+
+def today_callable_q():
+    return models.Q(last_action__gte=datetime.datetime.today())
+
+
+@python_2_unicode_compatible
+class Character(models.Model):
+    username = models.CharField(max_length=100)
+    last_action = models.DateTimeField()
+
+    def __str__(self):
+        return self.username
+
+
+@python_2_unicode_compatible
+class StumpJoke(models.Model):
+    variation = models.CharField(max_length=100)
+    most_recently_fooled = models.ForeignKey(Character, limit_choices_to=today_callable_dict, related_name="+")
+    has_fooled_today = models.ManyToManyField(Character, limit_choices_to=today_callable_q, related_name="+")
+
+    def __str__(self):
+        return self.variation
+
+
 class Fabric(models.Model):
     NG_CHOICES = (
         ('Textured', (

tests/admin_views/tests.py

@@ -52,7 +52,7 @@ from .models import (Article, BarAccount, CustomArticle, EmptyModel, FooAccount,
     Report, MainPrepopulated, RelatedPrepopulated, UnorderedObject,
     Simple, UndeletableObject, UnchangeableObject, Choice, ShortMessage,
     Telegram, Pizza, Topping, FilteredManager, City, Restaurant, Worker,
-    ParentWithDependentChildren)
+    ParentWithDependentChildren, Character)
 from .admin import site, site2, CityAdmin
 
 
@@ -3661,6 +3661,33 @@ class ReadonlyTest(TestCase):
         self.assertEqual(response.status_code, 200)
 
 
+@override_settings(PASSWORD_HASHERS=('django.contrib.auth.hashers.SHA1PasswordHasher',))
+class LimitChoicesToInAdminTest(TestCase):
+    urls = "admin_views.urls"
+    fixtures = ['admin-views-users.xml']
+
+    def setUp(self):
+        self.client.login(username='super', password='secret')
+
+    def tearDown(self):
+        self.client.logout()
+
+    def test_limit_choices_to_as_callable(self):
+        """Test for ticket 2445 changes to admin."""
+        threepwood = Character.objects.create(
+            username='threepwood',
+            last_action=datetime.datetime.today() + datetime.timedelta(days=1),
+        )
+        marley = Character.objects.create(
+            username='marley',
+            last_action=datetime.datetime.today() - datetime.timedelta(days=1),
+        )
+        response = self.client.get('/test_admin/admin/admin_views/stumpjoke/add/')
+        # The allowed option should appear twice; the limited option should not appear.
+        self.assertContains(response, threepwood.username, count=2)
+        self.assertNotContains(response, marley.username)
+
+
 @override_settings(PASSWORD_HASHERS=('django.contrib.auth.hashers.SHA1PasswordHasher',))
 class RawIdFieldsTest(TestCase):
     urls = "admin_views.urls"

tests/model_forms/models.py

@@ -8,6 +8,7 @@ words, most of these tests should be rewritten.
 """
 from __future__ import unicode_literals
 
+import datetime
 import os
 import tempfile
 
@@ -71,7 +72,6 @@ class Article(models.Model):
     status = models.PositiveIntegerField(choices=ARTICLE_STATUS, blank=True, null=True)
 
     def save(self):
-        import datetime
         if not self.id:
             self.created = datetime.date.today()
         return super(Article, self).save()
@@ -329,3 +329,21 @@ class CustomErrorMessage(models.Model):
     def clean(self):
         if self.name1 == 'FORBIDDEN_VALUE':
             raise ValidationError({'name1': [ValidationError('Model.clean() error messages.')]})
+
+
+def today_callable_dict():
+    return {"last_action__gte": datetime.datetime.today()}
+
+
+def today_callable_q():
+    return models.Q(last_action__gte=datetime.datetime.today())
+
+
+class Character(models.Model):
+    username = models.CharField(max_length=100)
+    last_action = models.DateTimeField()
+
+
+class StumpJoke(models.Model):
+    most_recently_fooled = models.ForeignKey(Character, limit_choices_to=today_callable_dict, related_name="+")
+    has_fooled_today = models.ManyToManyField(Character, limit_choices_to=today_callable_q, related_name="+")

tests/model_forms/tests.py

@@ -22,7 +22,8 @@ from .models import (Article, ArticleStatus, BetterWriter, BigInt, Book,
     DerivedPost, ExplicitPK, FlexibleDatePost, ImprovedArticle,
     ImprovedArticleWithParentLink, Inventory, Post, Price,
     Product, TextFile, Writer, WriterProfile, Colour, ColourfulItem,
-    ArticleStatusNote, DateTimePost, CustomErrorMessage, test_images)
+    ArticleStatusNote, DateTimePost, CustomErrorMessage, test_images,
+    StumpJoke, Character)
 
 if test_images:
     from .models import ImageFile, OptionalImageFile
@@ -521,6 +522,12 @@ class FieldOverridesTroughFormMetaForm(forms.ModelForm):
         }
 
 
+class StumpJokeForm(forms.ModelForm):
+    class Meta:
+        model = StumpJoke
+        fields = '__all__'
+
+
 class TestFieldOverridesTroughFormMeta(TestCase):
     def test_widget_overrides(self):
         form = FieldOverridesTroughFormMetaForm()
@@ -1921,3 +1928,34 @@ class ModelFormInheritanceTests(TestCase):
         self.assertEqual(list(type(str('NewForm'), (ModelForm, Mixin, Form), {})().fields.keys()), ['name'])
         self.assertEqual(list(type(str('NewForm'), (ModelForm, Form, Mixin), {})().fields.keys()), ['name', 'age'])
         self.assertEqual(list(type(str('NewForm'), (ModelForm, Form), {'age': None})().fields.keys()), ['name'])
+
+
+class LimitChoicesToTest(TestCase):
+    """
+    Tests the functionality of ``limit_choices_to``.
+    """
+    def setUp(self):
+        self.threepwood = Character.objects.create(
+            username='threepwood',
+            last_action=datetime.datetime.today() + datetime.timedelta(days=1),
+        )
+        self.marley = Character.objects.create(
+            username='marley',
+            last_action=datetime.datetime.today() - datetime.timedelta(days=1),
+        )
+
+    def test_limit_choices_to_callable_for_fk_rel(self):
+        """
+        A ForeignKey relation can use ``limit_choices_to`` as a callable, re #2554.
+        """
+        stumpjokeform = StumpJokeForm()
+        self.assertIn(self.threepwood, stumpjokeform.fields['most_recently_fooled'].queryset)
+        self.assertNotIn(self.marley, stumpjokeform.fields['most_recently_fooled'].queryset)
+
+    def test_limit_choices_to_callable_for_m2m_rel(self):
+        """
+        A ManyToMany relation can use ``limit_choices_to`` as a callable, re #2554.
+        """
+        stumpjokeform = StumpJokeForm()
+        self.assertIn(self.threepwood, stumpjokeform.fields['has_fooled_today'].queryset)
+        self.assertNotIn(self.marley, stumpjokeform.fields['has_fooled_today'].queryset)