extract-query-objects.md

Extract Query Objects

http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models/

適合場景

如果有一些複雜的 scope 或者是 class method 放在 model 裡。可以試著搬出 ActiveRecord ，變成 Query Objects。

例如 AbandonedTrialQuery

class AbandonedTrialQuery
  def initialize(relation = Account.scoped)
    @relation = relation
  end

  def find_each(&block)
    @relation.
      where(plan: nil, invites_count: 0).
      find_each(&block)
  end
end

可以利用這樣的方式寄信

AbandonedTrialQuery.new.find_each do |account|
  account.send_offer_for_support
end

還可以這樣用

old_accounts = Account.where("created_at < ?", 1.month.ago)
old_abandoned_trials = AbandonedTrialQuery.new(old_accounts)

My Example

before

lib/tasks/drop_registrants_if_unpaid.rake

   registrants = Registrant.where(:paid_at => nil).where(["cancelled_at = ? ", nil ]).where("created_at <= ?", Time.now - 3.days)

    registrants.each do |registrant|
      registrant.cancelled_by_system_due_to_not_paid!
    end

after

app/models/need_cancelled_registrant.rb

class NeedCancelledRegistrant
  def initialize(relation = Registrant.scoped)
    @relation = relation
  end

  def find_each(&block)
    @relation.
      not_paid.not_cancelled.register_days_ago(3).
      find_each(&block)
  end
end

lib/tasks/drop_registrants_if_unpaid.rake

NeedCancelledRegistrant.new.find_each do |r|
  r.cancelled_by_system_due_to_not_paid!
end