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

7 files changed, 90 insertions, 95 deletions

diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index a140a6dc61..3a45b70311 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -904,6 +904,9 @@ class BaseDatabaseSchemaEditor:
         actions = []
         null_actions = []
         post_actions = []
+        # Type suffix change? (e.g. auto increment).
+        old_type_suffix = old_field.db_type_suffix(connection=self.connection)
+        new_type_suffix = new_field.db_type_suffix(connection=self.connection)
         # Collation change?
         old_collation = getattr(old_field, "db_collation", None)
         new_collation = getattr(new_field, "db_collation", None)
@@ -914,7 +917,7 @@ class BaseDatabaseSchemaEditor:
             )
             actions.append(fragment)
         # Type change?
-        elif old_type != new_type:
+        elif (old_type, old_type_suffix) != (new_type, new_type_suffix):
             fragment, other_actions = self._alter_column_type_sql(
                 model, old_field, new_field, new_type
             )
diff --git a/django/db/backends/postgresql/base.py b/django/db/backends/postgresql/base.py
index 630da22964..2758c402ab 100644
--- a/django/db/backends/postgresql/base.py
+++ b/django/db/backends/postgresql/base.py
@@ -72,8 +72,8 @@ class DatabaseWrapper(BaseDatabaseWrapper):
     # be interpolated against the values of Field.__dict__ before being output.
     # If a column type is set to None, it won't be included in the output.
     data_types = {
-        "AutoField": "serial",
-        "BigAutoField": "bigserial",
+        "AutoField": "integer",
+        "BigAutoField": "bigint",
         "BinaryField": "bytea",
         "BooleanField": "boolean",
         "CharField": "varchar(%(max_length)s)",
@@ -94,7 +94,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         "PositiveIntegerField": "integer",
         "PositiveSmallIntegerField": "smallint",
         "SlugField": "varchar(%(max_length)s)",
-        "SmallAutoField": "smallserial",
+        "SmallAutoField": "smallint",
         "SmallIntegerField": "smallint",
         "TextField": "text",
         "TimeField": "time",
@@ -105,6 +105,11 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         "PositiveIntegerField": '"%(column)s" >= 0',
         "PositiveSmallIntegerField": '"%(column)s" >= 0',
     }
+    data_types_suffix = {
+        "AutoField": "GENERATED BY DEFAULT AS IDENTITY",
+        "BigAutoField": "GENERATED BY DEFAULT AS IDENTITY",
+        "SmallAutoField": "GENERATED BY DEFAULT AS IDENTITY",
+    }
     operators = {
         "exact": "= %s",
         "iexact": "= UPPER(%s)",
diff --git a/django/db/backends/postgresql/introspection.py b/django/db/backends/postgresql/introspection.py
index 16d80663aa..921501a4a3 100644
--- a/django/db/backends/postgresql/introspection.py
+++ b/django/db/backends/postgresql/introspection.py
@@ -1,10 +1,12 @@
-from django.db.backends.base.introspection import (
-    BaseDatabaseIntrospection,
-    FieldInfo,
-    TableInfo,
-)
+from collections import namedtuple
+
+from django.db.backends.base.introspection import BaseDatabaseIntrospection
+from django.db.backends.base.introspection import FieldInfo as BaseFieldInfo
+from django.db.backends.base.introspection import TableInfo
 from django.db.models import Index
 
+FieldInfo = namedtuple("FieldInfo", BaseFieldInfo._fields + ("is_autofield",))
+
 
 class DatabaseIntrospection(BaseDatabaseIntrospection):
     # Maps type codes to Django Field types.
@@ -37,7 +39,11 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
 
     def get_field_type(self, data_type, description):
         field_type = super().get_field_type(data_type, description)
-        if description.default and "nextval" in description.default:
+        if description.is_autofield or (
+            # Required for pre-Django 4.1 serial columns.
+            description.default
+            and "nextval" in description.default
+        ):
             if field_type == "IntegerField":
                 return "AutoField"
             elif field_type == "BigIntegerField":
@@ -84,7 +90,8 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 a.attname AS column_name,
                 NOT (a.attnotnull OR (t.typtype = 'd' AND t.typnotnull)) AS is_nullable,
                 pg_get_expr(ad.adbin, ad.adrelid) AS column_default,
-                CASE WHEN collname = 'default' THEN NULL ELSE collname END AS collation
+                CASE WHEN collname = 'default' THEN NULL ELSE collname END AS collation,
+                a.attidentity != '' AS is_autofield
             FROM pg_attribute a
             LEFT JOIN pg_attrdef ad ON a.attrelid = ad.adrelid AND a.attnum = ad.adnum
             LEFT JOIN pg_collation co ON a.attcollation = co.oid
@@ -118,23 +125,21 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
     def get_sequences(self, cursor, table_name, table_fields=()):
         cursor.execute(
             """
-            SELECT s.relname as sequence_name, col.attname
-            FROM pg_class s
-                JOIN pg_namespace sn ON sn.oid = s.relnamespace
-                JOIN
-                    pg_depend d ON d.refobjid = s.oid
+            SELECT
+                s.relname AS sequence_name,
+                a.attname AS colname
+            FROM
+                pg_class s
+                JOIN pg_depend d ON d.objid = s.oid
+                    AND d.classid = 'pg_class'::regclass
                     AND d.refclassid = 'pg_class'::regclass
-                JOIN
-                    pg_attrdef ad ON ad.oid = d.objid
-                    AND d.classid = 'pg_attrdef'::regclass
-                JOIN
-                    pg_attribute col ON col.attrelid = ad.adrelid
-                    AND col.attnum = ad.adnum
-                JOIN pg_class tbl ON tbl.oid = ad.adrelid
-            WHERE s.relkind = 'S'
-              AND d.deptype in ('a', 'n')
-              AND pg_catalog.pg_table_is_visible(tbl.oid)
-              AND tbl.relname = %s
+                JOIN pg_attribute a ON d.refobjid = a.attrelid
+                    AND d.refobjsubid = a.attnum
+                JOIN pg_class tbl ON tbl.oid = d.refobjid
+                    AND tbl.relname = %s
+                    AND pg_catalog.pg_table_is_visible(tbl.oid)
+            WHERE
+                s.relkind = 'S';
         """,
             [table_name],
         )
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),
diff --git a/docs/releases/4.1.txt b/docs/releases/4.1.txt
index 2ec0d42cdd..71f88eefdb 100644
--- a/docs/releases/4.1.txt
+++ b/docs/releases/4.1.txt
@@ -309,6 +309,9 @@ Models
   allows customizing attributes of fields that don't affect a column
   definition.
 
+* On PostgreSQL, ``AutoField``, ``BigAutoField``, and ``SmallAutoField`` are
+  now created as identity columns rather than serial columns with sequences.
+
 Requests and Responses
 ~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/tests/backends/postgresql/test_introspection.py b/tests/backends/postgresql/test_introspection.py
index dc95d6ad23..2dfb7514d6 100644
--- a/tests/backends/postgresql/test_introspection.py
+++ b/tests/backends/postgresql/test_introspection.py
@@ -27,3 +27,18 @@ class DatabaseSequenceTests(TestCase):
                 seqs,
                 [{"table": Person._meta.db_table, "column": "id", "name": "pers_seq"}],
             )
+
+    def test_get_sequences_old_serial(self):
+        with connection.cursor() as cursor:
+            cursor.execute("CREATE TABLE testing (serial_field SERIAL);")
+            seqs = connection.introspection.get_sequences(cursor, "testing")
+            self.assertEqual(
+                seqs,
+                [
+                    {
+                        "table": "testing",
+                        "column": "serial_field",
+                        "name": "testing_serial_field_seq",
+                    }
+                ],
+            )
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index c758db8bc8..049e604480 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -1570,11 +1570,7 @@ class SchemaTests(TransactionTestCase):
         Author.objects.create(name="Foo")
         Author.objects.create(name="Bar")
 
-    def test_alter_autofield_pk_to_bigautofield_pk_sequence_owner(self):
-        """
-        Converting an implicit PK to BigAutoField(primary_key=True) should keep
-        a sequence owner on PostgreSQL.
-        """
+    def test_alter_autofield_pk_to_bigautofield_pk(self):
         with connection.schema_editor() as editor:
             editor.create_model(Author)
         old_field = Author._meta.get_field("id")
@@ -1591,14 +1587,9 @@ class SchemaTests(TransactionTestCase):
             )
             if sequence_reset_sqls:
                 cursor.execute(sequence_reset_sqls[0])
-        # Fail on PostgreSQL if sequence is missing an owner.
         self.assertIsNotNone(Author.objects.create(name="Bar"))
 
-    def test_alter_autofield_pk_to_smallautofield_pk_sequence_owner(self):
-        """
-        Converting an implicit PK to SmallAutoField(primary_key=True) should
-        keep a sequence owner on PostgreSQL.
-        """
+    def test_alter_autofield_pk_to_smallautofield_pk(self):
         with connection.schema_editor() as editor:
             editor.create_model(Author)
         old_field = Author._meta.get_field("id")
@@ -1615,7 +1606,6 @@ class SchemaTests(TransactionTestCase):
             )
             if sequence_reset_sqls:
                 cursor.execute(sequence_reset_sqls[0])
-        # Fail on PostgreSQL if sequence is missing an owner.
         self.assertIsNotNone(Author.objects.create(name="Bar"))
 
     def test_alter_int_pk_to_autofield_pk(self):