Fixed #30511 -- Used identity columns instead of serials on PostgreSQL.

1 files changed, 30 insertions, 56 deletions

diff --git a/django/db/backends/postgresql/schema.py b/django/db/backends/postgresql/schema.py
index 73e2749020..3053c8d370 100644
--- a/django/db/backends/postgresql/schema.py
+++ b/django/db/backends/postgresql/schema.py
@@ -7,12 +7,7 @@ from django.db.backends.utils import strip_quotes
 
 class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
 
-    sql_create_sequence = "CREATE SEQUENCE %(sequence)s"
     sql_delete_sequence = "DROP SEQUENCE IF EXISTS %(sequence)s CASCADE"
-    sql_set_sequence_max = (
-        "SELECT setval('%(sequence)s', MAX(%(column)s)) FROM %(table)s"
-    )
-    sql_set_sequence_owner = "ALTER SEQUENCE %(sequence)s OWNED BY %(table)s.%(column)s"
 
     sql_create_index = (
         "CREATE INDEX %(name)s ON %(table)s%(using)s "
@@ -39,6 +34,14 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
     )
     sql_delete_procedure = "DROP FUNCTION %(procedure)s(%(param_types)s)"
 
+    sql_add_identity = (
+        "ALTER TABLE %(table)s ALTER COLUMN %(column)s ADD "
+        "GENERATED BY DEFAULT AS IDENTITY"
+    )
+    sql_drop_indentity = (
+        "ALTER TABLE %(table)s ALTER COLUMN %(column)s DROP IDENTITY IF EXISTS"
+    )
+
     def quote_value(self, value):
         if isinstance(value, str):
             value = value.replace("%", "%%")
@@ -116,78 +119,47 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                 self.sql_alter_column_type += using_sql
         elif self._field_data_type(old_field) != self._field_data_type(new_field):
             self.sql_alter_column_type += using_sql
-        # Make ALTER TYPE with SERIAL make sense.
+        # Make ALTER TYPE with IDENTITY make sense.
         table = strip_quotes(model._meta.db_table)
-        serial_fields_map = {
-            "bigserial": "bigint",
-            "serial": "integer",
-            "smallserial": "smallint",
+        auto_field_types = {
+            "AutoField",
+            "BigAutoField",
+            "SmallAutoField",
         }
-        if new_type.lower() in serial_fields_map:
+        old_is_auto = old_internal_type in auto_field_types
+        new_is_auto = new_internal_type in auto_field_types
+        if new_is_auto and not old_is_auto:
             column = strip_quotes(new_field.column)
-            sequence_name = "%s_%s_seq" % (table, column)
             return (
                 (
                     self.sql_alter_column_type
                     % {
                         "column": self.quote_name(column),
-                        "type": serial_fields_map[new_type.lower()],
+                        "type": new_type,
                     },
                     [],
                 ),
                 [
                     (
-                        self.sql_delete_sequence
-                        % {
-                            "sequence": self.quote_name(sequence_name),
-                        },
-                        [],
-                    ),
-                    (
-                        self.sql_create_sequence
-                        % {
-                            "sequence": self.quote_name(sequence_name),
-                        },
-                        [],
-                    ),
-                    (
-                        self.sql_alter_column
-                        % {
-                            "table": self.quote_name(table),
-                            "changes": self.sql_alter_column_default
-                            % {
-                                "column": self.quote_name(column),
-                                "default": "nextval('%s')"
-                                % self.quote_name(sequence_name),
-                            },
-                        },
-                        [],
-                    ),
-                    (
-                        self.sql_set_sequence_max
+                        self.sql_add_identity
                         % {
                             "table": self.quote_name(table),
                             "column": self.quote_name(column),
-                            "sequence": self.quote_name(sequence_name),
-                        },
-                        [],
-                    ),
-                    (
-                        self.sql_set_sequence_owner
-                        % {
-                            "table": self.quote_name(table),
-                            "column": self.quote_name(column),
-                            "sequence": self.quote_name(sequence_name),
                         },
                         [],
                     ),
                 ],
             )
-        elif (
-            old_field.db_parameters(connection=self.connection)["type"]
-            in serial_fields_map
-        ):
-            # Drop the sequence if migrating away from AutoField.
+        elif old_is_auto and not new_is_auto:
+            # Drop IDENTITY if exists (pre-Django 4.1 serial columns don't have
+            # it).
+            self.execute(
+                self.sql_drop_indentity
+                % {
+                    "table": self.quote_name(table),
+                    "column": self.quote_name(strip_quotes(old_field.column)),
+                }
+            )
             column = strip_quotes(new_field.column)
             sequence_name = "%s_%s_seq" % (table, column)
             fragment, _ = super()._alter_column_type_sql(
@@ -195,6 +167,8 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             )
             return fragment, [
                 (
+                    # Drop the sequence if exists (Django 4.1+ identity columns
+                    # don't have it).
                     self.sql_delete_sequence
                     % {
                         "sequence": self.quote_name(sequence_name),