#24435: Removing blank=True, null=True from ManyToMany field causes data
deletion
in migration
--------------------------+------------------------------------------------
Reporter: | Owner: nobody
marktranchant |
Type: Bug | Status: new
Component: | Version: 1.7
Migrations |
Severity: Normal | Keywords: m2m migrations deletion blank null
Triage Stage: | Has patch: 0
Unreviewed |
Easy pickings: 0 | UI/UX: 0
--------------------------+------------------------------------------------
My app has a Group model with an m2m field in it which used to look like:
{{{ things = models.ManyToManyField(Thing, blank=True, null=True) }}}
Django 1.8a1 on my test environment warned me that the {{{blank}}} and
{{{null}}} arguments were unnecessary, so I removed them:
{{{ things = models.ManyToManyField(Thing) }}}
Then I ran {{{manage.py makemigrations}}} and applied the resulting
migration with {{{manage.py migrate}}}. To my horror, the data in the
relevant "linking" table was all deleted.
The section from the migration file looks like this:
{{{
operations = [
migrations.RemoveField(
model_name='group',
name='things',
),
migrations.AddField(
model_name='group',
name='things',
field=models.ManyToManyField(to='sa.Thing'),
),
]
}}}
This doesn't look like the right behaviour to me, and cost me a lot of
time recovering data from backup. Have I done something wrong (other than
trusting the migration file without inspecting it) or is this a genuine
bug?
--
Ticket URL: <https://code.djangoproject.com/ticket/24435>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
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