Fixed #17653 -- Allowed using zero as AutoFields value on MySQL if NO_AUTO_VALUE_ON_ZERO SQL mode is enabled.

django/db/backends/base/features.py

@@ -100,7 +100,7 @@ class BaseDatabaseFeatures:
     # The database's limit on the number of query parameters.
     max_query_params = None
 
-    # Can an object have an autoincrement primary key of 0? MySQL says No.
+    # Can an object have an autoincrement primary key of 0?
     allows_auto_pk_0 = True
 
     # Do we need to NULL a ForeignKey out, or can the constraint check be

django/db/backends/mysql/features.py

@@ -17,7 +17,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_index_column_ordering = False
     supports_timezones = False
     requires_explicit_null_ordering_when_grouping = True
-    allows_auto_pk_0 = False
     can_release_savepoints = True
     atomic_transactions = False
     can_clone_databases = True
@@ -51,6 +50,14 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "Internal method used in Django tests. Don't rely on this from your code"
         return self.connection.mysql_server_data['default_storage_engine']
 
+    @cached_property
+    def allows_auto_pk_0(self):
+        """
+        Autoincrement primary key can be set to 0 if it doesn't generate new
+        autoincrement values.
+        """
+        return 'NO_AUTO_VALUE_ON_ZERO' in self.connection.sql_mode
+
     @cached_property
     def update_can_self_select(self):
         return self.connection.mysql_is_mariadb and self.connection.mysql_version >= (10, 3, 2)

django/db/backends/mysql/operations.py

@@ -227,8 +227,9 @@ class DatabaseOperations(BaseDatabaseOperations):
         ]
 
     def validate_autopk_value(self, value):
-        # MySQLism: zero in AUTO_INCREMENT field does not work. Refs #17653.
-        if value == 0:
+        # Zero in AUTO_INCREMENT field does not work without the
+        # NO_AUTO_VALUE_ON_ZERO SQL mode.
+        if value == 0 and not self.connection.features.allows_auto_pk_0:
             raise ValueError('The database backend does not accept 0 as a '
                              'value for AutoField.')
         return value
@@ -266,6 +267,9 @@ class DatabaseOperations(BaseDatabaseOperations):
     def max_name_length(self):
         return 64
 
+    def pk_default_value(self):
+        return 'NULL'
+
     def bulk_insert_sql(self, fields, placeholder_rows):
         placeholder_rows_sql = (", ".join(row) for row in placeholder_rows)
         values_sql = ", ".join("(%s)" % sql for sql in placeholder_rows_sql)