Added support for NULL ON NULL and ABSENT ON NULL on JSONArrayAgg and added necessary tests.

django/db/backends/base/features.py

@@ -339,6 +339,8 @@ class BaseDatabaseFeatures:
 
     # Does the backend support JSONField?
     supports_json_field = True
+    # Does the backend implement support for ABSENT ON NULL clause?
+    supports_json_absent_on_null = True
     # Can the backend introspect a JSONField?
     can_introspect_json_field = True
     # Does the backend support primitives in JSONField?

django/db/backends/mysql/features.py

@@ -60,6 +60,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_virtual_generated_columns = True
 
     supports_json_negative_indexing = False
+    supports_json_absent_on_null = False
 
     @cached_property
     def minimum_database_version(self):

django/db/backends/sqlite3/features.py

@@ -36,6 +36,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_aggregate_distinct_multiple_argument = False
     supports_any_value = True
     order_by_nulls_first = True
+    supports_json_absent_on_null = False
     supports_json_field_contains = False
     supports_update_conflicts = True
     supports_update_conflicts_with_target = True

django/db/models/aggregates.py

@@ -20,6 +20,7 @@ from django.db.models.functions.mixins import (
     FixDurationInputMixin,
     NumericOutputFieldMixin,
 )
+from django.db.models.lookups import IsNull
 
 __all__ = [
     "Aggregate",
@@ -407,11 +408,20 @@ class JSONArrayAgg(Aggregate):
     allow_order_by = True
     arity = 1
 
+    def __init__(self, *expressions, absent_on_null=False, **extra):
+        self.absent_on_null = absent_on_null
+        super().__init__(*expressions, **extra)
+
     def as_sql(self, compiler, connection, **extra_context):
         if self.filter and not connection.features.supports_aggregate_filter_clause:
             raise NotSupportedError(
                 "JSONArrayAgg(filter) is not supported on this database backend."
             )
+        if self.absent_on_null and not connection.features.supports_json_absent_on_null:
+            raise NotSupportedError(
+                "JSONArrayAgg(absent_on_null) is not supported on this database "
+                "backend."
+            )
         return super().as_sql(compiler, connection, **extra_context)
 
     def as_mysql(self, compiler, connection, **extra_context):
@@ -444,21 +454,60 @@ class JSONArrayAgg(Aggregate):
         sql = f"(CASE WHEN {count_sql} > 0 THEN {sql}{default_sql} END)"
         return sql, count_params + params + default_params
 
+    def as_native(self, compiler, connection, *, returning=None, **extra_context):
+        # Oracle and PostgreSQL 16+ default to removing SQL null values from
+        # the returned array. This adds the NULL ON NULL clause to preserve
+        # the null values in the array as default behaviour Similar to that
+        # of SQLite, also removes the null values from the array when
+        # specified via ABSENT ON NULL.
+        if len(self.get_source_expressions()) == 0:
+            on_null_clause = ""
+        elif self.absent_on_null:
+            on_null_clause = "ABSENT ON NULL"
+        else:
+            on_null_clause = "NULL ON NULL"
+        if returning:
+            extra_context.setdefault(
+                "template",
+                "%(function)s(%(distinct)s%(expressions)s%(order_by)s "
+                f"{on_null_clause} RETURNING {returning}) %(filter)s",
+            )
+        else:
+            extra_context.setdefault(
+                "template",
+                "%(function)s(%(distinct)s%(expressions)s%(order_by)s "
+                f"{on_null_clause}) %(filter)s",
+            )
+        return self.as_sql(compiler, connection, **extra_context)
+
     def as_postgresql(self, compiler, connection, **extra_context):
         if not connection.features.is_postgresql_16:
-            sql, params = super().as_sql(
+            sql, params = self.as_sql(
                 compiler,
                 connection,
                 function="ARRAY_AGG",
                 **extra_context,
             )
-            return f"TO_JSONB({sql})", params
-        extra_context.setdefault(
-            "template",
-            "%(function)s(%(distinct)s%(expressions)s%(order_by)s RETURNING JSONB)\
-            %(filter)s",
-        )
-        return self.as_sql(compiler, connection, **extra_context)
+            # Use a filter to cleanly remove null values from the array to
+            # match the behaviour of ABSENT ON NULL on Oracle and
+            # PostgreSQL 16+.
+            if self.absent_on_null:
+                expression = self.get_source_expressions()[0]
+                if self.filter:
+                    not_null_condition = IsNull(expression, False)
+                    copy = self.copy()
+                    copy.filter.source_expressions[0].children += [not_null_condition]
+                    sql, params = copy.as_sql(
+                        compiler, connection, function="ARRAY_AGG", **extra_context
+                    )
+                    return f"TO_JSONB({sql})", params
+                else:
+                    expr, _ = compiler.compile(expression)
+                    filter_sql = f"FILTER (WHERE {expr} IS NOT NULL)"
+                    return f"TO_JSONB({sql} {filter_sql})", params
+            else:
+                return f"TO_JSONB({sql})", params
+        return self.as_native(compiler, connection, returning="JSONB", **extra_context)
 
     def as_oracle(self, compiler, connection, **extra_context):
         # Oracle turns DATE columns into ISO 8601 timestamp including T00:00:00
@@ -474,5 +523,5 @@ class JSONArrayAgg(Aggregate):
                     *source_expressions[1:],
                 ]
             )
-            return clone.as_sql(compiler, connection, **extra_context)
-        return self.as_sql(compiler, connection, **extra_context)
+            return clone.as_native(compiler, connection, **extra_context)
+        return self.as_native(compiler, connection, **extra_context)

tests/aggregation/tests.py

@@ -2737,7 +2737,7 @@ class AggregateAnnotationPruningTests(TestCase):
 class JSONArrayAggTests(TestCase):
     @classmethod
     def setUpTestData(cls):
-        cls.a1 = Author.objects.create(name="Adrian Holovaty", age=34)
+        cls.a1 = Author.objects.create(name="Adrian Holovaty", age=34, rating=1.5)
         cls.a2 = Author.objects.create(name="Jacob Kaplan-Moss", age=45)
         cls.a3 = Author.objects.create(name="Brad Dayley", age=40)
         cls.p1 = Publisher.objects.create(num_awards=3)
@@ -2799,6 +2799,17 @@ class JSONArrayAggTests(TestCase):
         vals = Author.objects.aggregate(jsonarrayagg=JSONArrayAgg("book__pages"))
         self.assertEqual(vals, {"jsonarrayagg": [447, 528, 300]})
 
+    def test_null_on_null(self):
+        vals = Author.objects.aggregate(jsonarrayagg=JSONArrayAgg("rating"))
+        self.assertEqual(vals, {"jsonarrayagg": [1.5, None, None]})
+
+    @skipUnlessDBFeature("supports_json_absent_on_null")
+    def test_absent_on_null(self):
+        vals = Author.objects.aggregate(
+            jsonarrayagg=JSONArrayAgg("rating", absent_on_null=True)
+        )
+        self.assertEqual(vals, {"jsonarrayagg": [1.5]})
+
     @skipUnlessDBFeature("supports_aggregate_filter_clause")
     def test_filter(self):
         vals = Book.objects.aggregate(
@@ -2842,6 +2853,14 @@ class JSONArrayAggTests(TestCase):
         with self.assertRaisesMessage(NotSupportedError, msg):
             Author.objects.aggregate(arrayagg=JSONArrayAgg("age", order_by="-name"))
 
+    @skipIfDBFeature("supports_json_absent_on_null")
+    def test_absent_on_null_not_supported(self):
+        msg = "JSONArrayAgg(absent_on_null) is not supported on this database backend."
+        with self.assertRaisesMessage(NotSupportedError, msg):
+            Author.objects.aggregate(
+                arrayagg=JSONArrayAgg("rating", absent_on_null=True)
+            )
+
     def test_distinct_true(self):
         msg = "JSONArrayAgg does not allow distinct."
         with self.assertRaisesMessage(TypeError, msg):