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

Recall & Review

beginner

What is the purpose of uniqueness validation in Rails?

Uniqueness validation ensures that a specific attribute value is unique in the database, preventing duplicate records for that attribute.

beginner

How do you add a uniqueness validation to a model attribute in Rails?

Use validates :attribute_name, uniqueness: true inside the model to enforce uniqueness on that attribute.

intermediate

Why should you add a unique index in the database when using uniqueness validation?

Because Rails validations run in application code and can miss race conditions, a unique database index ensures data integrity at the database level.

intermediate

What option do you use to make uniqueness validation case insensitive?

Use validates :attribute_name, uniqueness: { case_sensitive: false } to ignore case differences when checking uniqueness.

intermediate

How can you validate uniqueness scoped to another attribute in Rails?

Use validates :attribute_name, uniqueness: { scope: :other_attribute } to ensure uniqueness within the scope of another attribute.

Which Rails method adds uniqueness validation to a model attribute?

A validates :name, uniqueness: true

B validate_uniqueness_of :name

C unique :name

D validates_uniqueness :name

The correct syntax is validates :attribute, uniqueness: true.

Why is it important to add a unique index in the database when using uniqueness validation?

A To improve query speed

B To prevent race conditions causing duplicates

C To allow duplicate records

D To enable case insensitive checks

A unique index prevents duplicates even if two requests happen at the same time, which Rails validations alone cannot guarantee.

How do you make uniqueness validation ignore case differences?

A validates :attr, uniqueness: true, ignore_case: true

B validates :attr, case_insensitive: true

C validates :attr, uniqueness: { case_sensitive: false }

D validates :attr, uniqueness: false

Use case_sensitive: false option inside uniqueness validation to ignore case.

What does the scope option do in uniqueness validation?

A Makes validation faster

B Disables uniqueness validation

C Allows duplicates globally

D Limits uniqueness to a group of records sharing the same scope attribute

The scope option restricts uniqueness to records with the same value in the scoped attribute.

If you want to validate uniqueness of email ignoring case and scoped to account_id, which is correct?

A validates :email, uniqueness: { case_sensitive: false, scope: :account_id }

B validates :email, uniqueness: true, scope: :account_id

C validates :email, uniqueness: { scope: :account_id }

D validates :email, uniqueness: false

You combine case_sensitive: false and scope: :account_id inside uniqueness validation.

Explain how to enforce uniqueness validation on a Rails model attribute and why adding a unique database index is important.

Think about both application-level and database-level protections.

Describe how to make uniqueness validation case insensitive and scoped to another attribute in Rails.

Combine options inside the uniqueness hash.