Hi Django Developers,
I'm new to contributing and from what I gathered, I should ask here before
opening a ticket.
Right now the way to validate a model as a whole is to override
Model.clean(). I have 2 problems with this:
1) If you do multiple checks that raise ValidationErrors, it is tedious to
accumulate them.
2) Having different models that checks almost the same, e.g. start_date
should come before end_date, it should be easy to reuse validators.
I suggest to add a 'validators' option to Model Meta options.
This should be very similar to the 'validators' option a Field has, a list
of callables that raises ValidationErrors, except these should take an
object 'instance' instead of a 'value'.
It should then be Model.full_clean() responsibility to call these model
validators in addition to what it already does.
A concern I have is the confusion that may rise between these new 'model
validators' and regular 'field validators'. Maybe clever naming could help
distinguish them from eachother, and maybe it's not a huge deal since they
are so closely related.
It would be nice if some common model validators got built-in as well. For
example a ComparisonModelValidator could take the names of two fields and
validate if they are in the right order, it could look like
class ComparisonModelValidator(low, high, message=None, code=None)
* low - field name of the lesser field
* high - field name of the greater field
* message - if not None, overrides message
* code - if not None, overrides code
Then it could be used in the model as
class Event(models.Model):
start_date = models.DateField()
end_date = models.DateField()
...
class Meta:
validators = [ComparisonModelValidator('start_date', 'end_date')]
All feedback is appreciated.
Mathias
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