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Scope in rails.

· 2 min read
Shekhar Patil
Shekhar Patil
Full stack developer.

Rails follow the DRY principle of software development and that is 'Don't Repeat Yourself'. Scopes is are great to keep our code DRY and well organized. It's just a set of pre-defined SQL queries that we can use to write complex queries.

Suppose we want to fetch users who have status active. So, we can simply write the following query


def index
  @active_users = User.where(status: "active")
end

But we may need to re-use this code multiple times in our project. So instead of writing the same code, again and again, we can define a scope for it.

class user < ActiveRecord::Base
  scope :active, -> { where(status: "active") }
end

Now, we can simply use an active scope to fetch all active users as following:

def index
  @active_users = User.active
end

1. Scope with parameter.​

we can give parameters to scope.

class Fruit < ActiveRecord::Base
  scope :color, -> (color_name){ where(color: color_name) }
end

now in our Fruit controller we can use

def Index
  @red_fruits = Fruit.color("red")
  @yellow_fruits = Fruit.color("yellow")
end

2. Scopes Are Chainable​

This is really interesting and it makes scope even more useful.

class User < ApplicationRecord
  scope :active, -> { where(status: "active") }
  scope :recent, -> { where('created_at < ?', 1.week.ago }
end

we can use it in the controller as following;

def index
  @users = User.active.recent
end

3. How exactly scope works in rails​

look at the active scope once again

class user < ActiveRecord::Base
  scope :active, -> { where(status: "active") }
end

we can achieve the same result using the following class method as given. Basically, instead of writing class method scope is syntactical sugar for writing queries.


def self.active
  User.where(status: "active")
end

I would love to hear some of the interesting topics related to rails which I can explore and write a blog about it on Twitter.

Cheers!