[RUBY] Master the [Rails] scope!

Explanation of scope

Set scope in model and call it with a controller or the like.

-Example- Set scope in User model. Called by the users controller.

app/models/user.rb

class User < ApplicationRecord
  ...
    # scope :Name to call, -> {processing}

    #Get the deleted column is false
    scope :active, -> { where(deleted: false) }
    # created_Get at column in descending order
    scope :sorted, -> { order(created_at: :desc) }
    #A combination of active and sorted
    scope :recent, -> { active.sorted }
  ...
end

app/controllers/users_controller.rb

class UsersController < ApplicationController
  ...
  def index
  # @users =model.scope name

    @users = User.recent
  end
  ...
end

How to use lambda

lambda is an anonymous function. Furthermore, the identity of the anonymous function is a Ruby Proc object. Anonymous functions are, as they are, "unnamed functions". Something like the code below is called an anonymous function. (* Both codes are synonymous.)

nameless_func = lambda { |n| n**2 }
nameless_func.(5)
#=> 25

scope :nameless_func, -> { |n| n**2 }
nameless_func(5)
#=> 25

merit

--By defining the scope of the model, multiple queries can be combined into one method. --If you use scope rather than writing multiple queries in the controller, your code will be cleaner.