Refs #34058 -- Fixed changing/deleting sequences when altering pre-Django 4.1 auto fields on PostgreSQL.

Thanks Anders Kaseorg for the report.

Follow up to 19e6efa50b.
Regression in 2eea361eff.

django/db/backends/postgresql/schema.py

@@ -130,6 +130,13 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             return using_sql
         return ""
 
+    def _get_sequence_name(self, table, column):
+        with self.connection.cursor() as cursor:
+            for sequence in self.connection.introspection.get_sequences(cursor, table):
+                if sequence["column"] == column:
+                    return sequence["name"]
+        return None
+
     def _alter_column_type_sql(self, model, old_field, new_field, new_type):
         # Drop indexes on varchar/text/citext columns that are changing to a
         # different type.
@@ -193,35 +200,38 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                 }
             )
             column = strip_quotes(new_field.column)
-            sequence_name = "%s_%s_seq" % (table, column)
             fragment, _ = super()._alter_column_type_sql(
                 model, old_field, new_field, new_type
             )
-            return fragment, [
+            # Drop the sequence if exists (Django 4.1+ identity columns don't
+            # have it).
+            other_actions = []
+            if sequence_name := self._get_sequence_name(table, column):
+                other_actions = [
                     (
-                    # Drop the sequence if exists (Django 4.1+ identity columns
-                    # don't have it).
                         self.sql_delete_sequence
                         % {
                             "sequence": self.quote_name(sequence_name),
                         },
                         [],
-                ),
+                    )
                 ]
+            return fragment, other_actions
         elif new_is_auto and old_is_auto and old_internal_type != new_internal_type:
             fragment, _ = super()._alter_column_type_sql(
                 model, old_field, new_field, new_type
             )
             column = strip_quotes(new_field.column)
-            sequence_name = f"{table}_{column}_seq"
             db_types = {
                 "AutoField": "integer",
                 "BigAutoField": "bigint",
                 "SmallAutoField": "smallint",
             }
-            return fragment, [
+            # Alter the sequence type if exists (Django 4.1+ identity columns
-                # Alter the sequence type if exists (Django 4.1+ identity
+            # don't have it).
-                # columns don't have it).
+            other_actions = []
+            if sequence_name := self._get_sequence_name(table, column):
+                other_actions = [
                     (
                         self.sql_alter_sequence_type
                         % {
@@ -231,6 +241,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                         [],
                     ),
                 ]
+            return fragment, other_actions
         else:
             return super()._alter_column_type_sql(model, old_field, new_field, new_type)
 

tests/schema/tests.py

@@ -1896,14 +1896,30 @@ class SchemaTests(TransactionTestCase):
             new_field.set_attributes_from_name("id")
             with connection.schema_editor() as editor:
                 editor.alter_field(SerialAutoField, old_field, new_field, strict=True)
+            sequence_name = f"{table}_{column}_seq"
             with connection.cursor() as cursor:
                 cursor.execute(
                     "SELECT data_type FROM pg_sequences WHERE sequencename = %s",
-                    [f"{table}_{column}_seq"],
+                    [sequence_name],
                 )
                 row = cursor.fetchone()
                 sequence_data_type = row[0] if row and row[0] else None
                 self.assertEqual(sequence_data_type, "bigint")
+            # Rename the column.
+            old_field = new_field
+            new_field = AutoField(primary_key=True)
+            new_field.model = SerialAutoField
+            new_field.set_attributes_from_name("renamed_id")
+            with connection.schema_editor() as editor:
+                editor.alter_field(SerialAutoField, old_field, new_field, strict=True)
+            with connection.cursor() as cursor:
+                cursor.execute(
+                    "SELECT data_type FROM pg_sequences WHERE sequencename = %s",
+                    [sequence_name],
+                )
+                row = cursor.fetchone()
+                sequence_data_type = row[0] if row and row[0] else None
+                self.assertEqual(sequence_data_type, "integer")
         finally:
             with connection.cursor() as cursor:
                 cursor.execute(f'DROP TABLE "{table}"')