Question

I have the following models (simplified):

class Location(models.Model):
    name = models.CharField(max_length=100)
    is_ok = models.BooleanField()

class Profile(models.Model):
    name = models.CharField(max_length=100)
    location = models.ForeignKey(Location)

class AnotherThing(models.Model):
    name = models.CharField(max_length=100)
    location = models.ForeignKey(Location)

I use a modelform to allow the users to add/edit Profile and AnotherThing items in the database.
Simplified version:

class ProfileForm(ModelForm):
    class Meta:
        model = Profile
        widgets = {'location': CustomLocationWidget()}

class AnotherThingForm(ModelForm):
    class Meta:
        model = Profile
        widgets = {'location': CustomLocationWidget()}

The simplified code for CustomLocationWidget is something like this:

class CustomLocationWidget(Input):
    def __init__(self, *args, **kwargs):
        super(CustomLocationWidget, self).__init__(*args, **kwargs)

    def render(self, name, value, attrs = None):
        output = super(CustomLocationWidget).render(name, value, attrs)
        output += 'Hello there!'
        return mark_safe(output)

As another validation I need to check that the Location has is_ok == True before saving. I can easily do this in the ModelForm for each item but the code is identical in each case and breaks DRY. How can I add it to each form without writing the code for it twice? Is it possible to attach the validator to the widget?

I was looking at default_validators but I don’t know what other validators are used for ForeignKey fields and how to actually declare the validator.

Answer 1

Validation lives on fields, not widgets. If you need the same custom validation in a bunch of forms, define a custom field, add a clean method to that field containing that validation code, then define the field’s widget attribute to be your custom widget. Then you can simply reference that field in any of your forms.