1. Scope v.s. Class method 2. How do we usually fix N+1 query 3. How to fix N+1 query when more scoping - preloding scope Reference article: https://www.justinweiss.com/articles/how-to-preload-rails-scopes/ https://www.justinweiss.com/articles/should-you-use-scopes-or-class-methods/

1. HOW TO FIX N+1 QUERY
WITH PRELOADING SCOPE
Reference articles:
Justin Weiss, How to Preload Rails Scopes and Why use scopes when we already have class methods?
Yiming Tsai @ Backer-Founder

2. SCOPE V.S. CLASS METHOD
class Reward
scope :updated_since, -> (time) { where(“reward.updated_at > ?”, time) }
#scope :updated_since, -> (time) { where(updated_at: (time..Time.now)) }
end
class self.updated_since(time)
if time.present?
where(“reward.updated_at > ?”, time)
else
all
end
end
Scope
Class
Method
Usage Reward.updated_since(1.day.ago)

3. Class
Method
Simple definition & Handle conditions for you
Complicated logic
SCOPE V.S. CLASS METHOD
Scope

4. HOW WE USUALLY FIX N+1 QUERY
Project.limit(5).map do |project|
project.rewards.length
end
class Project
has_many :rewards
end
class Reward
belongs_to :project
end
Project.includes(:rewards).limit(5).map do |project|
project.rewards.length
end
Model
N+1 query
Solution

5. WITH SCOPE..
Project.limit(5).map do |project|
project.rewards.publish.length
end
class Project
has_many :rewards
end
class Reward
belongs_to :project
enum [:draft, :publish]
end
Project.includes(:rewards).limit(5).map do |project|
project.rewards.publish.length
end
Model
N+1 query
Solution

6. SOLUTION
class Project
has_many :rewards
has_many :publish_rewards, -> { publish }, class_name: “Reward”
end
Project.includes(:publish_review).limit(5).map do |project|
project.publish_review.length
end
Model
Code