id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
26068	Django 1.8: KEY constraint for parent model missing in m2m [regression]	direx	nobody	"I am upgrading from 1.6 to 1.8 and while checking the SQL schema I found out that the SQL constraints created by Django 1.8 are different. Apparently there is one KEY constraint missing in m2m relations in Django 1.8 (tested using MySQL).

models.py:

{{{
from django.db import models

class Group(models.Model):
    name = models.CharField(max_length=100, db_index=True)

class User(models.Model):
    name = models.CharField(max_length=100, db_index=True)
    groups = models.ManyToManyField(Group)
}}}

SQL created by Django 1.6 (mysqldump output):
{{{
CREATE TABLE `myapp_user_groups` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `group_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `user_id` (`user_id`,`group_id`),
  KEY `myapp_user_groups_6340c63c` (`user_id`),
  KEY `myapp_user_groups_5f412f9a` (`group_id`),
  CONSTRAINT `group_id_refs_id_90b34ba9` FOREIGN KEY (`group_id`) REFERENCES `myapp_group` (`id`),
  CONSTRAINT `user_id_refs_id_ccc79bbf` FOREIGN KEY (`user_id`) REFERENCES `myapp_user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
}}}

SQL created by Django 1.8 (mysqldump output):
{{{
CREATE TABLE `myapp_user_groups` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `group_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `user_id` (`user_id`,`group_id`),
  KEY `myapp_user_groups_group_id_70cd7f8e20b5a3c3_fk_myapp_group_id` (`group_id`),
  CONSTRAINT `myapp_user_groups_group_id_70cd7f8e20b5a3c3_fk_myapp_group_id` FOREIGN KEY (`group_id`) REFERENCES `myapp_group` (`id`),
  CONSTRAINT `myapp_user_groups_user_id_dd075ee05371f3c_fk_myapp_user_id` FOREIGN KEY (`user_id`) REFERENCES `myapp_user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
}}}

Note that there is one '''KEY''' constraint missing in 1.8 f(`user_id`). The interesting thing is that `sqlall` looks the same in both Django versions:

{{{
BEGIN;
CREATE TABLE `myapp_group` (
    `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
    `name` varchar(100) NOT NULL
)
;
CREATE TABLE `myapp_user_groups` (
    `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
    `user_id` integer NOT NULL,
    `group_id` integer NOT NULL,
    UNIQUE (`user_id`, `group_id`)
)
;
ALTER TABLE `myapp_user_groups` ADD CONSTRAINT `group_id_refs_id_90b34ba9` FOREIGN KEY (`group_id`) REFERENCES `myapp_group` (`id`);
CREATE TABLE `myapp_user` (
    `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
    `name` varchar(100) NOT NULL
)
;
ALTER TABLE `myapp_user_groups` ADD CONSTRAINT `user_id_refs_id_ccc79bbf` FOREIGN KEY (`user_id`) REFERENCES `myapp_user` (`id`);
CREATE INDEX `myapp_group_4da47e07` ON `myapp_group` (`name`);
CREATE INDEX `myapp_user_groups_6340c63c` ON `myapp_user_groups` (`user_id`);
CREATE INDEX `myapp_user_groups_5f412f9a` ON `myapp_user_groups` (`group_id`);
CREATE INDEX `myapp_user_4da47e07` ON `myapp_user` (`name`);

COMMIT;
}}}

Using migrations in 1.8 does not change the behavior. It might also apply to other databases, "	Bug	closed	Database layer (models, ORM)	1.8	Normal	worksforme	mysql,m2m		Unreviewed	0	0	0	0	0	0