Custom form validation methods in Django - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of custom form validation methods in Django?

Custom form validation methods let you check user input beyond basic rules. They help ensure data is correct and meaningful before saving or processing.

beginner

How do you name a method to validate a specific field in a Django form?

Name the method clean_fieldname, replacing fieldname with your form field's name. Django calls it automatically to validate that field.

beginner

What should a clean_fieldname method return in Django?

It should return the cleaned (validated and possibly modified) value for that field. If invalid, it should raise ValidationError.

intermediate

What is the difference between clean_fieldname and clean() methods in Django forms?

clean_fieldname validates one field at a time. clean() validates the whole form and can check multiple fields together.

beginner

How do you raise a validation error inside a custom validation method?

Use <code>from django.core.exceptions import ValidationError</code> and then raise <code>ValidationError('Your error message')</code> when validation fails.

Which method name will Django call automatically to validate a form field named 'email'?

A clean_email

B validate_email

C check_email

D cleanField_email

Django calls methods named clean_ automatically for field validation.

What should a custom field validation method return if the input is valid?

A Nothing

B The cleaned value

C Raise ValidationError

D The original form instance

The method must return the cleaned (possibly modified) value for the field.

Where do you put validation logic that depends on multiple fields in a Django form?

A In the model's save method

B In clean_fieldname methods

C In the form's __init__ method

D In the clean() method

The clean() method validates the whole form and can access multiple fields.

What happens if you raise ValidationError inside a custom validation method?

A The form is invalid and shows the error message

B The form saves anyway

C The server crashes

D The error is ignored

Raising ValidationError stops form validation and shows the error to the user.

Which import is needed to raise a ValidationError in Django forms?

A import ValidationError from django

B from django.forms import ValidationError

C from django.core.exceptions import ValidationError

D from django.validation import ValidationError

ValidationError is imported from django.core.exceptions.

Explain how to create a custom validation method for a single field in a Django form.

Think about method naming and what it returns or raises.

Describe when and why you would use the clean() method in a Django form.

Consider validation that depends on more than one field.