Improve virtual relation API

binder/views.py

@@ -1048,7 +1048,7 @@ def _get_with_ids(self, pks, request, include_annotations, with_map, where_map):
 		result = {}
 
 		singular_fields = set()
-		rel_ids_by_field_by_id = defaultdict(lambda: defaultdict(list))
+		rel_ids_by_field_by_id = {}
 		virtual_fields = set()
 
 		for field in with_map:
@@ -1083,7 +1083,7 @@ def _get_with_ids(self, pks, request, include_annotations, with_map, where_map):
 					raise BinderRequestError('Annotation for virtual relation {{{}}}.{{{}}} is {{{}}}, but no method by that name exists.'.format(
 						self.model.__name__, field, virtual_annotation
 					))
-				rel_ids_by_field_by_id[field] = func(request, pks, q)
+				field_rel_ids = func(request, pks, q)
 			# Actual relation
 			else:
 				f = self.model._meta.get_field(field)
@@ -1112,8 +1112,16 @@ def _get_with_ids(self, pks, request, include_annotations, with_map, where_map):
 						.distinct()
 					)
 
+				field_rel_ids = defaultdict(list)
 				for pk, rel_pk in query:
-					rel_ids_by_field_by_id[field][pk].append(rel_pk)
+					field_rel_ids[pk].append(rel_pk)
+
+			# Make sure we always have a result which has exactly the requested
+			# pks as keys
+			rel_ids_by_field_by_id[field] = {
+				pk: list(field_rel_ids.get(pk, []))
+				for pk in pks
+			}
 
 		for field, sub_fields in with_map.items():
 			next = self._follow_related(field)[0].model
@@ -1413,14 +1421,15 @@ def order_by(self, queryset, request):
 
 	def _annotate_obj_with_related_withs(self, obj, field_results):
 		for (w, (view, ids_dict, is_singular)) in field_results.items():
-			if '.' not in w:
-				if is_singular:
-					try:
-						obj[w] = list(ids_dict[obj['id']])[0]
-					except IndexError:
-						obj[w] = None
+			if '.' not in w and obj['id'] in ids_dict:
+				if not is_singular:
+					obj[w] = ids_dict[obj['id']]
+				elif len(ids_dict[obj['id']]) == 0:
+					obj[w] = None
+				elif len(ids_dict[obj['id']]) == 1:
+					obj[w] = ids_dict[obj['id']][0]
 				else:
-					obj[w] = list(ids_dict[obj['id']])
+					raise ValueError(f'multiple values for singular relation {w}: {obj["id"]} -> {ids_dict[obj["id"]]}')
 
 
 	def _generate_meta(self, include_meta, queryset, request, pk=None):

tests/test_virtual_relations.py

@@ -0,0 +1,34 @@
+import json
+
+from django.contrib.auth.models import User
+from django.test import TestCase
+
+from .testapp.models import Zoo, Animal
+
+
+class VirtualRelationTestCase(TestCase):
+
+	def setUp(self):
+		user = User(username='testuser', is_active=True, is_superuser=True)
+		user.set_password('test')
+		user.save()
+
+		self.client.login(username='testuser', password='test')
+
+	def test_virtual_relation(self):
+		pride_rock = Zoo.objects.create(name='Pride Rock')
+		simba = Animal.objects.create(zoo=pride_rock, name='Simba')
+		nala = Animal.objects.create(zoo=pride_rock, name='Nala')
+
+		res = self.client.get(f'/zoo/?with=animals.neighbours&where=animals(id={simba.id})')
+		self.assertEqual(res.status_code, 200)
+		res = json.loads(res.content)
+
+		animals_by_id = {
+			obj['id']: obj
+			for obj in res['with']['animal']
+		}
+
+		self.assertEqual(set(animals_by_id), {simba.id, nala.id})
+		self.assertEqual(animals_by_id[simba.id]['neighbours'], [nala.id])
+		self.assertNotIn('neighbours', animals_by_id[nala.id])

tests/testapp/views/animal.py

@@ -1,3 +1,5 @@
+from django.db.models import F
+
 from binder.views import ModelView
 
 from ..models import Animal
@@ -8,3 +10,22 @@ class AnimalView(ModelView):
 	m2m_fields = ['costume']
 	searches = ['name__icontains']
 	transformed_searches = {'zoo_id': int}
+
+	virtual_relations = {
+		'neighbours': {
+			'model': Animal,
+			'annotation': '_virtual_neighbours',
+			'singular': False,
+		},
+	}
+
+	def _virtual_neighbours(self, request, pks, q):
+		neighbours = {}
+		for pk, neighbour_pk in (
+			Animal.objects
+			.filter(q, zoo__animals__pk__in=pks)
+			.values_list('zoo__animals__pk', 'pk')
+		):
+			if neighbour_pk != pk:
+				neighbours.setdefault(pk, []).append(neighbour_pk)
+		return neighbours