Create Custom Error Messages with Model Forms

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?

davelupt · Accepted Answer · 2015-08-18 20:31:35Z

62

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

edited Aug 18, 2015 at 20:31

davelupt

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answered Aug 9, 2010 at 3:29

chefsmart

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4 Comments

iJK Over a year ago

Cool thanks. I did not know what would be the result of doing that. The documentation says "Declared fields will override the default ones generated by using the model attribute" so I should be good. I would also have to set the max_field again on the model form field.

paweloque Over a year ago

Is it really necessary to repeat field declarations in the form? How about the DRY principle django is proud of?

Denis Over a year ago

LOL, man, I think OP want use forms from models but not declare forms two times.

gabn88 Over a year ago

I think that with respect to the client side, being explicit is more important then DRY.

Community · Accepted Answer · 2017-05-23 12:02:41Z

59

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?

edited May 23, 2017 at 12:02

CommunityBot

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answered Feb 13, 2014 at 18:44

doctaphred

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6 Comments

Eric S. Over a year ago

i don't understand the _() surrounding the custom error message text, so i took that out. but this is the first snippet that worked for me. i'm on django 1.6. thank you, sir!

doctaphred Over a year ago

You're welcome! If you're curious, the underscore function is a common shortcut for an internationalization utility: stackoverflow.com/questions/2964244/…

mrchestnut Over a year ago

I think this should be the accepted answer as it follow DRY principles. When using ModelForm, there shouldn't be a need to declare fields again and there shouldn't be a need to override methods either.

Uri Over a year ago

The defaults in the Meta class are only used if the fields and widgets are not defined deliberately. If they are defined deliberately, the error messages should be defined there, or in the __init__ method.

Uri Over a year ago

stackoverflow.com/questions/57424228/…

|

slajma · Accepted Answer · 2020-01-15 03:47:44Z

21

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!',
        })

edited Jan 15, 2020 at 3:47

slajma

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answered Mar 27, 2013 at 3:11

jamesmfriedman

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2 Comments

Vladimir Prudnikov Over a year ago

This is much better solution than all other in this thread because 1) You don't have to use any extensions 2) you don't have to rewrite whole form field definition because it depends on definition of model field. +1

Vladimir Prudnikov Over a year ago

One note thought, you have to use it like this self.fields['name'].error_messages['required'] = 'Please let us know what to call you!' or using .update() method, otherwise you reset all other error messages.

jbrendel · Accepted Answer · 2012-01-23 19:11:30Z

15

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?

answered Jan 23, 2012 at 19:11

jbrendel

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2 Comments

suda Over a year ago

This is a great way to do this. Certainly more DRY than redefining form fields.

Chris Over a year ago

@suda you aren't really redefining, you are overriding the default behavior based on the model associated. similar to changing an input to a textarea, you are overriding the default.

Mermoz · Accepted Answer · 2010-08-09 01:11:53Z

7

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

answered Aug 9, 2010 at 1:11

Mermoz

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Comments

Vingtoft · Accepted Answer · 2015-02-17 19:54:28Z

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

answered Feb 17, 2015 at 19:54

Vingtoft

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1 Comment

Harlin Feb 25 at 18:40

Exactly what I was looking for. This is the right way to do it.

Moe Far · Accepted Answer · 2017-05-31 09:56:27Z

4

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

answered May 31, 2017 at 9:56

Moe Far

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