Question

The 2 types of validation error a form field in django can have are ‘required’ and ‘invalid’. Is there any way to find out which of these two errors has happened, from the template? Something like

{% if form.username.errors %}
{% for error in form.username.errors %}
{% if error.required %}
Please enter the username
{% else %}
{{ error }}
{% endif %}

I just want to override the error message for the ‘required’ error, i.e., I want to display my own error message if that error happens. I am using django.contrib.auth.views which uses django.contrib.auth.forms.AuthenticationForm which I don’t want to try customizing.

Answer 1

You really should just override the Authentication form. The view accepts an argument that allows for you to override form easily.

I think something like this should work:

All you need to do is override the clean_username method like so:
edit:

overriding the clean_username method fails to change the validation error message because of the following from the form and field validation docs:

• The clean() method on a Field
  subclass. This is responsible for
  running to_python, validate and
  run_validators in the correct order
  and propagating their errors. If, at
  any time, any of the methods raise
  ValidationError, the validation stops
  and that error is raised. This method
  returns the clean data, which is then
  inserted into the cleaned_data
  dictionary of the form.

• The clean_<fieldname>() method in a
  form subclass – where is
  replaced with the name of the form
  field attribute. This method does any
  cleaning that is specific to that
  particular attribute, unrelated to the
  type of field that it is. This method
  is not passed any parameters. You will
  need to look up the value of the field
  in self.cleaned_data and remember that
  it will be a Python object at this
  point, not the original string
  submitted in the form (it will be in
  cleaned_data because the general field
  clean() method, above, has already
  cleaned the data once).

The Field subclass is validated first and returns the cleaned data that is used for the clean_<field_name>() method. If an error occurs there the validation of that field stops.

This means that to override the message you need to either override the Field validation or make the field not require a value so no validation error is raised at that step and raise a required method in the clean_<fieldname>() method

>>> from django.contrib.auth.forms import AuthenticationForm
>>> class MyAuthForm(AuthenticationForm):
...     def __init__(self, *args, **kwargs):
...         super(MyAuthForm, self).__init__(*args,**kwargs)
...         self.fields['username'].error_messages['required']='Custom Required Msg'
... 
>>> form = MyAuthForm(data={'password':'asdf'})
>>> form.is_valid()
False
>>> form.errors
{'username': [u'Custom Required Msg']}
>>> 

urls.py

from someapp.forms import MyAuthForm

urlpatterns = patterns('',
    ...
    (r'^accounts/login/$', 'django.contrib.auth.views.login', {'template_name': 'someapp/login.html', 'authentication_form':MyAuthForm, }),
    ...