Respect blank on many to many, and set allow_empty=False if it is not present. Closes #2804.

rest_framework/relations.py

@@ -64,6 +64,7 @@ class RelatedField(Field):
             'when setting read_only=`True`.'
         )
         kwargs.pop('many', None)
+        kwargs.pop('allow_empty', None)
         super(RelatedField, self).__init__(**kwargs)
 
     def __new__(cls, *args, **kwargs):

rest_framework/utils/field_mapping.py

@@ -225,6 +225,7 @@ def get_relation_kwargs(field_name, relation_info):
             # If this field is read-only, then return early.
             # No further keyword arguments are valid.
             return kwargs
+
         if model_field.has_default() or model_field.null:
             kwargs['required'] = False
         if model_field.null:
@@ -234,6 +235,8 @@ def get_relation_kwargs(field_name, relation_info):
         if getattr(model_field, 'unique', False):
             validator = UniqueValidator(queryset=model_field.model._default_manager)
             kwargs['validators'] = kwargs.get('validators', []) + [validator]
+        if to_many and not model_field.blank:
+            kwargs['allow_empty'] = False
 
     return kwargs
 

tests/test_model_serializer.py

@@ -395,7 +395,7 @@ class TestRelationalFieldMappings(TestCase):
                 id = IntegerField(label='ID', read_only=True)
                 foreign_key = PrimaryKeyRelatedField(queryset=ForeignKeyTargetModel.objects.all())
                 one_to_one = PrimaryKeyRelatedField(queryset=OneToOneTargetModel.objects.all(), validators=[<UniqueValidator(queryset=RelationalModel.objects.all())>])
-                many_to_many = PrimaryKeyRelatedField(many=True, queryset=ManyToManyTargetModel.objects.all())
+                many_to_many = PrimaryKeyRelatedField(allow_empty=False, many=True, queryset=ManyToManyTargetModel.objects.all())
                 through = PrimaryKeyRelatedField(many=True, read_only=True)
         """)
         self.assertEqual(unicode_repr(TestSerializer()), expected)
@@ -434,7 +434,7 @@ class TestRelationalFieldMappings(TestCase):
                 url = HyperlinkedIdentityField(view_name='relationalmodel-detail')
                 foreign_key = HyperlinkedRelatedField(queryset=ForeignKeyTargetModel.objects.all(), view_name='foreignkeytargetmodel-detail')
                 one_to_one = HyperlinkedRelatedField(queryset=OneToOneTargetModel.objects.all(), validators=[<UniqueValidator(queryset=RelationalModel.objects.all())>], view_name='onetoonetargetmodel-detail')
-                many_to_many = HyperlinkedRelatedField(many=True, queryset=ManyToManyTargetModel.objects.all(), view_name='manytomanytargetmodel-detail')
+                many_to_many = HyperlinkedRelatedField(allow_empty=False, many=True, queryset=ManyToManyTargetModel.objects.all(), view_name='manytomanytargetmodel-detail')
                 through = HyperlinkedRelatedField(many=True, read_only=True, view_name='throughtargetmodel-detail')
         """)
         self.assertEqual(unicode_repr(TestSerializer()), expected)