Patterns in Ruby: Service object

[joshmfrankel]

The Service Object Pattern

Description

• Change Something / Return Nothing
• Perform a single unit of business logic
• File name describes the side effect

When to use it

• You have a single contained unit of business logic
• You need to execute a series of steps
• You want to initiate a side-effect

When not to use it (Anti-patterns)

• You have made all objects into Services - Everything is a Service (spoiler: it isn't)
• You are mixing querying and command pattern
• You have service objects that are actually multiple service objects (God Objects)

Before

class UsersController < ApplicationController
  def create
    user = User.new(user_params)

    if user.save
      UserMailer.sign_up.deliver_later
      
      Subscription.create(status: "active", user:)
      Analytics::UserSignUpEvent.track(user)

      head 200
    else
      head 400
    end
  end
end

After

class CreateUserService < ApplictionService

  def initialize(user:)
    @user = user
  end

  def call
    User.transaction do
      user.save

      UserMailer.sign_up.deliver_later
      Subscription.create(status: "active", user:)
      Analytics::UserSignUpEvent.track(user)
    end
    
    true
  rescue SubscriptionError, UserError => e
    false
  end

  private

  attr_reader :user
end

class UsersController < ApplicationController
  def create
    user = User.new(user_params)
    service = CreateUserService.new(user:)

    if service.call
      head 200
    else
      head 400
    end
  end
end

Future

Result returning

class CreateUserService < ApplictionService

  def initialize(user:)
    @user = user
  end

  def call
    User.transaction do
      user.save

      UserMailer.sign_up.deliver_later
      Subscription.create(status: "active", user:)
      Analytics::UserSignUpEvent.track(user)
    end
    
    Success.new(user, "User created")
  rescue SubscriptionError, UserError => exception
    Failure.new(exception)
  end

  private

  attr_reader :user
end

class UsersController < ApplicationController
  def create
    user = User.new(user_params)
    service = CreateUserService.new(user:)
    service.call

    if service.success?
      render json: { error: service.message }
    else
      render json: { error: service.exception }
    end
  end
end