Create Custom Error Messages with Model Forms - django

Question

I can see how to add an error message to a field when using forms, but what about model form?
This is my test model:
class Author(models.Model):
first_name = models.CharField(max_length=125)
last_name = models.CharField(max_length=125)
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
My model form:
class AuthorForm(forms.ModelForm):
class Meta:
model = Author
The error message on the fields: first_name and last_name is:
This field is required
How do I change that in a model form?

Answer 1

For simple cases, you can specify custom error messages
class AuthorForm(forms.ModelForm):
first_name = forms.CharField(error_messages={'required': 'Please let us know what to call you!'})
class Meta:
model = Author

Answer 2

New in Django 1.6:
ModelForm accepts several new Meta options.
Fields included in the localized_fields list will be localized (by setting localize on the form field).
The labels, help_texts and error_messages options may be used to customize the default fields, see Overriding the default fields for details.
From that:
class AuthorForm(ModelForm):
class Meta:
model = Author
fields = ('name', 'title', 'birth_date')
labels = {
'name': _('Writer'),
}
help_texts = {
'name': _('Some useful help text.'),
}
error_messages = {
'name': {
'max_length': _("This writer's name is too long."),
},
}
Related: Django's ModelForm - where is the list of Meta options?

Answer 3

Another easy way of doing this is just override it in init.
class AuthorForm(forms.ModelForm):
class Meta:
model = Author
def __init__(self, *args, **kwargs):
super(AuthorForm, self).__init__(*args, **kwargs)
# add custom error messages
self.fields['name'].error_messages.update({
'required': 'Please let us know what to call you!',
})

Answer 4

I have wondered about this many times as well. That's why I finally wrote a small extension to the ModelForm class, which allows me to set arbitrary field attributes - including the error messages - via the Meta class. The code and explanation can be found here: http://blog.brendel.com/2012/01/django-modelforms-setting-any-field.html
You will be able to do things like this:
class AuthorForm(ExtendedMetaModelForm):
class Meta:
model = Author
field_args = {
"first_name" : {
"error_messages" : {
"required" : "Please let us know what to call you!"
}
}
}
I think that's what you are looking for, right?

Answer 5

the easyest way is to override the clean method:
class AuthorForm(forms.ModelForm):
class Meta:
model = Author
def clean(self):
if self.cleaned_data.get('name')=="":
raise forms.ValidationError('No name!')
return self.cleaned_data

Answer 6

I have a cleaner solution, based on jamesmfriedman's answer.
This solution is even more DRY, especially if you have lots of fields.
custom_errors = {
'required': 'Your custom error message'
}
class AuthorForm(forms.ModelForm):
class Meta:
model = Author
def __init__(self, *args, **kwargs):
super(AuthorForm, self).__init__(*args, **kwargs)
for field in self.fields:
self.fields[field].error_messages = custom_errors

Answer 7

You can easily check and put custom error message by overriding clean()method and using self.add_error(field, message):
def clean(self):
super(PromotionForm, self).clean()
error_message = ''
field = ''
# reusable check
if self.cleaned_data['reusable'] == 0:
error_message = 'reusable should not be zero'
field = 'reusable'
self.add_error(field, error_message)
raise ValidationError(error_message)
return self.cleaned_data