Models migration with change field foreign to many and deleting unique together.

[budzichd]

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.

[budzichd]

Download this file and then do makemigrations and migrate to see this error.