转换选择和收集方法为连接 [英] convert select and collect methods into joins

问题描述

我学习联接我有三个型号

I am learning joins I have three models

class Booking < ActiveRecord::Base
  has_and_belongs_to_many :groups
  has_and_belongs_to_many :users
end

class User < ActiveRecord::Base
  belongs_to :group
  has_and_belongs_to_many :bookings
end

class Group < ActiveRecord::Base
  has_many :users
  has_and_belongs_to_many :bookings
end

booking = Booking.first
booking.groups.collect{|g| g.users.select{|u| !self.users.include? u}}.flatten

我想这是不是在预订团体预订的所有用户提供一些这样的事

I want to get all users which are not booked in booking groups some thing like this

booking=Booking.first
booking.groups.collect{|g| g.users.select{|u| !self.users.include? u}}.flatten

我

如何才能做到这一点的联接，而不是收集和选择？

How can I do it with joins instead collect and select?

推荐答案

这应该是这样的（使用的 AREL 宝石）：

It should be something like (using arel gem):

class User < ActiveRecord::Base
   scope :non_booked_for, ->(booking_id) {
      users = User.arel_table
      bookings = Booking.arel_table
      groups = Group.arel_table
      where(groups_bookings[:booking_id].eq(booking_id)
       .and(groups_bookings[:group_id].eq(users[:group_id])))
       .not.where(user_bookings[:user_id].eq(users[:id])
             .and(user_bookings[:booking_id].eq(booking_id)))
   end
end

用法：

users = User.non_booked_for Booking.first.id

它只是使用否定所有的用户，这属于组和预订，其组所属的预订了。但我不肯定的否定将正常工作在这里，所以应该进行调试。并请在这两个表名称： users_bookings 或 bookings_users 的关联，因此，例如，模型会导致：

It just uses negation to all users, which belong to group and bookings, and its group belongs to that booking too. But I'm not sure that the negation will work properly here, so it should be debugged. And please select on of the two table names: users_bookings, or bookings_users for the associations, so, for example, in models it will lead to:

has_and_belongs_to_many :users

has_and_belongs_to_many :bookings, table_name: :users_bookings

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