I see two separate concerns here:
1) Should Django present to users the option to do validate-on-save by
default? That is, should that option be visible -- in the form of a
documented setting or an optional argument to save()?
I tend to accept James' (and others) views and reasoning against that.
2) Can a user activate validation-on-save-by-default without resorting
to monkeypatching? Should it be possible?
I think applying such validation should be possible -- because, in many
places, you see less-than-disciplined teams creating large projects
containing heaps of code that is not of the finest quality. And I think
we should help these projects improve incrementally -- that is,
introduce means to improve their situation; promoting notions like
data mutation should occur only in well-defined, controlled ways
without making them prerequisite.
This notion is a nice ideal, but installing it on a project
after-the-fact is hard; in many places it is not realistically
attainable -- at least in the boundaries of the team's resources,
delivery requirements, and a reasonable timeframe.
Note that for such general validation, a project-wide-base-model as
suggested e.g. by Uri is, in general, not sufficient, because it may
not apply to models from 3rd-party apps, or even from django.contrib
apps. Most models in such apps are not swappable.
But there is a way, I think, using a pre_save signal. One can write a
small app to install pre-save validation on all models in the project,
merely by including it in INSTALLED_APPS.
Basically,
from django.db.models import signals
...
class WhateverConfig(AppConfig):
...
def ready()
def validate(sender, instance, raw, **kwargs):
if not raw:
instance.full_clean()
signals.pre_save.connect(validate, weak=False)
This, of course, is just a POC -- it doesn't include things like
allowing a model to opt out, for example. Or one might want to apply it
only where settings.DEBUG is set. Or only log warnings. Or a few other
variations that don't jump to my mind immediately.
But it is a way for those of us involved with large teams and projects
to add this feature, without affecting the experience of newcomers or
the layer-separation sensibilities of the framework.
HTH,
Shai.
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