#31788: Models migration with change field foreign to many and deleting unique
together.
----------------------------+------------------------------------
Reporter: budzichd | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 3.0
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
----------------------------+------------------------------------
Old description:
> I have models like
>
> {{{
> class Authors(models.Model):
>
> project_data_set = models.ManyToManyField(
> ProjectDataSet,
> on_delete=models.PROTECT
> )
> state = models.IntegerField()
> start_date = models.DateField()
>
> class Meta:
> unique_together = (('project_data_set', 'state', 'start_date'),)
> }}}
>
> and
>
> {{{
> class DataSet(models.Model):
> name = models.TextField(max_length=50)
>
> class Project(models.Model):
> data_sets = models.ManyToManyField(
> DataSet,
> through='ProjectDataSet',
> )
> name = models.TextField(max_length=50)
>
> class ProjectDataSet(models.Model):
> """
> Cross table of data set and project
> """
> data_set = models.ForeignKey(DataSet, on_delete=models.PROTECT)
> project = models.ForeignKey(Project, on_delete=models.PROTECT)
>
> class Meta:
> unique_together = (('data_set', 'project'),)
> }}}
>
> when i want to change field project_data_set in Authors model from
> foreign key field to many to many field I must delete a unique_together,
> cause it can't be on many to many field.
> Then my model should be like:
>
> {{{
> class Authors(models.Model):
>
> project_data_set = models.ManyToManyField(
> ProjectDataSet,
> )
>
> state = models.IntegerField()
> start_date = models.DateField()
> }}}
>
> But when I want to do a migrations.
> 1. python3 manage.py makemigrations
> 2. python3 manage.py migrate
> I have error:
> {{{ValueError: Found wrong number (0) of constraints for
> app_authors(project_data_set, state, start_date)}}}
> The database is on production, so I can't delete previous initial
> migrations, and this error isn't depending on database, cause I delete it
> and error is still the same.
> My solve is to first delete unique_together, then do a makemigrations and
> then migrate. After that change the field from foreign key to many to
> many field, then do a makemigrations and then migrate.
> But in this way I have 2 migrations instead of one.
>
> I added attachment with this project, download it and then do
> makemigrations and then migrate to see this error.
New description:
I have models like
{{{#!python
class Authors(models.Model):
project_data_set = models.ForeignKey(
ProjectDataSet,
on_delete=models.PROTECT
)
state = models.IntegerField()
start_date = models.DateField()
class Meta:
unique_together = (('project_data_set', 'state', 'start_date'),)
}}}
and
{{{
class DataSet(models.Model):
name = models.TextField(max_length=50)
class Project(models.Model):
data_sets = models.ManyToManyField(
DataSet,
through='ProjectDataSet',
)
name = models.TextField(max_length=50)
class ProjectDataSet(models.Model):
"""
Cross table of data set and project
"""
data_set = models.ForeignKey(DataSet, on_delete=models.PROTECT)
project = models.ForeignKey(Project, on_delete=models.PROTECT)
class Meta:
unique_together = (('data_set', 'project'),)
}}}
when i want to change field project_data_set in Authors model from foreign
key field to many to many field I must delete a unique_together, cause it
can't be on many to many field.
Then my model should be like:
{{{
class Authors(models.Model):
project_data_set = models.ManyToManyField(
ProjectDataSet,
)
state = models.IntegerField()
start_date = models.DateField()
}}}
But when I want to do a migrations.
1. python3 manage.py makemigrations
2. python3 manage.py migrate
I have error:
{{{ValueError: Found wrong number (0) of constraints for
app_authors(project_data_set, state, start_date)}}}
The database is on production, so I can't delete previous initial
migrations, and this error isn't depending on database, cause I delete it
and error is still the same.
My solve is to first delete unique_together, then do a makemigrations and
then migrate. After that change the field from foreign key to many to many
field, then do a makemigrations and then migrate.
But in this way I have 2 migrations instead of one.
I added attachment with this project, download it and then do
makemigrations and then migrate to see this error.
--
Comment (by Simon Charette):
I agree that you'll loose data but `Alter(Index|Unique)Together` should
always be sorted before `RemoveField`
https://github.com/django/django/blob/b502061027b90499f2e20210f944292cecd74d24/django/db/migrations/autodetector.py#L910
https://github.com/django/django/blob/b502061027b90499f2e20210f944292cecd74d24/django/db/migrations/autodetector.py#L424-L430
So something's broken here in a few different ways and I suspect it's due
to the fact the same field name `project_data_set` is reused for the many-
to-many field.
If you start from
{{{#!python
class Authors(models.Model):
project_data_set = models.ForeignKey(
ProjectDataSet,
on_delete=models.PROTECT
)
state = models.IntegerField()
start_date = models.DateField()
class Meta:
unique_together = (('project_data_set', 'state', 'start_date'),)
}}}
And generate `makemigrations` for
{{{#!python
class Authors(models.Model):
project_data_set = models.ManyToManyField(ProjectDataSet)
state = models.IntegerField()
start_date = models.DateField()
}}}
You'll get two migrations with the following operations
{{{#!python
# 0002
operations = [
migrations.AddField(
model_name='authors',
name='project_data_set',
field=models.ManyToManyField(to='ticket_31788.ProjectDataSet'),
),
migrations.AlterUniqueTogether(
name='authors',
unique_together=set(),
),
migrations.RemoveField(
model_name='authors',
name='project_data_set',
),
]
# 0003
operations = [
migrations.AddField(
model_name='authors',
name='project_data_set',
field=models.ManyToManyField(to='ticket_31788.ProjectDataSet'),
),
]
}}}
If you change the name of the field to something else like
`project_data_sets` every work as expected
{{{#!python
operations = [
migrations.AddField(
model_name='authors',
name='project_data_sets',
field=models.ManyToManyField(to='ticket_31788.ProjectDataSet'),
),
migrations.AlterUniqueTogether(
name='authors',
unique_together=set(),
),
migrations.RemoveField(
model_name='authors',
name='project_data_set',
),
]
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/31788#comment:4>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
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