Fixed #30661 -- Added models.SmallAutoField.

17 files changed, 38 insertions, 12 deletions

diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index bb4b59e7c8..70878f92a2 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -143,9 +143,10 @@ class BaseDatabaseFeatures:
     # Can the backend introspect a TimeField, instead of a DateTimeField?
     can_introspect_time_field = True
 
-    # Some backends may not be able to differentiate BigAutoField from other
-    # fields such as AutoField.
+    # Some backends may not be able to differentiate BigAutoField or
+    # SmallAutoField from other fields such as AutoField.
     introspected_big_auto_field_type = 'BigAutoField'
+    introspected_small_auto_field_type = 'SmallAutoField'
 
     # Some backends may not be able to differentiate BooleanField from other
     # fields such as IntegerField.
diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index a5a4163c19..3540fd5d0d 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -182,7 +182,7 @@ class BaseDatabaseSchemaEditor:
             ))
             # Autoincrement SQL (for backends with post table definition
             # variant).
-            if field.get_internal_type() in ('AutoField', 'BigAutoField'):
+            if field.get_internal_type() in ('AutoField', 'BigAutoField', 'SmallAutoField'):
                 autoinc_sql = self.connection.ops.autoinc_sql(model._meta.db_table, field.column)
                 if autoinc_sql:
                     self.deferred_sql.extend(autoinc_sql)
diff --git a/django/db/backends/mysql/base.py b/django/db/backends/mysql/base.py
index 821f24fdf1..9a0ede0ac8 100644
--- a/django/db/backends/mysql/base.py
+++ b/django/db/backends/mysql/base.py
@@ -123,6 +123,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         'PositiveIntegerField': 'integer UNSIGNED',
         'PositiveSmallIntegerField': 'smallint UNSIGNED',
         'SlugField': 'varchar(%(max_length)s)',
+        'SmallAutoField': 'smallint AUTO_INCREMENT',
         'SmallIntegerField': 'smallint',
         'TextField': 'longtext',
         'TimeField': 'time(6)',
diff --git a/django/db/backends/mysql/introspection.py b/django/db/backends/mysql/introspection.py
index db1a387679..05e73c78dc 100644
--- a/django/db/backends/mysql/introspection.py
+++ b/django/db/backends/mysql/introspection.py
@@ -44,6 +44,8 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 return 'AutoField'
             elif field_type == 'BigIntegerField':
                 return 'BigAutoField'
+            elif field_type == 'SmallIntegerField':
+                return 'SmallAutoField'
         if description.is_unsigned:
             if field_type == 'IntegerField':
                 return 'PositiveIntegerField'
diff --git a/django/db/backends/mysql/operations.py b/django/db/backends/mysql/operations.py
index ef908ad8ae..e940286720 100644
--- a/django/db/backends/mysql/operations.py
+++ b/django/db/backends/mysql/operations.py
@@ -19,6 +19,7 @@ class DatabaseOperations(BaseDatabaseOperations):
     cast_data_types = {
         'AutoField': 'signed integer',
         'BigAutoField': 'signed integer',
+        'SmallAutoField': 'signed integer',
         'CharField': 'char(%(max_length)s)',
         'DecimalField': 'decimal(%(max_digits)s, %(decimal_places)s)',
         'TextField': 'char',
diff --git a/django/db/backends/oracle/base.py b/django/db/backends/oracle/base.py
index 0fbe96ab9b..ef33d9fad7 100644
--- a/django/db/backends/oracle/base.py
+++ b/django/db/backends/oracle/base.py
@@ -123,6 +123,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         'PositiveIntegerField': 'NUMBER(11)',
         'PositiveSmallIntegerField': 'NUMBER(11)',
         'SlugField': 'NVARCHAR2(%(max_length)s)',
+        'SmallAutoField': 'NUMBER(5) GENERATED BY DEFAULT ON NULL AS IDENTITY',
         'SmallIntegerField': 'NUMBER(11)',
         'TextField': 'NCLOB',
         'TimeField': 'TIMESTAMP',
diff --git a/django/db/backends/oracle/introspection.py b/django/db/backends/oracle/introspection.py
index 1fcba05510..2322ae0b5d 100644
--- a/django/db/backends/oracle/introspection.py
+++ b/django/db/backends/oracle/introspection.py
@@ -35,6 +35,8 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
             if scale == 0:
                 if precision > 11:
                     return 'BigAutoField' if description.is_autofield else 'BigIntegerField'
+                elif 1 < precision < 6 and description.is_autofield:
+                    return 'SmallAutoField'
                 elif precision == 1:
                     return 'BooleanField'
                 elif description.is_autofield:
diff --git a/django/db/backends/oracle/operations.py b/django/db/backends/oracle/operations.py
index 77c568e84b..016d4c9a59 100644
--- a/django/db/backends/oracle/operations.py
+++ b/django/db/backends/oracle/operations.py
@@ -56,6 +56,7 @@ END;
     cast_data_types = {
         'AutoField': 'NUMBER(11)',
         'BigAutoField': 'NUMBER(19)',
+        'SmallAutoField': 'NUMBER(5)',
         'TextField': cast_char_field_without_max_length,
     }
 
diff --git a/django/db/backends/oracle/schema.py b/django/db/backends/oracle/schema.py
index 3356788a82..d0f664a6ff 100644
--- a/django/db/backends/oracle/schema.py
+++ b/django/db/backends/oracle/schema.py
@@ -90,7 +90,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         # Make a new field that's like the new one but with a temporary
         # column name.
         new_temp_field = copy.deepcopy(new_field)
-        new_temp_field.null = (new_field.get_internal_type() not in ('AutoField', 'BigAutoField'))
+        new_temp_field.null = (new_field.get_internal_type() not in ('AutoField', 'BigAutoField', 'SmallAutoField'))
         new_temp_field.column = self._generate_temp_name(new_field.column)
         # Add it
         self.add_field(model, new_temp_field)
diff --git a/django/db/backends/postgresql/base.py b/django/db/backends/postgresql/base.py
index 7e34a3a177..eea8aeb135 100644
--- a/django/db/backends/postgresql/base.py
+++ b/django/db/backends/postgresql/base.py
@@ -92,6 +92,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         'PositiveIntegerField': 'integer',
         'PositiveSmallIntegerField': 'smallint',
         'SlugField': 'varchar(%(max_length)s)',
+        'SmallAutoField': 'smallserial',
         'SmallIntegerField': 'smallint',
         'TextField': 'text',
         'TimeField': 'time',
diff --git a/django/db/backends/postgresql/introspection.py b/django/db/backends/postgresql/introspection.py
index 1c9c7e63a5..b7bf18691c 100644
--- a/django/db/backends/postgresql/introspection.py
+++ b/django/db/backends/postgresql/introspection.py
@@ -37,6 +37,8 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 return 'AutoField'
             elif field_type == 'BigIntegerField':
                 return 'BigAutoField'
+            elif field_type == 'SmallIntegerField':
+                return 'SmallAutoField'
         return field_type
 
     def get_table_list(self, cursor):
diff --git a/django/db/backends/postgresql/operations.py b/django/db/backends/postgresql/operations.py
index 0c497edf71..61bac5e55a 100644
--- a/django/db/backends/postgresql/operations.py
+++ b/django/db/backends/postgresql/operations.py
@@ -11,6 +11,7 @@ class DatabaseOperations(BaseDatabaseOperations):
     cast_data_types = {
         'AutoField': 'integer',
         'BigAutoField': 'bigint',
+        'SmallAutoField': 'smallint',
     }
 
     def unification_cast_sql(self, output_field):
diff --git a/django/db/backends/postgresql/schema.py b/django/db/backends/postgresql/schema.py
index b7f52ccf25..eb5b182680 100644
--- a/django/db/backends/postgresql/schema.py
+++ b/django/db/backends/postgresql/schema.py
@@ -69,15 +69,15 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             self.sql_alter_column_type += ' USING %(column)s::%(type)s'
         # Make ALTER TYPE with SERIAL make sense.
         table = strip_quotes(model._meta.db_table)
-        if new_type.lower() in ("serial", "bigserial"):
+        serial_fields_map = {'bigserial': 'bigint', 'serial': 'integer', 'smallserial': 'smallint'}
+        if new_type.lower() in serial_fields_map:
             column = strip_quotes(new_field.column)
             sequence_name = "%s_%s_seq" % (table, column)
-            col_type = "integer" if new_type.lower() == "serial" else "bigint"
             return (
                 (
                     self.sql_alter_column_type % {
                         "column": self.quote_name(column),
-                        "type": col_type,
+                        "type": serial_fields_map[new_type.lower()],
                     },
                     [],
                 ),
diff --git a/django/db/backends/sqlite3/base.py b/django/db/backends/sqlite3/base.py
index fff65197f9..7a4439ae88 100644
--- a/django/db/backends/sqlite3/base.py
+++ b/django/db/backends/sqlite3/base.py
@@ -104,6 +104,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         'PositiveIntegerField': 'integer unsigned',
         'PositiveSmallIntegerField': 'smallint unsigned',
         'SlugField': 'varchar(%(max_length)s)',
+        'SmallAutoField': 'integer',
         'SmallIntegerField': 'smallint',
         'TextField': 'text',
         'TimeField': 'time',
@@ -116,6 +117,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
     data_types_suffix = {
         'AutoField': 'AUTOINCREMENT',
         'BigAutoField': 'AUTOINCREMENT',
+        'SmallAutoField': 'AUTOINCREMENT',
     }
     # SQLite requires LIKE statements to include an ESCAPE clause if the value
     # being escaped has a percent or underscore in it.
diff --git a/django/db/backends/sqlite3/features.py b/django/db/backends/sqlite3/features.py
index 3d52a8036f..18b76f8c86 100644
--- a/django/db/backends/sqlite3/features.py
+++ b/django/db/backends/sqlite3/features.py
@@ -19,6 +19,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     can_introspect_positive_integer_field = True
     can_introspect_small_integer_field = True
     introspected_big_auto_field_type = 'AutoField'
+    introspected_small_auto_field_type = 'AutoField'
     supports_transactions = True
     atomic_transactions = False
     can_rollback_ddl = True
diff --git a/django/db/backends/sqlite3/introspection.py b/django/db/backends/sqlite3/introspection.py
index faf9328415..5e33d2a7e2 100644
--- a/django/db/backends/sqlite3/introspection.py
+++ b/django/db/backends/sqlite3/introspection.py
@@ -57,9 +57,9 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
 
     def get_field_type(self, data_type, description):
         field_type = super().get_field_type(data_type, description)
-        if description.pk and field_type in {'BigIntegerField', 'IntegerField'}:
-            # No support for BigAutoField as SQLite treats all integer primary
-            # keys as signed 64-bit integers.
+        if description.pk and field_type in {'BigIntegerField', 'IntegerField', 'SmallIntegerField'}:
+            # No support for BigAutoField or SmallAutoField as SQLite treats
+            # all integer primary keys as signed 64-bit integers.
             return 'AutoField'
         return field_type
 
diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 1388dffc58..ff686e4f62 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -38,8 +38,8 @@ __all__ = [
     'EmailField', 'Empty', 'Field', 'FieldDoesNotExist', 'FilePathField',
     'FloatField', 'GenericIPAddressField', 'IPAddressField', 'IntegerField',
     'NOT_PROVIDED', 'NullBooleanField', 'PositiveIntegerField',
-    'PositiveSmallIntegerField', 'SlugField', 'SmallIntegerField', 'TextField',
-    'TimeField', 'URLField', 'UUIDField',
+    'PositiveSmallIntegerField', 'SlugField', 'SmallAutoField',
+    'SmallIntegerField', 'TextField', 'TimeField', 'URLField', 'UUIDField',
 ]
 
 
@@ -985,6 +985,16 @@ class BigAutoField(AutoField):
         return BigIntegerField().db_type(connection=connection)
 
 
+class SmallAutoField(AutoField):
+    description = _('Small integer')
+
+    def get_internal_type(self):
+        return 'SmallAutoField'
+
+    def rel_db_type(self, connection):
+        return SmallIntegerField().db_type(connection=connection)
+
+
 class BooleanField(Field):
     empty_strings_allowed = False
     default_error_messages = {