Arel::SelectManager 如何访问包括投影在内的结果

Question

我正在尝试访问连接的结果，其中两个表的列都被指定为投影的一部分。

我有 2 个模型（Rails 4.2.11；Arel 6.0.4；Ruby 2.5.3）

# Table name: users
#
#  id         :integer          not null, primary key
#  name       :string(255)
#  email      :string(255)
#  created_at :datetime         not null
#  updated_at :datetime         not null

class User < ActiveRecord::Base
  has_many :photos
end

# Table name: photos
#
#  id            :integer          not null, primary key
#  name          :string(255)
#  created_by_id :integer
#  assigned_id   :integer
#  created_at    :datetime         not null
#  updated_at    :datetime         not null
#  user_id       :integer

class Photo < ActiveRecord::Base
  belongs_to :user
end

creators = User.arel_table.alias('creators')
updaters = User.arel_table.alias('updaters')
photos = Photo.arel_table

photos_with_credits = photos.
join(photos.join(creators, Arel::Nodes::OuterJoin).on(photos[:created_by_id].eq(creators[:id]))).
join(photos.join(updaters, Arel::Nodes::OuterJoin).on(photos[:assigned_id].eq(updaters[:id]))).
project(photos[:name], photos[:created_at], creators[:name].as('creator'), updaters[:name].as('editor'))

# generated SQL
SELECT photos.name, photos.created_at, creators.name AS creator, updaters.name AS editor 
FROM photos 
INNER JOIN (SELECT FROM photos LEFT OUTER JOIN users creators ON photos.created_by_id = creators.id) 
INNER JOIN (SELECT FROM photos LEFT OUTER JOIN users updaters ON photos.updated_by_id = updaters.id)

我想如何处理结果

photos_with_credits.map{|x| "#{photo.name} - copyright #{photo.created_at.year} #{photo.creator}, edited by #{photo.editor}"}.join('; ')

这可能是一个非常愚蠢的问题，但是...... 由于 map 已从 SelectManager 类中弃用（并删除），因此我无法找到一种方法来使用 SelectManager 结果来产生有意义的输出。

感谢您的帮助。

Answer 1

简化了 activerecord / arel 查询生成器

修改代码

photos_with_credits = Photo.select([photos[:name], photos[:created_at], creators[:name].as('creator'), updaters[:name].as('editor')]).
joins(photos.outer_join(creators).on(photos[:created_by_id].eq(creators[:id])).join_sources).
joins(photos.outer_join(updaters).on(photos[:assigned_id].eq(updaters[:id])).join_sources)

photos_with_credits.map do |photo|
  puts "#{photo.name} - copyright #{photo.created_at.year} #{photo.creator}, edited by #{photo.editor}".light_blue
end

修正 SQL（更简单）

SELECT photos.name, photos.created_at, creators.name AS creator, updaters.name AS editor 
FROM photos 
    LEFT OUTER JOIN users creators ON photos.created_by_id = creators.id 
    LEFT OUTER JOIN users updaters ON photos.assigned_id = updaters.id

Answer 2

我们应该想办法触发SelectManage并得到ActiveRelation结果，然后我们可以通过使用map等来迭代它。

所以我想建议：

Photo.join(photos_with_credits.join_sources).map do |photo|
  "#{photo.name} - copyright #{photo.created_at.year} #{photo.creator}, edited by #{photo.editor}"}.join('; ')
end