Django adding CSS classes to field - django

Question

I am trying to add an error class to fields of a each form in a formset if a custom clean method detects errors. This does look to do the trick, I load the page, and the field does have the error class in it. but when in the template I add a custom filter to add a form-control class, everything falls apart.
# in my inlineformset:
def clean(self, *args, **kwargs):
if any(self.errors):
errors = self.errors
return
## 1) Total amount
total_amount = 0
for form in self.forms:
if self.can_delete and self._should_delete_form(form):
continue
amount = form.cleaned_data.get('amount')
total_amount += amount
if total_amount> 100:
for form in self.forms:
form.fields['amount'].widget.attrs.update({'class': 'error special'})
raise ValidationError(_('Total amount cannot exceed 100%'))
And, here is my code for the custom filter:
#register.filter(name = 'add_class')
def add_class(the_field, class_name):
''' Adds class_name to the string of space-separated CSS classes for this field'''
initial_class_names = the_field.css_classes() ## This returns empty string, but it should return 'error special'
class_names = initial_class_names + ' ' + class_name if initial_class_names else class_name
return the_field.as_widget(attrs = {'class': class_names,})
And, in my template:
{# {{ the_field|add_class:"form-control"}} #} #<- This adds the form-control, but removes the other classes added in the clean method
{{ the_field }} {# This shows the two classes for the offending fields, 'error special' #}
I think the problem is with the .css_classes() method which does not bring in the classes defined on the form. Remember, these classes have been set on these fields and rendering {{ the_field }} shows the classes were correctly passed down to the template. So, then the question is whether I am using the correct method .css_classes() or if I should use another method?

Answer 1

I was able to add class error to the field using .add_error method of the form. Although this works around the problem, I would still appreciate if anyone can explain how come the the_field.css_classes() returned an empty string instead of what was set in the clean method:
form.fields['amount'].widget.attrs.update({'class': 'error special'})
The problem with add_error method is that it only adds the class error. But, what if I'd want to add another class special to the widget? So, the original problem still needs an answer. My solution here then is just a solution and not the solution:
# in my inlineformset:
def clean(self, *args, **kwargs):
if any(self.errors):
errors = self.errors
return
## 1) Total amount
total_amount = 0
for form in self.forms:
if self.can_delete and self._should_delete_form(form):
continue
amount = form.cleaned_data.get('amount')
total_amount += amount
if total_amount > 100:
msg = 'This field throw the amount over the 100% limit'
form.add_error('amount', msg)
if total_amount> 100:
raise ValidationError(_('Total amount cannot exceed 100%'))