django alter form data in clean method

I have a django form that I want to custom clean. Instead of just specifying an error message like here (Django form and field validation), I'd like to just alter the field myself. I tried severl ways, but keep running into error like cleaned_data is immutable.

So to solve this I made a copy, changed it and reassigned it to self. Is this the best way to do this? Could/should I have handled this in the view? Making a copy seems poor form but I keep running into 'immutabl开发者_运维技巧e' road blocks. Sample code below where I simply check if the subject has '--help' at the end, and if not add it. Thanks

def clean(self):
        cleaned_data=self.cleaned_data.copy()
        subject=cleaned_data.get['subject']
        if not subject.endswith('--help'):
            cleaned_data['subject']=subject+='--help'
        self.cleaned_data=cleaned_data
        return self.cleaned_data

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The correct way to deal with this is by using the field specific clean methods.

Whatever you return from the clean_FOO method is what the cleaned_data will be populated with by the time it gets to the clean function.

Do the following instead:

def clean_subject(self):
        data = self.cleaned_data.get('subject', '')
        if not data:
             raise forms.ValidationError("You must enter a subject")
             # if you don't want this functionality, just remove it.

        if not data.endswith('--help'):
             return data += '--help'
        return data

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I think your problem is that you have called self.cleaned_data.get['subject'], and then used it as an array later on.

I have this code for a messaging app that replaces an empty subject with 'No Subject'

def clean(self):
    super(forms.ModelForm, self).clean()
    subject = self.cleaned_data['subject']
    if subject.isspace():
        self.cleaned_data['subject'] = 'No Subject'
    return self.cleaned_data

For your code, this should work.

def clean(self):
    super(forms.Form, self).clean() #I would always do this for forms.
    subject = self.cleaned_data['subject']
    if not subject.endswith('--help'):
        subject += '--help'
        self.cleaned_data['subject'] = subject
    return self.cleaned_data

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So, I found this recently having googled about possibly the same problem, whereby in a ModelForm instance of a form, I was trying to edit the data post-validation to provide a suggestion for the end user as to something that would be a valid response (computed from another value they enter into the form).

TL;DR

If you are dealing with a ModelForm descendent specifically, there are two things that are important:

1. You must call super(YourModelFormClass, self).clean() so that unique fields are checked.

2. If you are editing cleaned_data, you must also edit the same field on the instance of your model which is attached to your ModelForm:

   def clean(self)
     self.cleaned_data = super(MyModelFormClass, self).clean()
     self.cleaned_data['name']='My suggested value'
     self.instance.name = 'My suggested value'
     return self.cleaned_data
   

Documentation source for this behaviour

EDIT:

Contrary to the documentation, I have just found that this does not work. you have to edit the form's self.data in order to get the changes to show up when the form displays.

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"This method should return the cleaned value obtained from cleaned_data, regardless of whether it changed anything or not." from https://docs.djangoproject.com/en/dev/ref/forms/validation/