Rails 4 急切加载多个表答案

【问题标题】：Rails 4 eager loading with multiple tablesRails 4 急切加载多个表
【发布时间】：2014-05-09 01:38:00
【问题描述】：

我正在尝试使用 5 个表加载结果：

class Meeting < ActiveRecord::Base
  has_many :bookings
end

class Booking < ActiveRecord::Base
  belongs_to :user
  belongs_to :meeting
  belongs_to :role
  belongs_to :group
end

class Group < ActiveRecord::Base
  has_many :group_memberships
  has_many :users, through: :group_memberships
end

class GroupMembership < ActiveRecord::Base
  belongs_to :group
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :group_memberships
  has_many :groups, through: :group_memberships
end

在 MeetingController.rb 中：

def index
    @meetings = Meeting.where(year: @year)
end

我正在尝试使用 includes(:bookings) 但根据bullet-gem 急加载不起作用。在我看来，我称之为这条线：

@meetings.each do |meeting|
  meeting.bookings.find_by(group: @group, role: @role)
end

我收到了多段 52 行代码，这显然意味着我并不急于加载任何数据：

Booking Load (0.1ms)  SELECT "bookings".* FROM "bookings" WHERE "bookings"."meeting_id" = ? AND "bookings"."user_id" = 8 AND "bookings"."group_id" = 2 LIMIT 1  [["meeting_id", 207]]
  Rendered shared/_book.html.haml (1.0ms)
  Booking Load (0.1ms)  SELECT "bookings".* FROM "bookings" WHERE "bookings"."meeting_id" = ? AND "bookings"."group_id" = 2 AND "bookings"."role_id" = 4 LIMIT 1  [["meeting_id", 208]]
  Booking Load (0.0ms)  SELECT "bookings".* FROM "bookings" WHERE "bookings"."meeting_id" = ? AND "bookings"."user_id" = 8 AND "bookings"."group_id" = 2 LIMIT 1  [["meeting_id", 208]]
  Rendered shared/_book.html.haml (1.0ms)
  Booking Load (0.1ms)  SELECT "bookings".* FROM "bookings" WHERE "bookings"."meeting_id" = ? AND "bookings"."group_id" = 2 AND "bookings"."role_id" = 4 LIMIT 1  [["meeting_id", 209]]

bullet.log：

2014-03-29 15:30:48[WARN] user: karlingen
localhost:3000http://localhost:3000/meetings/host
Unused Eager Loading detected
  Meeting => [:bookings]
  Remove from your finder: :include => [:bookings]

任何想法我应该做什么？

【问题讨论】：

你能把子弹的日志也包括进去吗？
@vee 我已经添加了。
我猜你不能在集合上使用 find_by 并期望它不会发出 SQL 查询。你需要使用某种红宝石的select。
karlingen，试试这个 -> Meeting.includes(:bookings).where(year: @year).references(:bookings)

标签： ruby-on-rails ruby ruby-on-rails-4 associations eager

【解决方案1】：

尝试以下方法：

@meetings = Meeting.includes(:bookings).where(year: @year)

另外，你在@year 中过得怎么样？

【讨论】：

【解决方案2】：

Meeting.includes(:bookings).where(year: @year).references(:bookings)

如果您使用的是 rails 4，则可以使用。

【讨论】：