import sys
import warnings
from django.db.models import BooleanField, NullBooleanField
class DeprecatedField(object):
"""
Descriptor class for deprecated fields. Do not use directly, use the
deprecate_field function instead.
"""
def __init__(self, val):
self.val = val
def _get_name(self, obj):
"""
Try to find this field's name in the model class
"""
for k, v in type(obj).__dict__.items():
if v is self:
return k
return '<unknown>'
def __get__(self, obj, type=None):
warnings.warn('accessing deprecated field %s.%s' % (
obj.__class__.__name__, self._get_name(obj)
), DeprecationWarning, stacklevel=2)
if not callable(self.val):
return self.val
return self.val()
def __set__(self, obj, val):
warnings.warn('writing to deprecated field %s.%s' % (
obj.__class__.__name__, self._get_name(obj)
), DeprecationWarning, stacklevel=2)
self.val = val
def deprecate_field(field_instance, return_instead=None):
"""
Can be used in models to delete a Field in a Backwards compatible manner.
The process for deleting old model Fields is:
1. Mark a field as deprecated by wrapping the field with this function
2. Wait until (1) is deployed to every relevant server/branch
3. Delete the field from the model.
For (1) and (3) you need to run ./manage.py makemigrations:
:param field_instance: The field to deprecate
:param return_instead: A value or function that
the field will pretend to have
"""
if not set(sys.argv) & {"makemigrations", "migrate", "showmigrations"}:
return DeprecatedField(return_instead)
if not type(field_instance) == BooleanField:
field_instance.null = True
return field_instance
# A BooleanField does not allow null=True, so we need to cast
# this to a NullBooleanField
return NullBooleanField(
help_text=field_instance.help_text,
default=field_instance.default
)
