Scopes for reusable queries in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a scope in Rails?

A scope is a way to define reusable, named queries in a Rails model. It helps keep code clean by grouping common query logic.

beginner

How do you define a simple scope in a Rails model?

Use the scope method with a name and a lambda. Example: <br>scope :active, -> { where(active: true) }

beginner

Why use scopes instead of repeating query code?

Scopes make code easier to read, maintain, and reuse. They avoid repeating the same query logic in many places.

intermediate

Can scopes accept parameters? How?

Yes. You can pass parameters to scopes by using lambdas with arguments. Example: <br>scope :created_after, ->(date) { where('created_at > ?', date) }

intermediate

How do scopes chain together in Rails?

Scopes return ActiveRecord relations, so you can chain them like methods. Example: <br>User.active.created_after(Date.today) runs both queries together.

What does a Rails scope return?

A A SQL string

B An ActiveRecord relation

C A plain Ruby array

D A controller action

Scopes return ActiveRecord relations, allowing further chaining and lazy loading.

How do you define a scope named 'recent' that returns records created in the last 7 days?

A scope :recent, -> { where('created_at >= ?', 7.days.ago) }

B def recent; where('created_at >= ?', 7.days.ago); end

C scope recent = where('created_at >= ?', 7.days.ago)

D scope :recent { where('created_at >= ?', 7.days.ago) }

The correct syntax uses scope :name, -> { ... } with a lambda.

Which is a benefit of using scopes?

A They speed up the database

B They replace migrations

C They make queries reusable and readable

D They handle user authentication

Scopes help reuse query logic and improve code clarity.

Can you chain multiple scopes in Rails?

A Yes, scopes return relations that can be chained

B No, scopes must be called separately

C Only if they have no parameters

D Only inside controllers

Scopes return ActiveRecord relations, so chaining is supported.

How do you pass a parameter to a scope?

A Parameters are not supported in scopes

B Define a method instead of a scope

C Use a global variable inside the scope

D Use a lambda with an argument, e.g., <code>scope :by_status, ->(status) { where(status: status) }</code>

Scopes can accept parameters by defining lambdas with arguments.

Explain what a scope is in Rails and why it is useful.

Think about how you can avoid repeating the same query code.

Describe how to define a scope that accepts a parameter and how to use it.

Remember scopes are like methods that return queries.