Hi Simon,
Thanks! Using an ExpressionWrapper does work for this :)
I agree it might be nice to have a bit less boilerplate here. What I'd
first tried was actually:
```
CheckConstraint(check=Q(
is_on_sale=F('price') < F('full_price'),
))
```
It would be great if that could be made to work -
Hi All,
Let try sth like sample:
a = True if b <= c else False
On Tue, Jan 28, 2020, 03:24 Simon Charette wrote:
> I see, I think you'll need to wrap the inner Q in an ExpressionWrapper[0]
>
> That would be
>
> CheckConstraint(check=Q(is_on_sale=ExpressionWrapper(Q(price__lt=F('full_price')),
I see, I think you'll need to wrap the inner Q in an ExpressionWrapper[0]
That would be
CheckConstraint(check=Q(is_on_sale=ExpressionWrapper(Q(price__lt=F('full_price')),
output_field=models.BooleanField(
That involves a lot of boilerplate though and it ought to work without all
of it so
Hi Simon,
Thanks for your response.
I did try that, however unfortunately I get an error when running the
migration:
django.core.exceptions.ValidationError: ["'(AND:
)' value must
be either True or False."]
I'm using Django 2.2 LTS though testing this in 3.0 unfortunately errors in
the same
Hi Stephen,
Thanks for your response.
I agree that using an annotation might be an alternative way to solve this,
however for various reasons that's not suitable for my current use case. I
was also hoping for a general solution which would work for cases where the
expression is more complicate
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
sorry i diin't read to Stephen his trik is even better hahahaha but with
sigñal yo ca do other thing
El lun., 27 ene. 2020 a las 19:02, DANIEL URBANO DE LA RUA (<
dannybombas...@gmail.com>) escribió:
> you can do few thing at the same time in a model before save or whenever
> you want
>
> El lun.
you can do few thing at the same time in a model before save or whenever
you want
El lun., 27 ene. 2020 a las 19:01, DANIEL URBANO DE LA RUA (<
dannybombas...@gmail.com>) escribió:
> it is goin to be better and less cost for the db
>
> El lun., 27 ene. 2020 a las 19:01, DANIEL URBANO DE LA RUA (<
take a look at this https://docs.djangoproject.com/en/3.0/topics/signals/
El lun., 27 ene. 2020 a las 18:59, Stephen J. Butler (<
stephen.but...@gmail.com>) escribió:
> Frankly, if is_on_sale has such a tight constraint I wouldn't have it as
> its own column. Why not just make it an annotated fi
it is goin to be better and less cost for the db
El lun., 27 ene. 2020 a las 19:01, DANIEL URBANO DE LA RUA (<
dannybombas...@gmail.com>) escribió:
> take a look at this https://docs.djangoproject.com/en/3.0/topics/signals/
>
>
> El lun., 27 ene. 2020 a las 18:59, Stephen J. Butler (<
> stephen.b
Frankly, if is_on_sale has such a tight constraint I wouldn't have it as
its own column. Why not just make it an annotated field with an F
expression?
https://docs.djangoproject.com/en/3.0/ref/models/expressions/#using-f-with-annotations
Item.objects.annotate(is_on_sale=(F('price') < F('full_pric
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 fi
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