ActiveRecord Features

Question 1

How to add a scope?

Answer 1

scope :scope_sample, -> { where(name: ‘d’) }

Question 2

How to add a scope inside another scope?

Answer 2

scope :scope_sample, -> { where(name: ‘d’) }

scope :another_scope, -> { scope_sample.where(email: ‘a’) }

Question 3

How to add a scope with params?

Answer 3

scope :scope_sample, ->(name) { where(name: name) }

User.scope_sample(‘a’)

Question 4

How to add a default scope?

Answer 4

default_scope { where(name: ‘d’) }

Question 5

How to remove default scope?

Answer 5

User.unscoped

Question 6

What the main callback do you know? ( 4 )

Answer 6

before_destroy :sample
  before_create :sample
  after_create :sample
  before_save :sample
  after_save :sample
  before_validation :sample
  after_validation :sample

def sample
p “Hello”
end

Question 7

How to add attribute options and convert types on a model level?

Answer 7

attribute :name, :integer, default: 10

Question 8

Why do we need serialize in a model?

Answer 8

It allows us to store value in text format in the database and then to transform to whatever you need. ( To hash for example )

Question 9

How to use serialization?

Answer 9

serialize :description, Hash

# User.create(description: {a: 1 })
# creates "description", "---\n:a: 1\n"
# User.last.description
# => {:a=>1}

Question 10

What is active_record store?

Answer 10

It’s the same as serialization

serialize :description, Hash
# or
store :description

Question 11

What is enum?

Answer 11

Allows you to set a restriction for field values ( from speciific array)

Question 12

How to add enum?

Answer 12

enum status: [:my_invalid, :my_valid]

add integer field to the db ( because it’s store only index)

Question 13

How to set index explicitly to enum field?

Answer 13

enum status: { my_invalid: 0, my_valid: 1 }

Question 14

How to use enum helpers? ( 3 ways )

Answer 14

class User < ApplicationRecord
  enum status: [:my_invalid, :my_valid]
end

1. check current status

# user.my_invalid? 
# user.my_valid?

2. update status

# user.my_invalid! 
# user.my_valid!

3. return scope

# User.my_invalid 
# returns all record with this status