Renaming a model field that has null=False makes it nullable in MySQL

[murfi]

Steps to reproduce:

1. Create a simple model:

   class TestModel(models.Model):
           value_a = models.IntegerField(null=False)
   

2. ./manage.py makemigrations
3. ./manage.py migrate
4. So far so good:

   mysql> describe testy_testmodel;
   +---------+---------+------+-----+---------+----------------+
   | Field   | Type    | Null | Key | Default | Extra          |
   +---------+---------+------+-----+---------+----------------+
   | id      | int(11) | NO   | PRI | NULL    | auto_increment |
   | value_a | int(11) | NO   |     | NULL    |                |
   +---------+---------+------+-----+---------+----------------+
   2 rows in set (0.00 sec)
   

5. Change model field name value_a -> value_b:

   class TestModel(models.model):
           value_b = models.IntegerField(null=False)
   

6. ./manage.py makemigrations
7. ./manage.py migrate
8. NOT NULL for value_b has been lost:

   mysql> describe testy_testmodel;
   +---------+---------+------+-----+---------+----------------+
   | Field   | Type    | Null | Key | Default | Extra          |
   +---------+---------+------+-----+---------+----------------+
   | id      | int(11) | NO   | PRI | NULL    | auto_increment |
   | value_b | int(11) | YES  |     | NULL    |                |
   +---------+---------+------+-----+---------+----------------+
   2 rows in set (0.00 sec)
   

The ALTER-statement django produces is

ALTER TABLE `testy_testmodel` CHANGE `value_a` `value_b` integer;

...and it should contain the NOT NULL, but it doesn't.

Edit: Similar bug when changing field type was fixed in #24595. The bug is still present in 1.8.1 when renaming a field.

[Alasdair Nicol]

This looks like a duplicate of #24595, which is fixed in 1.7.8 and 1.8.1.

[murfi]

True the comment in the end related to changing field type was invalid and fixed in #24595. The example case is still reproducible with Django==1.8.1.

[Alasdair Nicol]

Apologies for incorrectly closing as a duplicate before. I can reproduce in Django 1.7.8, 1.8.1 and master.

[Claude Paroz]

We've missed the rename use case while fixing #24595 :-(

[Andriy Sokolovskiy]

Test to reproduce the issue

[Andriy Sokolovskiy]

I just attached a patch with tests which reproduces the issue.
I'm also working on fixing issue

[Andriy Sokolovskiy]

​https://github.com/django/django/pull/4714

[Andriy Sokolovskiy]

PR against master - ​https://github.com/django/django/pull/4715

[Tim Graham]

Claude, look good to you?

[Claude Paroz]

Yes, sure! Thanks Andriy.

[Tim Graham <timograham@…>]

In 80ad547:

Fixed #24817 -- Prevented loss of null info in MySQL field renaming.

[Tim Graham <timograham@…>]

In f65d4db:

[1.8.x] Fixed #24817 -- Prevented loss of null info in MySQL field renaming.

Backport of 80ad5472ce4b6ba6e94227422d0727371e97cdf0 from master

[Tim Graham <timograham@…>]

In 927d90ee:

[1.7.x] Fixed #24817 -- Prevented loss of null info in MySQL field renaming.

Backport of 80ad5472ce4b6ba6e94227422d0727371e97cdf0 from master