I have an issue with migrations.
Suppose I declare (in my application, with name myapp) a field with a
validators= declared. In such value (which is an iterable), I declare a
function:
class MyModel(models.Model):
"""
This one is identifiable.
"""
identifier = models.CharField(max_length=10, unique=True, validators=[
valid_identifier])
Assume I created the migration with makemigrations:
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import models, migrations
from django.conf import settings
import django.core.validators
import micnt.models
class Migration(migrations.Migration):
dependencies = [
...
]
operations = [
migrations.CreateModel(
name='MyModel',
fields=[
('identifier', models.CharField(max_length=10, unique=True,
validators=[myapp.models.valid_identifier])),
],
options={
},
bases=(models.Model,),
),
]
Assume valid_identifier is any external callable which will take one
positional argument, and eventually raise ValidationError under certain
conditions.
Now the requirements vary: The identifier may be national or foreign, so
the country is required as an additional field, and also a discriminator
field. Additionally, the validation I must perform is cross-field, so
instead of using something in validators, I define a clean() method, and
make the combination of country/identifier unique, instead of just the
identifier unique:
class MyModel(models.Model):
"""
This one is identifiable.
"""
identifier_type = models.CharField(max_length=10, choices=(('passport',
_(u'Passport')), ('national', _(u'National'))), null=False)
identifier = models.CharField(max_length=10)
country = models.ForeignKey(Country, null=False) # assume Country
model exists
class Meta:
unique_together = (('identifier', 'country'),)
def clean(self):
raise ValidationError('Implement this!')
And then, I don't need anymore the valid_identifier function, since my code
does not use it anymore. So I delete it.
Now I will create the migration with makemigrations as usual. What will
happen?
a. The command will succeed.
b. The command will explode (i. e. a normal Python exception).
c. The command will create an inconsistent migration, without exploding.
d. Jesus will come again.
e. The command will get into a kind of endless loop.
If you guesses "b", you were right. Django will report an error, since
myapp.models.valid_identifier does not exist anymore (AttributeError).
So, once I set a value for validators= parameter and create a migration, I
am forced to keep such reference valid for the rest of my life (e.g. by
having valid_identifier=None, if I don't need the function anymore), or
else the migrations will not work again since they will be traversed,
imported, and will get such AttributeError.
Is this an expected, normal, behavior?
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