#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 | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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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.
--
Ticket URL: <https://code.djangoproject.com/ticket/31788>
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