Fixed #33114 -- Defined default output_field of StringAgg.

Thanks Simon Charette for the review.

django/contrib/postgres/aggregates/general.py

@@ -1,7 +1,9 @@
 import warnings
 
 from django.contrib.postgres.fields import ArrayField
-from django.db.models import Aggregate, BooleanField, JSONField, Value
+from django.db.models import (
+    Aggregate, BooleanField, JSONField, TextField, Value,
+)
 from django.utils.deprecation import RemovedInDjango50Warning
 
 from .mixins import OrderableAggMixin
@@ -88,6 +90,7 @@ class StringAgg(DeprecatedConvertValueMixin, OrderableAggMixin, Aggregate):
     function = 'STRING_AGG'
     template = '%(function)s(%(distinct)s%(expressions)s %(ordering)s)'
     allow_distinct = True
+    output_field = TextField()
 
     # RemovedInDjango50Warning
     deprecation_value = ''

tests/postgres_tests/migrations/0002_create_test_models.py

@@ -202,6 +202,7 @@ class Migration(migrations.Migration):
                 ('id', models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True)),
                 ('boolean_field', models.BooleanField(null=True)),
                 ('char_field', models.CharField(max_length=30, blank=True)),
+                ('text_field', models.TextField(blank=True)),
                 ('integer_field', models.IntegerField(null=True)),
                 ('json_field', models.JSONField(null=True)),
             ],

tests/postgres_tests/models.py

@@ -160,6 +160,7 @@ class AggregateTestModel(PostgreSQLModel):
     To test postgres-specific general aggregation functions
     """
     char_field = models.CharField(max_length=30, blank=True)
+    text_field = models.TextField(blank=True)
     integer_field = models.IntegerField(null=True)
     boolean_field = models.BooleanField(null=True)
     json_field = models.JSONField(null=True)

tests/postgres_tests/test_aggregates.py

@@ -25,22 +25,30 @@ class TestGeneralAggregate(PostgreSQLTestCase):
     @classmethod
     def setUpTestData(cls):
         cls.aggs = AggregateTestModel.objects.bulk_create([
-            AggregateTestModel(boolean_field=True, char_field='Foo1', integer_field=0),
+            AggregateTestModel(
+                boolean_field=True,
+                char_field='Foo1',
+                text_field='Text1',
+                integer_field=0,
+            ),
             AggregateTestModel(
                 boolean_field=False,
                 char_field='Foo2',
+                text_field='Text2',
                 integer_field=1,
                 json_field={'lang': 'pl'},
             ),
             AggregateTestModel(
                 boolean_field=False,
                 char_field='Foo4',
+                text_field='Text4',
                 integer_field=2,
                 json_field={'lang': 'en'},
             ),
             AggregateTestModel(
                 boolean_field=True,
                 char_field='Foo3',
+                text_field='Text3',
                 integer_field=0,
                 json_field={'breed': 'collie'},
             ),
@@ -299,6 +307,12 @@ class TestGeneralAggregate(PostgreSQLTestCase):
         values = AggregateTestModel.objects.aggregate(stringagg=StringAgg('char_field', delimiter=';'))
         self.assertEqual(values, {'stringagg': 'Foo1;Foo2;Foo4;Foo3'})
 
+    def test_string_agg_default_output_field(self):
+        values = AggregateTestModel.objects.aggregate(
+            stringagg=StringAgg('text_field', delimiter=';'),
+        )
+        self.assertEqual(values, {'stringagg': 'Text1;Text2;Text4;Text3'})
+
     def test_string_agg_charfield_ordering(self):
         ordering_test_cases = (
             (F('char_field').desc(), 'Foo4;Foo3;Foo2;Foo1'),