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
23379	sql_create generates incorrect SQL with synced database	flakfizer	Simon Charette	"The change between 1.6.6 to 1.7c3 in sql_create's first parameter from ""app"" to ""app_config"" is causing a bug, namely because app.get_models() returned a list, whereas app_config.get_models() returns a generator.  This causes the ""known_models"" set to be larger than it should be.

This bug will cause invalid sql - mysql, in my case - to be generated if tables already exist, as shown in the attached reproduction app.

1) python manage.py repro  # generates correct sql

{{{#!sql
CREATE TABLE `repro_app_a` (
    `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
    `b_id` integer NOT NULL
)
;
CREATE TABLE `repro_app_b` (
    `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
    `a_id` integer NOT NULL
)
;
ALTER TABLE `repro_app_b` ADD CONSTRAINT `a_id_refs_id_4838e71a` FOREIGN KEY (`a_id`) REFERENCES `repro_app_a` (`id`);
ALTER TABLE `repro_app_a` ADD CONSTRAINT `b_id_refs_id_b49a3179` FOREIGN KEY (`b_id`) REFERENCES `repro_app_b` (`id`);
}}}
2) python manage.py migrate
3) python manage.py repro  # generates incorrect sql; the first constraint fails because table repro_app_b hasn't been created yet.
{{{#!sql
CREATE TABLE `repro_app_a` (
    `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
    `b_id` integer NOT NULL
)
;
ALTER TABLE `repro_app_a` ADD CONSTRAINT `b_id_refs_id_b49a3179` FOREIGN KEY (`b_id`) REFERENCES `repro_app_b` (`id`);
CREATE TABLE `repro_app_b` (
    `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
    `a_id` integer NOT NULL
)
;
ALTER TABLE `repro_app_b` ADD CONSTRAINT `a_id_refs_id_4838e71a` FOREIGN KEY (`a_id`) REFERENCES `repro_app_a` (`id`);
}}}

Fortunately, the (or, ""a"") fix is an easy one-liner:

{{{
#!diff
--- a/django/core/management/sql.py
+++ b/django/core/management/sql.py
@@ -36,7 +36,7 @@ def sql_create(app_config, style, connection):
     # We trim models from the current app so that the sqlreset command does not
     # generate invalid SQL (leaving models out of known_models is harmless, so
     # we can be conservative).
-    app_models = app_config.get_models(include_auto_created=True)
+    app_models = set(app_config.get_models(include_auto_created=True))
     final_output = []
     tables = connection.introspection.table_names()
     known_models = set(model for model in connection.introspection.installed_models(tables) if model not in app_models)
}}}"	Bug	closed	Database layer (models, ORM)	1.7-rc-3	Release blocker	fixed			Ready for checkin	1	0	0	0	0	0