Fixed #36890 -- Supported StringAgg(distinct=True) on SQLite with the default delimiter.

4 files changed, 41 insertions, 2 deletions

diff --git a/django/db/models/aggregates.py b/django/db/models/aggregates.py
index 1cf82416cb..d1139e8bcc 100644
--- a/django/db/models/aggregates.py
+++ b/django/db/models/aggregates.py
@@ -369,6 +369,24 @@ class StringAgg(Aggregate):
         return sql, (*params, *delimiter_params)
 
     def as_sqlite(self, compiler, connection, **extra_context):
+        if (
+            self.distinct
+            and isinstance(self.delimiter.value, Value)
+            and self.delimiter.value.value == ","
+        ):
+            clone = self.copy()
+            source_expressions = clone.get_source_expressions()
+            clone.set_source_expressions(
+                source_expressions[:1] + source_expressions[2:]
+            )
+
+            return clone.as_sql(
+                compiler,
+                connection,
+                function="GROUP_CONCAT",
+                **extra_context,
+            )
+
         if connection.get_database_version() < (3, 44):
             return self.as_sql(
                 compiler,
diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt
index c819015b25..579c0de302 100644
--- a/docs/ref/models/querysets.txt
+++ b/docs/ref/models/querysets.txt
@@ -4175,7 +4175,14 @@ by the aggregate.
     .. attribute:: delimiter
 
         A ``Value`` or expression representing the string that should separate
-        each of the values. For example, ``Value(",")``.
+        each of the values. For example, ``Value(",")``. (On SQLite, the
+        literal delimiter ``Value(",")`` is the only delimiter compatible with
+        ``distinct=True``.)
+
+        .. versionchanged:: 6.1
+
+            Support for using ``distinct=True`` with a delimiter of
+            ``Value(",")`` on SQLite was added.
 
 Query-related tools
 ===================
diff --git a/docs/releases/6.1.txt b/docs/releases/6.1.txt
index 0d35982543..af783136ad 100644
--- a/docs/releases/6.1.txt
+++ b/docs/releases/6.1.txt
@@ -284,6 +284,9 @@ Models
 * The :data:`~django.db.models.signals.m2m_changed` signal now receives a
   ``raw`` argument.
 
+* :class:`~django.db.models.StringAgg` now supports ``distinct=True`` on SQLite
+  when using the default delimiter ``Value(",")`` only.
+
 Pagination
 ~~~~~~~~~~
 
diff --git a/tests/aggregation/tests.py b/tests/aggregation/tests.py
index bf6bf27031..0a975dcb52 100644
--- a/tests/aggregation/tests.py
+++ b/tests/aggregation/tests.py
@@ -3,6 +3,7 @@ import math
 import re
 from decimal import Decimal
 from itertools import chain
+from unittest import skipUnless
 
 from django.core.exceptions import FieldError
 from django.db import NotSupportedError, connection
@@ -579,6 +580,16 @@ class AggregateTestCase(TestCase):
         )
         self.assertCountEqual(books["ratings"].split(","), ["3", "4", "4.5", "5"])
 
+    @skipUnless(connection.vendor == "sqlite", "Special default case for SQLite.")
+    def test_distinct_on_stringagg_sqlite_special_case(self):
+        """
+        Value(",") is the only delimiter usable on SQLite with distinct=True.
+        """
+        books = Book.objects.aggregate(
+            ratings=StringAgg(Cast(F("rating"), CharField()), Value(","), distinct=True)
+        )
+        self.assertCountEqual(books["ratings"].split(","), ["3.0", "4.0", "4.5", "5.0"])
+
     @skipIfDBFeature("supports_aggregate_distinct_multiple_argument")
     def test_raises_error_on_multiple_argument_distinct(self):
         message = (
@@ -589,7 +600,7 @@ class AggregateTestCase(TestCase):
             Book.objects.aggregate(
                 ratings=StringAgg(
                     Cast(F("rating"), CharField()),
-                    Value(","),
+                    Value(";"),
                     distinct=True,
                 )
             )