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Description:

djangodeprecation 0.1.1

django-deprecation

Deprecate django fields and make migrations without breaking existing code.
Install
pip install django-deprecation

Usage
TL;DR
# Before:
class Album(models.Model):
name = models.CharField(max_length=50)

# After:
class Album(models.Model):
name = DeprecatedField('title')
title = models.CharField(max_length=50)

assert album.name == album.title
assert list(Album.objects.filter(name='foo')) == list(Album.objects.filter(title='foo'))

Long explanation
Let's suppose we have the following models:
from django.db import models

class Musician(models.Model):
name = models.CharField(max_length=50)

class Album(models.Model):
musician = models.ForeignKey(Musician, on_delete=models.CASCADE)
name = models.CharField(max_length=100)

Now, for some reason, let's suppose we want to rename the field Album#musician to Album#artist.
So we make the migration using the
RenameField
operation. The problem is that any existing code that used the old field would break.
We could create a property as an alias:
class Album(models.Model):
artist = models.ForeignKey(Musician, on_delete=models.CASCADE)
name = models.CharField(max_length=100)

@property
def musician(self):
return self.artist

@musician.setter
def musician(self, value):
self.artist = value

But any code using
QuerySet#filter
would break if it uses the musician field.
This is where django-deprecation comes handy.
We set the musician field as a DeprecatedField and point it to the artist field:
from django_deprecation import DeprecatedField

class Album(models.Model):
artist = models.ForeignKey(Musician, on_delete=models.CASCADE)
musician = DeprecatedField('artist')
name = models.CharField(max_length=100)

Now, the following code snippet will work:
from .models import Album, Musician

album = Album.objects.first()
assert album.musician == album.artist

new_musician = Musician.objects.create(
first_name='John',
last_name='Doe',
instrument='Guitar',
)
album.musician = new_musician
assert album.artist == new_musician

new_musician_album = Album.objects.filter(
musician=new_musician,
).first()
new_artist_album = Album.objects.filter(
artist=new_musician,
).first()
assert new_musician_album == new_artist_album

If you want to control how to report the error,
replace the DeprecatedField.warn function with a custom one:
from django_deprecation import DeprecatedField

def warn_function(message):
# do stuff
import warnings
warnings.warn(message, DeprecationWarning)

DeprecatedField.warn = warn_function