Fixed #31046 -- Allowed callable values in through_defaults

Refs django#9475

django/db/models/fields/related_descriptors.py

@@ -68,6 +68,7 @@ class Child(Model):
 from django.db.models import Q, signals
 from django.db.models.query import QuerySet
 from django.db.models.query_utils import DeferredAttribute
+from django.db.models.utils import resolve_callables
 from django.utils.functional import cached_property
 
 
@@ -1118,7 +1119,7 @@ def _add_items(self, source_field_name, target_field_name, *objs, through_defaul
             if not objs:
                 return
 
-            through_defaults = through_defaults or {}
+            through_defaults = dict(resolve_callables(through_defaults or {}))
 
             target_ids = self._get_target_ids(target_field_name, objs)
             db = router.db_for_write(self.through, instance=self.instance)

docs/ref/models/relations.txt

@@ -73,6 +73,14 @@ Related objects reference
         :ref:`intermediate model <intermediary-manytomany>` instance(s), if
         needed.
 
+        .. versionchanged:: 3.1
+
+            You can use callables as values in the ``through_defaults`` dictionary
+            and they will be evaluated before creating any potential
+            intermediate instance(s). Note that the callables are only evaluated
+            once and will therefore have the exact same value for each created
+            intermediate instance.
+
     .. method:: create(through_defaults=None, **kwargs)
 
         Creates a new object, saves it and puts it in the related object set.
@@ -107,6 +115,12 @@ Related objects reference
         :ref:`intermediate model <intermediary-manytomany>` instance, if
         needed.
 
+        .. versionchanged:: 3.1
+
+            You can use callables as values in the ``through_defaults`` dictionary
+            and they will be evaluated just before creating the new
+            intermediate instance.
+
     .. method:: remove(*objs, bulk=True)
 
         Removes the specified model objects from the related object set::
@@ -195,6 +209,14 @@ Related objects reference
         :ref:`intermediate model <intermediary-manytomany>` instance(s), if
         needed.
 
+        .. versionchanged:: 3.1
+
+            You can use callables as values in the ``through_defaults`` dictionary
+            and they will be evaluated before creating any potential
+            intermediate instance(s). Note that the callables are only evaluated
+            once and will therefore have the exact same value for each created
+            intermediate instance.
+
     .. note::
 
        Note that ``add()``, ``create()``, ``remove()``, ``clear()``, and

docs/releases/3.1.txt

@@ -209,6 +209,11 @@ Models
 
 * :attr:`.CheckConstraint.check` now supports boolean expressions.
 
+* Callables can now be used with the ``through_defaults`` argument to
+  :meth:`RelatedManager.add() <django.db.models.fields.related.RelatedManager.add>`,
+  :meth:`~django.db.models.fields.related.RelatedManager.set`, and
+  :meth:`~django.db.models.fields.related.RelatedManager.create`.
+
 Pagination
 ~~~~~~~~~~
 

tests/m2m_through/tests.py

@@ -62,6 +62,11 @@ def test_add_on_m2m_with_intermediate_model(self):
         self.assertSequenceEqual(self.rock.members.all(), [self.bob])
         self.assertEqual(self.rock.membership_set.get().invite_reason, 'He is good.')
 
+    def test_add_on_m2m_with_intermediate_model_callable_through_default(self):
+        self.rock.members.add(self.bob, through_defaults={'invite_reason': lambda: 'He is good.'})
+        self.assertSequenceEqual(self.rock.members.all(), [self.bob])
+        self.assertEqual(self.rock.membership_set.get().invite_reason, 'He is good.')
+
     def test_add_on_m2m_with_intermediate_model_value_required(self):
         self.rock.nodefaultsnonulls.add(self.jim, through_defaults={'nodefaultnonull': 1})
         self.assertEqual(self.rock.testnodefaultsornulls_set.get().nodefaultnonull, 1)