Custom form validation methods in Django - Mini Project: Build & Apply

Custom form validation methods

📖 Scenario: You are building a simple Django web app where users submit their profile information through a form. You want to make sure the data they enter is valid before saving it.

🎯 Goal: Create a Django form with custom validation methods to check user input for specific rules.

📋 What You'll Learn

Create a Django form class called UserProfileForm with fields username and age.

Add a custom validation method to check that username is at least 5 characters long.

Add a custom validation method to check that age is at least 18.

Raise appropriate validation errors if the rules are not met.

💡 Why This Matters

🌍 Real World

Custom form validation is essential in web apps to ensure users enter correct and safe data before saving it to the database.

💼 Career

Understanding how to write custom validation methods in Django forms is a key skill for backend web developers working with user input and data integrity.

1

Create the initial form class with fields

Create a Django form class called UserProfileForm that inherits from forms.Form. Add two fields: username as a forms.CharField and age as a forms.IntegerField.

Django

from django import forms

# Your code here

Need a hint?

Use class UserProfileForm(forms.Form): to start the form class. Add fields as class variables.

2

Add a custom validation method for username length

Inside the UserProfileForm class, add a method called clean_username that checks if the username is at least 5 characters long. If it is shorter, raise forms.ValidationError with the message 'Username must be at least 5 characters long.'. Return the cleaned username if valid.

Django

from django import forms

class UserProfileForm(forms.Form):
    username = forms.CharField()
    age = forms.IntegerField()

    # Your code here

Need a hint?

Define clean_username(self) method. Use self.cleaned_data['username'] to get the value.

3

Add a custom validation method for minimum age

Inside the UserProfileForm class, add a method called clean_age that checks if the age is at least 18. If it is less, raise forms.ValidationError with the message 'You must be at least 18 years old.'. Return the cleaned age if valid.

Django

from django import forms

class UserProfileForm(forms.Form):
    username = forms.CharField()
    age = forms.IntegerField()

    def clean_username(self):
        username = self.cleaned_data['username']
        if len(username) < 5:
            raise forms.ValidationError('Username must be at least 5 characters long.')
        return username

    # Your code here

Need a hint?

Define clean_age(self) method. Use self.cleaned_data['age'] to get the value.

4

Complete the form with all validations

Ensure the UserProfileForm class includes both clean_username and clean_age methods with the validations as described. The form should be ready to use in a Django view for validation.

Django

from django import forms

class UserProfileForm(forms.Form):
    username = forms.CharField()
    age = forms.IntegerField()

    def clean_username(self):
        username = self.cleaned_data['username']
        if len(username) < 5:
            raise forms.ValidationError('Username must be at least 5 characters long.')
        return username

    def clean_age(self):
        age = self.cleaned_data['age']
        if age < 18:
            raise forms.ValidationError('You must be at least 18 years old.')
        return age

# Your code here

Need a hint?

Make sure both validation methods are present and correctly implemented.