基于同一模型中其他字段的Django字段验证器

Question

I have this model

class Env(models.Model):    
    functional_count = models.PositiveIntegerField()    
    current_count = models.PositiveIntegerField()

Now i want functional_count to always be less than current_count .
So during create,

def form_valid(self, form):    
    form.instance.current_count = 0

This is because i want current_count during initialization.Then my python code never allows current_count to go above functional_count .

The problem comes in Update.

class EnvUpdate(UpdateView):  
    model = Capacity.models.Envapps  
    fields = ['functional_count']  
    template_name_suffix = '_update_form'

So do i include a validator? If yes, where and how?
Or other option is to verify in get_success_url() .
Any other solution?

Answer 1

Assuming your updates come through a form (as suggested by the use of form_valid() , perhaps you can use the form clean() method, as described in the documentation . This allows you to perform checks for fields that depend on each other. The documentation also has an example which should get you further.

Update

From your comments, I understand that you tried to use clean() inside EnvUpdate , which inherits from the class-based UpdateView view. All the mixins provided through UpdateView do apparently not provide a clean() method, so you can't override it.

I am actually referring to the clean() in a form class (as follows from the link). So, it looks like you'd need to create your own ModelForm class, something like:

class EnvappsForm(forms.ModelForm):
    class Meta:
        model = Capacity.models.Envapps
        fields = ['functional_count']

    def clean(self):
       cleaned_data = super(ContactForm, self).clean()
       if cleaned_data['functional_count'] >= form.instance.current_count:
           raise ValidationError('too large')
       return cleaned_data

and then in your view:

class EnvUpdate(UpdateView):
    model = Capacity.models.Envapps  
    template_name_suffix = '_update_form'
    form_class = EnvappsForm

Note: this is completely untested! I don't know if the comparison in the clean() works (ie, if form.instance.current_count can be found), and wheter EnvUpdate will override the form_class (it shouldn't, but I've never tried). It just might be even possible that you can remove the meta subclass, and provide the model and fields from EnvUpdate , as you do yourself above. That's just something you can easily try out.

Answer 2

If functional_count should always be less than current_count you should check it in the clean() method on the model and not some random ModelForm . The model clean() will be called during normal ModelForm validation.