Django Forms | Custom Form Validations

In this post we’ll learn to create user-defined functions, displaying validation errors in the template for Django Form Validations.

Table Of Contents

Introduction

The forms are a Django Module which deals with all form-related functions from binding POST data to form, Validating form and rendering HTML field in the template.
We’ll be using below models.py file as an example to demonstrate form validations.

from django.db import models
from django.contrib.auth.models import User
from datetime import datetime

class AuthUserProfile(models.Model):
    user_profile_id = models.AutoField(primary_key=True)
    user = models.OneToOneField(User, on_delete=models.CASCADE, related_name='auth_user_profile')
    dob =  models.DateField(blank=True, null=True)
    is_deleted = models.PositiveSmallIntegerField(default=0)
    created_at = models.DateTimeField(auto_now=datetime.now(), null=True)
    updated_at = models.DateTimeField(auto_now=datetime.now(), null=True)

    class Meta():
        db_table = 'auth_user_profile'
        verbose_name = 'User Profile'
        verbose_name_plural = 'User Profiles'

    def __str__(self):
        return self.user

Create a form which has these fields (first_name, last_name, username, password, email) from User models and field (dob) in AuthUserProfile Model and also will add custom field and non-field level validation.

Creating Form

In forms.py file import forms from Django. Inherit forms.Form to UserForm and add attributes to the field.

from django import forms
from datetime import datetime
from django.contrib.auth.models import User

class UserForm(forms.Form):
    first_name = forms.CharField(label="First Name*",widget=forms.TextInput(attrs={'required':True,'class':"form-control"}))
    last_name = forms.CharField(label="Last Name*",widget=forms.TextInput(attrs={'required':True,'class':"form-control"}))
    username = forms.CharField(label="User Name*",widget=forms.TextInput(attrs={'required':True,'class':"form-control"}))
    email = forms.CharField(label="Email",widget=forms.TextInput(attrs={'type':'email','required':False,'class':"form-control"}))
    date_of_birth = forms.CharField(label="Date of Birth",widget=forms.TextInput(attrs={'type':'date','required':True,'class':"form-control"}))
    password = forms.CharField(label="Password*",widget=forms.TextInput(attrs={'required':True,'class':"form-control", 'type' : "password"}))
    confirm_password = forms.CharField(label="Confirm Password*",widget=forms.TextInput(attrs={'required':True,'class':"form-control", 'type' : "password"}))
    
    def clean(self):
        # user age must be above 18 to register
        if self.cleaned_data.get('date_of_birth'):
            dob = datetime.strptime(self.cleaned_data.get('date_of_birth'),"%Y-%m-%d")
            now = datetime.now()
            diff = now.year-dob.year

            if diff < 18: msg="User must be atleast 18 years old" self.add_error(None, msg) #check if user name is unique username_count = User.objects.filter(username=self.cleaned_data.get('username')).count() if username_count>0:
            msg="Username '{}' has already been used.".format(self.cleaned_data.get('username'))
            self.add_error(None, msg)
        
    def clean_confirm_password(self):
        password = self.cleaned_data.get('password')
        confirm_password = self.cleaned_data.get('confirm_password')
        if confirm_password!=password:
            msg = "Password and Confirm Passwords must match."
            self.add_error('confirm_password', msg)

You may notice clean() and clean_confirm_password() methods in UserForm the form they are validation methods.
The clean() the method is form level validation this can also be used to perform field-level validation.

And the clean_confirm_password() is a field-level validation for confirm_password the field it checks if confirm_password!=password then adds error to a then particular field.

Rendering Form

Rendering of forms is an easy part we must pass the form object as an argument to render function.

In views.py create a function user_profile_create which will display rendered form.

from django.contrib.auth.models import User
from users.models import AuthUserProfile
from forms.forms import UserForm
from django.contrib.auth.hashers import make_password
from django.contrib import messages

def user_profile_create(request):
    form = UserForm()
    template="forms/user_profile_create_form.html"
    return render(request,template,{"form":form})

form = UserForm() creates form object of UserForm and is passed as an argument to the render() function.

In urls.py file add routes to view.

urlpatterns = [
    path('user/profile/create', views.user_profile_create, name='user-profile-create'),
]

Create an HTML file in your apps template folder naming user_profile_create_form.html.

<!DOCTYPE html>
<html lang="en">            
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Django Form Validation</title>
        <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.0/css/bootstrap.min.css">
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
        <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.0/js/bootstrap.min.js"></script>
        <style>
            .error{
                color:red;
            }
        </style>
    </head>            
    <body>
        <div class="container">
        
            {% if messages %}
                {% for message in messages %}
                    {% if message.level == DEFAULT_MESSAGE_LEVELS.SUCCESS %}
                    <div class="alert alert-success"
                    role="alert">
                        <div id="primary-notification-div">
                            {{ message }}
                        </div>
                    </div>
                    {% endif %}
                {% endfor %}
            {% endif %}
                
            <h1>User Profile</h1>
            <form action="{% url 'forms:user-profile-save' %}" method="post">
                {% csrf_token %}
    
                {% if form.errors %}
                    {% for error in form.non_field_errors %}
                        <div class="alert alert-danger">
                            <strong>{{ error|escape }}</strong>
                        </div>
                    {% endfor %}
    
                {% endif %}
    
    
                <div class="row">
                    <div class="col-md-3">
                        {{form.first_name.label}}
                        {{form.first_name}}
    
                        {% if form.errors.first_name %}
                            <label for="" class="error">{{form.errors.first_name|striptags}}</label>
                        {% endif %}
                    </div>
    
                    <div class="col-md-3">
                        {{form.last_name.label}}
                        {{form.last_name}}
                        {% if form.errors.last_name %}
                            <label for="" class="error">{{form.errors.last_name|striptags}}</label>
                        {% endif %}
                    </div>
    
                    <div class="col-md-3">
                        {{form.username.label}}
                        {{form.username}}
                        {% if form.errors.username %}
                            <label for="" class="error">{{form.errors.username|striptags}}</label>
                        {% endif %}
                    </div>
    
                    <div class="col-md-3">
                        {{form.email.label}}
                        {{form.email}}
                        {% if form.errors.email %}
                            <label for="" class="error">{{form.errors.email|striptags}}</label>
                        {% endif %}
                    </div>
    
                    <div class="col-md-3">
                        {{form.date_of_birth.label}}
                        {{form.date_of_birth}}
                        {% if form.errors.date_of_birth %}
                            <label for="" class="error">{{form.errors.date_of_birth|striptags}}</label>
                        {% endif %}
                    </div>
                </div>
    
                <div class="row" style="margin-top: 25px;">
                    <div class="col-md-3">
                        {{form.password.label}}
                        {{form.password}}
                        {% if form.errors.password %}
                            <label for="" class="error">{{form.errors.password|striptags}}</label>
                        {% endif %}
                    </div>
                </div>
    
                <div class="row" style="margin-top: 25px;">
    
                    <div class="col-md-3">
                        {{form.confirm_password.label}}
                        {{form.confirm_password}}
                        {% if form.errors.confirm_password %}
                        <label for="" class="error">{{form.errors.confirm_password|striptags}}</label>
                        {% endif %}
                    </div>
    
                    <div class="col-md-12" style="margin-top: 25px;">
                        <input type="submit" class="btn btn-sm btn-primary" value="submit">
                    </div>
                </div>
            </form>
        </div>
    </body>                
</html>

This is how our form will look when we go to route user/profile/create.

User Profile Form

  • The message displays success message once messages.add_message(request, messages.SUCCESS, ".....") is called it is just like the flash message.
  • The form.errors is called on validation has failed.
  • The form.non_field_errors display errors on top of form this errors are not associated to a particular field.
  • The form.errors. displays the error of the particular field.

This is how errors are displayed in the form.

User Profile Form Displaying Validation Errors

Saving Form

In urls.py file add routes to save the form.

urlpatterns = [
    path('user/profile/save', views.user_profile_create, name='user-profile-save'),
]

In views.py file add function user_profile_save() to save form data.

def user_profile_save(request):

    form = UserForm(request.POST)

    if form.is_valid():

        query = {
            "first_name" : form.cleaned_data.get('first_name'),
            "last_name" : form.cleaned_data.get('last_name'),
            "username" : form.cleaned_data.get('username'),
            "password" : make_password(form.cleaned_data.get('password')),
            "email" : form.cleaned_data.get('email'),
            "is_superuser" : 0,
            "is_staff" : 1,
            "is_active" : 1,
        }

        user = User.objects.create(**query)
        
        query={
            "user_id" : user.id,
            "dob" : form.cleaned_data.get('dob'),
        }
        
        AuthUserProfile.objects.create(**query)
        
        messages.add_message(request, messages.SUCCESS, "User Profile created successfully.")
        
        return HttpResponseRedirect(reverse('forms:user-profile-create'))
    
    template="forms/user_profile_create_form.html"
    
    return render(request,template,{"form":form})

The request.POST is passed to UserForm(request.POST) this binds the submitted data to Form Class.
The form.is_valid() returns a Boolean value if True then the form is clean and if False then there may be validation error.
To view validation errors after .is_valid() method we can print form.errors to view validation errors.

Calling form.cleaned_data.get('') gives use of the sanitized value to that field. Inside .is_valid() we have called model methods to save form data.

Showing success message on successfully validating form and saving its contents into the database

Form Validation User-Defined functions

To defined a custom validation function in Form Class name function with prefix clean followed by underscore and field name which must be validated.

Example

def clean_first_name(self):
    pass #this validates field first_name

def clean_username(self):
    pass #this validates field username

If the value of the field is not as expected that you can raise validation error or add error by mentioning field name self.add_error('field_name', "Error Message").
If you want to raise non-field error than set the first argument of add_error() method None followed by the message you want to be displayed.

self.add_error(None, msg) #this creates a non-field error

Note

For More information on Django, Forms visit the official website.

Conclusion

We have come to the end of our post on Django Form Validation.
If you have any doubts or suggestions please mention in the comments section and we’ll reach you soon and we would also love to hear requests and your recommendations for new tutorials/posts.

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