Fix #1811: take limit_choices_to into account with FK (#6371)

* Fix issue1811: take limit_choices_to into account with FK

* Issue 1811: Add tests to illustrate issue

* Filter queryset only if limit_choices_to exists

* Move test_relations_with_limited_querysets file within test_relations_pk

* move limit_choices_to logic from relations.py to utils/field_mapping.py

* move limit_choices_to above other check to avoid conflicts

rest_framework/utils/field_mapping.py

@@ -249,6 +249,10 @@ def get_relation_kwargs(field_name, relation_info):
     if to_field:
         kwargs['to_field'] = to_field
 
+    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 has_through_model:
         kwargs['read_only'] = True
         kwargs.pop('queryset', None)

tests/models.py

@@ -52,6 +52,13 @@ class ForeignKeySource(RESTFrameworkModel):
                                on_delete=models.CASCADE)
 
 
+class ForeignKeySourceWithLimitedChoices(RESTFrameworkModel):
+    target = models.ForeignKey(ForeignKeyTarget, help_text='Target',
+                               verbose_name='Target',
+                               limit_choices_to={"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 +5,10 @@
 
 from rest_framework import serializers
 from tests.models import (
-    ForeignKeySource, ForeignKeyTarget, ManyToManySource, ManyToManyTarget,
-    NullableForeignKeySource, NullableOneToOneSource,
-    NullableUUIDForeignKeySource, OneToOnePKSource, OneToOneTarget,
-    UUIDForeignKeyTarget
+    ForeignKeySource, ForeignKeySourceWithLimitedChoices, ForeignKeyTarget,
+    ManyToManySource, ManyToManyTarget, NullableForeignKeySource,
+    NullableOneToOneSource, NullableUUIDForeignKeySource, OneToOnePKSource,
+    OneToOneTarget, UUIDForeignKeyTarget
 )
 
 
@@ -38,6 +38,12 @@ class Meta:
         fields = ('id', 'name', 'target')
 
 
+class ForeignKeySourceWithLimitedChoicesSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = ForeignKeySourceWithLimitedChoices
+        fields = ("id", "target")
+
+
 # Nullable ForeignKey
 class NullableForeignKeySourceSerializer(serializers.ModelSerializer):
     class Meta:
@@ -360,6 +366,18 @@ class Meta(ForeignKeySourceSerializer.Meta):
         serializer.is_valid(raise_exception=True)
         assert 'target' not in serializer.validated_data
 
+    def test_queryset_size_without_limited_choices(self):
+        limited_target = ForeignKeyTarget(name="limited-target")
+        limited_target.save()
+        queryset = ForeignKeySourceSerializer().fields["target"].get_queryset()
+        assert len(queryset) == 3
+
+    def test_queryset_size_with_limited_choices(self):
+        limited_target = ForeignKeyTarget(name="limited-target")
+        limited_target.save()
+        queryset = ForeignKeySourceWithLimitedChoicesSerializer().fields["target"].get_queryset()
+        assert len(queryset) == 1
+
 
 class PKNullableForeignKeyTests(TestCase):
     def setUp(self):