Remove $facet when an ArrayField is ued as rhs.

Author: WaVEV

django_mongodb_backend/fields/array.py

@@ -310,37 +310,19 @@ class ArrayOverlap(ArrayRHSMixin, FieldGetDbPrepValueMixin, Lookup):
 
     def get_subquery_wrapping_pipeline(self, compiler, connection, field_name, expr):
         return [
+            {"$project": {"tmp_name": expr.as_mql(compiler, connection, as_expr=True)}},
             {
-                "$facet": {
-                    "group": [
-                        {"$project": {"tmp_name": expr.as_mql(compiler, connection, as_expr=True)}},
-                        {
-                            "$unwind": "$tmp_name",
-                        },
-                        {
-                            "$group": {
-                                "_id": None,
-                                "tmp_name": {"$addToSet": "$tmp_name"},
-                            }
-                        },
-                    ]
-                }
+                "$unwind": "$tmp_name",
             },
             {
-                "$project": {
-                    field_name: {
-                        "$ifNull": [
-                            {
-                                "$getField": {
-                                    "input": {"$arrayElemAt": ["$group", 0]},
-                                    "field": "tmp_name",
-                                }
-                            },
-                            [],
-                        ]
-                    }
+                "$group": {
+                    "_id": None,
+                    "tmp_name": {"$addToSet": "$tmp_name"},
                 }
             },
+            {"$unionWith": {"pipeline": [{"$documents": [{"tmp_name": []}]}]}},
+            {"$limit": 1},
+            {"$project": {field_name: "$tmp_name"}},
         ]
 
     def as_mql_expr(self, compiler, connection):

django_mongodb_backend/fields/embedded_model_array.py

@@ -150,44 +150,27 @@ def get_subquery_wrapping_pipeline(self, compiler, connection, field_name, expr)
         # structure of EmbeddedModelArrayField on the RHS behaves similar to
         # ArrayField.
         return [
+            {"$project": {"tmp_name": expr.as_mql(compiler, connection, as_expr=True)}},
+            # To concatenate all the values from the RHS subquery,
+            # use an $unwind followed by a $group.
             {
-                "$facet": {
-                    "gathered_data": [
-                        {"$project": {"tmp_name": expr.as_mql(compiler, connection, as_expr=True)}},
-                        # To concatenate all the values from the RHS subquery,
-                        # use an $unwind followed by a $group.
-                        {
-                            "$unwind": "$tmp_name",
-                        },
-                        # The $group stage collects values into an array using
-                        # $addToSet. The use of {_id: null} results in a
-                        # single grouped array. However, because arrays from
-                        # multiple documents are aggregated, the result is a
-                        # list of lists.
-                        {
-                            "$group": {
-                                "_id": None,
-                                "tmp_name": {"$addToSet": "$tmp_name"},
-                            }
-                        },
-                    ]
-                }
+                "$unwind": "$tmp_name",
             },
+            # The $group stage collects values into an array using
+            # $addToSet. The use of {_id: null} results in a
+            # single grouped array. However, because arrays from
+            # multiple documents are aggregated, the result is a
+            # list of lists.
             {
-                "$project": {
-                    field_name: {
-                        "$ifNull": [
-                            {
-                                "$getField": {
-                                    "input": {"$arrayElemAt": ["$gathered_data", 0]},
-                                    "field": "tmp_name",
-                                }
-                            },
-                            [],
-                        ]
-                    }
+                "$group": {
+                    "_id": None,
+                    "tmp_name": {"$addToSet": "$tmp_name"},
                 }
             },
+            # Add a dummy document in case of empty result.
+            {"$unionWith": {"pipeline": [{"$documents": [{"tmp_name": []}]}]}},
+            {"$limit": 1},
+            {"$project": {field_name: "$tmp_name"}},
         ]
 
 

django_mongodb_backend/lookups.py

@@ -56,34 +56,15 @@ def inner(self, compiler, connection):
 def get_subquery_wrapping_pipeline(self, compiler, connection, field_name, expr):  # noqa: ARG001
     return [
         {
-            "$facet": {
-                "group": [
-                    {
-                        "$group": {
-                            "_id": None,
-                            "tmp_name": {
-                                "$addToSet": expr.as_mql(compiler, connection, as_expr=True)
-                            },
-                        }
-                    }
-                ]
-            }
-        },
-        {
-            "$project": {
-                field_name: {
-                    "$ifNull": [
-                        {
-                            "$getField": {
-                                "input": {"$arrayElemAt": ["$group", 0]},
-                                "field": "tmp_name",
-                            }
-                        },
-                        [],
-                    ]
-                }
+            "$group": {
+                "_id": None,
+                # use a temporal name in order to support field_name="_id"
+                "tmp_name": {"$addToSet": expr.as_mql(compiler, connection, as_expr=True)},
             }
         },
+        {"$unionWith": {"pipeline": [{"$documents": [{"tmp_name": []}]}]}},
+        {"$limit": 1},
+        {"$project": {field_name: "$tmp_name"}},
     ]
 
 

tests/model_fields_/test_arrayfield.py

@@ -634,6 +634,21 @@ def test_overlap_values(self):
             self.objs[:3],
         )
 
+    def test_overlap_empty_values(self):
+        qs = NullableIntegerArrayModel.objects.filter(order__lt=-30)
+        self.assertCountEqual(
+            NullableIntegerArrayModel.objects.filter(
+                field__overlap=qs.values_list("field"),
+            ),
+            [],
+        )
+        self.assertCountEqual(
+            NullableIntegerArrayModel.objects.filter(
+                field__overlap=qs.values("field"),
+            ),
+            [],
+        )
+
     def test_index(self):
         self.assertSequenceEqual(
             NullableIntegerArrayModel.objects.filter(field__0=2), self.objs[1:3]

tests/model_fields_/test_embedded_model_array.py

@@ -520,6 +520,11 @@ def test_subquery_in_lookup(self):
         result = Exhibit.objects.filter(sections__number__in=subquery)
         self.assertCountEqual(result, [self.wonders, self.new_discoveries, self.egypt])
 
+    def test_subquery_empty_in_lookup(self):
+        subquery = Audit.objects.filter(section_number=10).values_list("section_number", flat=True)
+        result = Exhibit.objects.filter(sections__number__in=subquery)
+        self.assertCountEqual(result, [])
+
     def test_array_as_rhs(self):
         result = Exhibit.objects.filter(main_section__number__in=models.F("sections__number"))
         self.assertCountEqual(result, [self.new_discoveries])