ActiveRelation需要嵌套的联接使用范围 [英] ActiveRelation that requires nested joins using scopes

问题描述

我是新来的轨道。有一个爆炸。查询API，虽然是给我 有些麻烦。我一直在放大，做了很多的东西非常快， 但是这是第一次我花了几个小时试图弄明白。 它不喜欢什么，我以前用过的 - 常规的SQL，或休眠状态， 或什么的。

I am new to rails. Having a blast. The query API though is giving me some trouble. I've been zooming and doing a lot of stuff very quickly, but this is the first time I have spent hours trying to figure it out. It's not like anything I've used before - regular SQL, or Hibernate, or whatever.

该模型我已经是pretty的简单。

The model I have is pretty simple.

• 系统PrivateMessage有许多收件人
• 在收件人有一个接收器（哪一类用户的）
  • 在接收方也有场is_read'和'IS_DELETED
  • A PrivateMessage has many Recipients
  • A Recipient has a Receiver (which of class User)
    • recipient also has fields for 'is_read' and 'is_deleted'

    我的目标是建立一个查找所有未读，不会被删除查询 私人讯息​​给定用户。要做到这一点，我们需要加入 private_messages到收件人......然后'收件人'到 用户。

    My goal is to build a query that finds all the unread and not deleted private messages for a given user. To accomplish this, we need to join 'private_messages' to 'recipients'... and then 'recipients' to 'users'.

    下面是有关用户模型code：

    Here's the relevant User model code:

    has_many :sent_messages, :class_name => 'PrivateMessage', :foreign_key => 'sender_id'
    has_many :recipient_of_messages, :class_name => 'Recipient', :foreign_key => 'receiver_id'
    
    scope :by_id, lambda { |id| where(:id => id) } 
    

    我的收件人模式具有以下相关code：

    My Recipient model has the following relevant code:

    belongs_to :receiver, :class_name => 'User', :foreign_key => "receiver_id"
    belongs_to :private_message
    
    scope :unread, where(:is_read => false).where(:is_deleted => false)
    scope :by_receiver_id, lambda { |id| Recipient.joins(:receiver).merge(User.by_id(id)) }
    scope :unread_by_receiver_id, lambda { |id| unread.by_receiver_id(id) }
    

    当单独测试，该工程100％。

    When tested in isolation, this works 100%.

    然而，当我code中的私人信息查询，我遇到的问题。

    However, when I code the private message queries, I run into problems.

    belongs_to :sender, :class_name => 'User'
    has_many :recipients, :class_name => 'Recipient'
    
    scope :sorted, order("private_messages.created_at desc")
    scope :non_deleted, where(:is_deleted_by_sender => false)
    scope :non_deleted_by_sender_id, lambda { |id| sorted.non_deleted.joins(:sender).merge(User.by_id(id)) }
    
    # this scope does not work
    scope :non_deleted_by_receiver_id, lambda { |id| sorted.joins(:recipients).merge(Recipient.by_receiver_id(id)) }
    scope :newest, sorted.limit(3)
    
    # this scope does not work either
    scope :newest_unread_by_receiver_id, lambda { |id| newest.joins(:recipients).merge(Recipient.unread_by_receiver_id(id)) }
    

    当我尝试使用newest_unread_by_receiver_id'或'non_deleted_by_receiver_id'，我得到了以下异常：

    When I try and use 'newest_unread_by_receiver_id' or 'non_deleted_by_receiver_id', I get the following exception:

    ActiveRecord::ConfigurationError: Association named 'receiver' was not found; perhaps you misspelled it?
    

    这没有多大意义的，我......因为如果名字被拼写 错了，为什么没有当我测试它隔离失败？

    This doesn't make much sense to me... because if the name was spelled wrong, why doesn't it fail when I test it isolation?

    有人能帮助我吗？这一个是我发疯。有时 就是这样，我只是想在完整SQL编程或休眠QL所以我只能用它做：（

    Can someone help me out please? This one is driving me nuts. At times like this, I just want to program in full sql or Hibernate QL so I could just be done with it :(

    如果我只是接近问题完全错误的，那么我会AP preciate它，如果你只是让我知道这一点。我在使用作用域和ActiveRelation是一路前进中的Rails 3.1的IM pression。

    If I'm just approaching the problem totally wrong, then I'd appreciate it if you just let me know that too. I am under the impression that using scopes and ActiveRelation was the way moving forward in Rails 3.1.

    感谢

    推荐答案

    我可能会用这样的事情。我不停的范围分隔清晰。

    I would probably use something like this. I kept scopes separate for clarity.

    模型（改名PrivateMessage - >和收件人 - > MessageCopy）：

    Models (renamed PrivateMessage -> Message and Recipient -> MessageCopy):

    class User < ActiveRecord::Base
      has_many :sent_messages, :class_name => "Message", :foreign_key => :sender_id
      has_many :sent_message_copies, :through => :sent_messages, :source => :message_copies
      has_many :received_messages, :through => :received_message_copies, :source => :message
      has_many :received_message_copies, :class_name => "MessageCopy", :foreign_key => :recipient_id
    end
    
    class Message < ActiveRecord::Base
      belongs_to :sender, :class_name => "User"
      has_many :message_copies
      has_many :recipients, :through => :message_copies
    end
    
    class MessageCopy < ActiveRecord::Base
      belongs_to :message
      belongs_to :recipient, :class_name => "User"
      scope :unread, where(:read => false)
      scope :undeleted, where(:deleted => false)
      scope :sent_to, lambda { |recipient| where(:recipient_id => recipient.id) }
    end
    

    模式（迁移将采取太多的空间，在这里）：

    Schema (migrations would have taken too much space here):

    ActiveRecord::Schema.define(:version => 20110503061008) do
      create_table "message_copies", :force => true do |t|
        t.boolean  "read",         :default => false
        t.boolean  "deleted",      :default => false
        t.integer  "message_id"
        t.integer  "recipient_id"
      end
      create_table "messages", :force => true do |t|
        t.string   "title"
        t.integer  "sender_id"
      end
      create_table "users", :force => true do |t|
        t.string   "name"
      end
    end
    

    - 修改

    --edit

    示例查询中使用联接返回的消息

    Message.joins(:message_copies).where(:message_copies => {:read => false, :deleted => false, :recipient_id => 3})
    

    信息范围重复使用于其他型号范围

    scope :non_deleted_by_recipient, lambda { |recipient|
      joins(:message_copies).merge(MessageCopy.unread.undeleted.sent_to(recipient))
    }
    

    - EDIT2

    --edit2

    这Railscast具有很好的例子的两个连接和范围：

    This Railscast has nice examples of both joins and scopes:

    • http://railscasts.com/episodes/215-advanced-查询功能于轨道-3

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