error_messages - Django Form Field Validation

Built-in Form Field Validations in Django Forms are the default validations that come predefined to all fields. Every field comes in with some built-in validations from Django validators. Each Field class constructor takes some fixed arguments. The error_messages argument lets you specify manual error messages for attributes of the field. The error_messages argument lets you override the default messages that the field will raise. Pass in a dictionary with keys matching the error messages you want to override. For example, here is the default error message:

>>> from django import forms
>>> generic = forms.CharField()
>>> generic.clean('')
Traceback (most recent call last):
  ...
ValidationError: ['This field is required.']

And here is a custom error message:

>>> name = forms.CharField(
                error_messages={
               'required': 'Please enter your name'
                })
>>> name.clean('')
Traceback (most recent call last):
  ...
ValidationError: ['Please enter your name']

Syntax

field_name = models.Field(option = value)

Django Form Field Validation error_messages Explanation

Illustration of error_messages using an Example. Consider a project named geeksforgeeks having an app named geeks.

Refer to the following articles to check how to create a project and an app in Django.

• How to Create a Basic Project using MVT in Django?
• How to Create an App in Django ?

Enter the following code into forms.py file of geeks app. We will be using CharField for experimenting for all field options. Python3

from django import forms

class GeeksForm(forms.Form):
    geeks_field = forms.CharField(
                  error_messages = {
                 'required':"Please Enter your Name"
                 })

Add the geeks app to INSTALLED_APPS Python3

# Application definition

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'geeks',
]

Now to render this form into a view we need a view and a URL mapped to that view. Let's create a view first in views.py of geeks app, Python3 1==

from django.shortcuts import render
from .forms import GeeksForm

# Create your views here.
def home_view(request):
    context = {}
    form = GeeksForm(request.POST or None)
    context['form'] = form
    if request.POST:
        if form.is_valid():
            temp = form.cleaned_data.get("geeks_field")
            print(temp)
    return render(request, "home.html", context)

Here we are importing that particular form from forms.py and creating an object of it in the view so that it can be rendered in a template. Now, to initiate a Django form you need to create home.html where one would be designing the stuff as they like. Let's create a form in home.html. html

<form method = "POST">
    {% csrf_token %}
    {{ form }}
    <input type = "submit" value = "Submit">
</form>

Finally, a URL to map to this view in urls.py Python3 1==

from django.urls import path

# importing views from views..py
from .views import home_view

URLpatterns = [
    path('', home_view ),
]

Let's run the server and check what has actually happened, Run

Python manage.py runserver

Now let's try to submit it empty and check if required error_message has been overridden. Thus the field is displaying a custom error message for required attribute of Charfield.

More Built-in Form Validations

Field Options	Description
required	By default, each Field class assumes the value is required, so to make it not required you need to set required=False
label	The label argument lets you specify the “human-friendly” label for this field. This is used when the Field is displayed in a Form.
label_suffix	The label_suffix argument lets you override the form’s label_suffix on a per-field basis.
widget	The widget argument lets you specify a Widget class to use when rendering this Field. See Widgets for more information.
help_text	The help_text argument lets you specify descriptive text for this Field. If you provide help_text, it will be displayed next to the Field when the Field is rendered by one of the convenience Form methods.
error_messages	The error_messages argument lets you override the default messages that the field will raise. Pass in a dictionary with keys matching the error messages you want to override.
validators	The validators argument lets you provide a list of validation functions for this field.
localize	The localize argument enables the localization of form data input, as well as the rendered output.
disabled.	The disabled boolean argument, when set to True, disables a form field using the disabled HTML attribute so that it won’t be editable by users.