Conditional validations in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a conditional validation in Rails?

A conditional validation runs only when a specific condition is true. It helps check data only in certain cases, like validating a field only if another field has a certain value.

beginner

How do you use :if option in Rails validations?

You add :if with a method name, proc, or lambda that returns true or false. The validation runs only if it returns true.

beginner

Example: Validate presence of nickname only if user_type is 'guest'. How to write this?

Use validates :nickname, presence: true, if: -> { user_type == 'guest' }. This means nickname must be present only when user_type equals 'guest'.

intermediate

What is the difference between :if and :unless in Rails validations?

:if runs validation when condition is true. :unless runs validation when condition is false. They are opposites.

intermediate

Can you use multiple conditions in Rails validations? How?

Yes, you can combine :if and :unless or use methods that check multiple conditions. The validation runs only if all conditions are met.

Which option runs a validation only when a condition is true?

A :if

B :unless

C :only_if

D :when

The :if option runs the validation only if the given condition returns true.

What does this validation do? validates :email, presence: true, unless: :admin?

A Validates email presence only if user is not admin

B Validates email presence only if user is admin

C Always validates email presence

D Never validates email presence

The :unless option skips validation if the method admin? returns true, so it validates only if user is not admin.

How can you write a conditional validation using a method?

A validates :name, presence: true, if: method_name

B validates :name, presence: true, if: method_name()

C validates :name, presence: true, if: 'method_name'

D validates :name, presence: true, if: :method_name

You pass the method name as a symbol to :if, like if: :method_name, so Rails calls it to check the condition.

What type of object can you use with :if for conditional validation?

A Only symbols

B Symbols, procs, or lambdas

C Only strings

D Only booleans

:if accepts symbols (method names), procs, or lambdas that return true or false.

If you want a validation to run only when two conditions are true, what should you do?

A Use :if and :unless together

B Use two separate validations

C Combine conditions in one method or lambda for :if

D Use :only_if option

Combine the conditions inside one method or lambda and pass it to :if so validation runs only if all conditions are true.

Explain how to use conditional validations in Rails with examples.

Think about when you want validations to run only sometimes.

Describe the difference between :if and :unless in Rails validations and when to use each.

They are opposites controlling when validations run.