[patch] magic-removal: MySQL does not support DROP CONSTRAINT

[Jan Rademaker <j.rademaker@…>]

Although MySQL 4 & 5 support ADD CONSTRAINT they don't support DROP CONSTRAINT. This causes manage sqlreset [app] and manage sqlclear [app] to produce invalid sql statements.

MySQL MaxDB, however, _does_ support DROP CONSTRAINT.

See #1082 also.

[pb@…]

I'm not attaching this as a patch file because it's a hack, not a fix, but if you just need to get sqlreset and sqlclear working with &!@$# MySQL today, then:

Index: django/db/backends/mysql/base.py
===================================================================
--- django/db/backends/mysql/base.py    (revision 2545)
+++ django/db/backends/mysql/base.py    (working copy)
@@ -86,7 +86,7 @@
             self.connection.close()
             self.connection = None
 
-supports_constraints = True
+supports_constraints = False
 
 def quote_name(name):
     if name.startswith("`") and name.endswith("`"):

A slightly more granular fix would be to break down this attribute into supports_constraint_add and supports_constraint_drop, then make the appropriate updates in the backend files. The differences between MySQL MaxDB will still need to be addressed, though.

[Russell Cloran <russell@…>]

I'm having a similar problem. (At the moment worked around by ./manage.py sqlreset app | sed 's/DROP CONSTRAINT/DROP FOREIGN KEY/' | mysql). I have no idea how to fix it, just thought some confirmation would be good :)

[Geert Vanderkelen <geert@…>]

I'm attaching a patch which fixes this problem. It will use the 'get_foreignkey_drop' function from the backend module so different syntax is supported. In MySQL this is ALTER TABLE <table> DROP FOREIGN KEY <name>;.

I took the liberty to also add these functions to the other backends, but I couldn't test those. Although I think it should work fine, might be good to test them ;)

I put severity to major, since this basicly makes the sqlreset for example, not work for MySQL.

[Adrian Holovaty]

(In [2732]) magic-removal: Fixed #1373 -- Factored out database-specific 'DROP CONSTRAINT' syntax, to get sqlreset/sqlclear working with MySQL. Thanks, njharman