Create a model with a custom primary key field that is not an IntegerField? and another with a foreign key pointing to it:
class Author(models.Model):
id = models.PositiveIntegerField(primary_key=True)
name = models.CharField(max_length=200)
class Article(models.Model):
title = models.CharField(max_length=200)
author = models.ForeignKey(Author)
Let's see how the SQL looks:
BEGIN;
CREATE TABLE `dbtest_author` (
`id` integer UNSIGNED NOT NULL PRIMARY KEY,
`name` varchar(200) NOT NULL
)
;
CREATE TABLE `dbtest_article` (
`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
`title` varchar(200) NOT NULL,
`author_id` integer NOT NULL
)
;
ALTER TABLE `dbtest_article` ADD CONSTRAINT author_id_refs_id_6bbed69f FOREIGN KEY (`author_id`) REFERENCES `dbtest_author` (`id`);
CREATE INDEX `dbtest_article_author_id` ON `dbtest_article` (`author_id`);
COMMIT;
You can see that author_id should reference dbtest_author.id, but they have different data types.
Calling syncdb:
Creating table dbtest_author
Creating table dbtest_article
Traceback (most recent call last):
File "...manage.py", line 11, in <module>
execute_manager(settings)
File "C:\Programme\django_src\django\core\management\__init__.py", line 334, in execute_manager
utility.execute()
File "C:\Programme\django_src\django\core\management\__init__.py", line 295, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "C:\Programme\django_src\django\core\management\base.py", line 77, in run_from_argv
self.execute(*args, **options.__dict__)
File "C:\Programme\django_src\django\core\management\base.py", line 96, in execute
output = self.handle(*args, **options)
File "C:\Programme\django_src\django\core\management\base.py", line 178, in handle
return self.handle_noargs(**options)
File "C:\Programme\django_src\django\core\management\commands\syncdb.py", line 80, in handle_noargs
cursor.execute(statement)
File "C:\Programme\django_src\django\db\backends\util.py", line 19, in execute
return self.cursor.execute(sql, params)
File "C:\Programme\Python25\lib\site-packages\MySQLdb\cursors.py", line 166, in execute
self.errorhandler(self, exc, value)
File "C:\Programme\Python25\lib\site-packages\MySQLdb\connections.py", line 35, in defaulterrorhandler
raise errorclass, errorvalue
_mysql_exceptions.OperationalError: (1005, "Can't create table '.\\db\\#sql-5b4_8.frm' (errno: 150)")
MySQL is unable to add the constraint, because of the different types (integer, integer unsigned) used.
The problem goes back to [1970] where a foreign key pointing to an AutoField?, a PositiveIntegerField? or a PositiveSmallIntegerField? always becomes an IntegerField?.
