#23861: IPAddressField removal will break migrations and test suites
-----------------------------+--------------------------------------
Reporter: spookylukey | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: master
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-----------------------------+--------------------------------------
Changes (by MarkusH):
* cc: info+coding@… (added)
Comment:
A few thoughts I collected over the last days while silently following the
discussion here:
- We should extend the lifetime of removed fields by a single version as
stub fields. Shouldn't be too hard to get something "working" in
migrations (aka not failing) but throwing warnings or blowing up during
normal use.
- Magic that happens during migrations and adds some legacy fields back,
but not during "normal" runtime, makes migrations even worse to debug.
It's hard enough to figure out where and when (in which migration) a model
was defined.
- The problem Django has with the `IPAddressField` is kind of a luxury. We
could add some magic that will make migrations work even after the field
was removed. This won't work for 3rd party apps though (as already said).
Thus magic import features, as stated above, shouldn't be a solution.
- Carl's idea to make `operations` a property that internally imports all
used code, could work. I'm not sure what we are missing though.
- Going with some `@lazy` decorator or implementation won't help in any
way. The classes still need to be imported.
- Referencing imports by strings would be possible, but it's quite
invasive:
{{{#!python
from django.db import migrations, get_migration_operation,
get_migration_thing
def get_migration_operation(to_import, *args, **kwargs):
try:
klass = import_string(to_import)
return klass(*args, **kwargs)
except ImportError:
return NoOp()
def get_migration_thing(to_import, *args, **kwargs):
try:
klass = import_string(to_import)
return klass(*args, **kwargs)
except ImportError:
# raise warning / error
class Migration(migrations.Migration):
dependencies = []
operations = [
migrations.get_migration_operation('django.db.migrations.operations.CreateModel',
fields=[
migrations.get_migration_thing('myapp.fields.MyField', 'x',
'y'),
]),
migrations.get_migration_operation('django.db.migrations.operations.ANewOperationIn18',
'arg1', kwarg1='kwarg1'),
]
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/23861#comment:10>
Django <https://code.djangoproject.com/>
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