Did you try
class Item(Model):
price = DecimalField()
full_price = DecimalField()
is_on_sale = BooleanField()
class Meta:
constraints = [
CheckConstraint(check=Q(is_on_sale=Q(price__lt=F('full_price'))))
]
I haven't tried it myself but I would expect it to work on Django 3.0.
Cheers,
Simon
Le lundi 27 janvier 2020 12:47:37 UTC-5, Peter Law a écrit :
>
> Hi,
>
> Thanks for adding support for check constraints in Django 2.2, it's
> great to be able to move constraints into the model definitions.
>
> I've been trying to work out how to express a constraint which
> validates that the value of one field expresses a relation between two
> other fields, but can't find a nice way to do so.
>
> I've read through the docs and also found
> https://groups.google.com/d/topic/django-users/6Olh5V1b7Us/discussion,
> but haven't found a concise spelling.
>
> I've got a model like:
>
> ```
> class Item(Model):
> price = DecimalField()
> full_price = DecimalField()
> is_on_sale = BooleanField()
> ```
>
> I'd like to be able to express neatly that the `is_on_sale` boolean be
> true only when `price < full_price`.
> In Postgres I can express this as:
>
> ```
> ALTER TABLE item
> ADD CONSTRAINT is_on_sale_check
> CHECK (is_on_sale = (price < full_price))
> ```
>
> However in Django I can't find a way to express this directly.
>
> I did find a long spelling which essentially checks the True case and
> the False case explicitly and then ORs them together, however it's
> several lines of `models.Q` combinations and not at all clear about
> what the code is trying to achieve.
>
> Is there a concise way to do this sort of constraint? If not, would it
> be possible for Django to add support for it?
>
> Thanks,
> Peter
>
--
You received this message because you are subscribed to the Google Groups
"Django users" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to django-users+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-users/93fe186a-4f25-4ec2-ac5c-f28fd882812f%40googlegroups.com.
