Format validation in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is format validation in Rails?

Format validation checks if a model attribute matches a specific pattern, usually using regular expressions, to ensure data is in the correct form.

beginner

How do you add a format validation to a Rails model attribute?

Use validates :attribute, format: { with: /regex/, message: 'error message' } inside the model to enforce a pattern.

beginner

Why use format validation instead of just presence validation?

Presence validation only checks if a value exists, but format validation ensures the value follows a specific pattern, like an email or phone number format.

intermediate

Example: Validate an email format in a Rails model.

Use validates :email, format: { with: URI::MailTo::EMAIL_REGEXP, message: 'must be a valid email' } to check email format.

beginner

What happens if a format validation fails when saving a Rails model?

The model will not save, and the error message defined in the validation will be added to the model's errors, which can be shown to the user.

Which method is used to add format validation in a Rails model?

A validate_format_of :attribute

B check_format :attribute, regex

C validates :attribute, format: { with: /regex/ }

D format_validation :attribute

The correct syntax is validates :attribute, format: { with: /regex/ }.

What does the with option specify in format validation?

A The error message to show

B The regular expression pattern to match

C The attribute name

D The validation context

The with option defines the regex pattern the attribute must match.

If a format validation fails, what happens when you try to save the model?

A The model does not save and adds errors

B The model saves without validation

C The model saves but logs a warning

D The model saves and ignores the format

The model will not save and will add error messages for the failed validations.

Which built-in regex can you use to validate emails in Rails?

A /\A[^@]+@[^@]+\z/

B EMAIL_VALIDATOR

C /email_regex/

D URI::MailTo::EMAIL_REGEXP

Rails provides URI::MailTo::EMAIL_REGEXP as a standard email regex.

Can format validation be used to check phone number patterns?

A Yes, by providing a suitable regex

B No, only emails are supported

C Only numeric validations are allowed

D Format validation is not for phone numbers

Format validation works with any regex pattern, including phone numbers.

Explain how to add a format validation to a Rails model attribute and why it is useful.

Think about how you tell Rails to check a pattern for an attribute.

Describe what happens when a format validation fails during model saving in Rails.

Consider the flow of validation and saving.