How to send additional data to the template when Django ValidationError occurred on a specific field?

Question

Let us say, I have a Django Form - XYZ which had fields A, B, C. Field B is username field, when a particular username already exists, Validation Error occurs and throws back a message. Along with that I want to send some auto-suggested username-dict to the template. As per my understanding, i can only send as Field Errors and Non-Field errors.

def clean_B(self):
        B = self.cleaned_data['B']
        if address.objects.filter(B=B).exists():
            raise forms.ValidationError("Username already exists")
        return B

I tried to add another error using Form.add_error() and Django doesn't allow multiple errors in a single dict per field or Non_field errors.

How can i do this?

Thanks!

Answer 1

I think you can use django messages framework to show your message with suggestions to user.

from django.contrib import messages

...

def clean_B(self):
    B = self.cleaned_data['B']
    if address.objects.filter(B=B).exists():
        # In __init__ method of the form, you should store request as property
        messages.info(self.request, 'You should use another username, i.e. John')
        raise forms.ValidationError('Username already exists')
    return B

And then, somewhere in your template, output message:

{% if messages %}
<ul class="messages">
    {% for message in messages %}
    <li{% if message.tags %} class="{{ message.tags }}"{% endif %}>{{ message }}</li>
    {% endfor %}
</ul>
{% endif %}