Allowed Q objects in limit_choices_to introspection. (#6472)

Closes #6470.

rest_framework/utils/field_mapping.py

@@ -251,7 +251,9 @@ def get_relation_kwargs(field_name, relation_info):
 
     limit_choices_to = model_field and model_field.get_limit_choices_to()
     if limit_choices_to:
-        kwargs['queryset'] = kwargs['queryset'].filter(**limit_choices_to)
+        if not isinstance(limit_choices_to, models.Q):
+            limit_choices_to = models.Q(**limit_choices_to)
+        kwargs['queryset'] = kwargs['queryset'].filter(limit_choices_to)
 
     if has_through_model:
         kwargs['read_only'] = True

tests/models.py

@@ -59,6 +59,13 @@ class ForeignKeySourceWithLimitedChoices(RESTFrameworkModel):
                                on_delete=models.CASCADE)
 
 
+class ForeignKeySourceWithQLimitedChoices(RESTFrameworkModel):
+    target = models.ForeignKey(ForeignKeyTarget, help_text='Target',
+                               verbose_name='Target',
+                               limit_choices_to=models.Q(name__startswith="limited-"),
+                               on_delete=models.CASCADE)
+
+
 # Nullable ForeignKey
 class NullableForeignKeySource(RESTFrameworkModel):
     name = models.CharField(max_length=100)

tests/test_relations_pk.py

@@ -5,10 +5,11 @@ from django.utils import six
 
 from rest_framework import serializers
 from tests.models import (
-    ForeignKeySource, ForeignKeySourceWithLimitedChoices, ForeignKeyTarget,
-    ManyToManySource, ManyToManyTarget, NullableForeignKeySource,
-    NullableOneToOneSource, NullableUUIDForeignKeySource, OneToOnePKSource,
-    OneToOneTarget, UUIDForeignKeyTarget
+    ForeignKeySource, ForeignKeySourceWithLimitedChoices,
+    ForeignKeySourceWithQLimitedChoices, ForeignKeyTarget, ManyToManySource,
+    ManyToManyTarget, NullableForeignKeySource, NullableOneToOneSource,
+    NullableUUIDForeignKeySource, OneToOnePKSource, OneToOneTarget,
+    UUIDForeignKeyTarget
 )
 
 
@@ -378,6 +379,18 @@ class PKForeignKeyTests(TestCase):
         queryset = ForeignKeySourceWithLimitedChoicesSerializer().fields["target"].get_queryset()
         assert len(queryset) == 1
 
+    def test_queryset_size_with_Q_limited_choices(self):
+        limited_target = ForeignKeyTarget(name="limited-target")
+        limited_target.save()
+
+        class QLimitedChoicesSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = ForeignKeySourceWithQLimitedChoices
+                fields = ("id", "target")
+
+        queryset = QLimitedChoicesSerializer().fields["target"].get_queryset()
+        assert len(queryset) == 1
+
 
 class PKNullableForeignKeyTests(TestCase):
     def setUp(self):