需要使用范围进行嵌套连接的 ActiveRelation

我是 Rails 新手。玩得很开心。查询 API 给了我 有些麻烦。我一直在快速地缩放并做很多事情， 但这是我第一次花几个小时试图弄清楚。 它不像我以前使用过的任何东西——常规 SQL 或 Hibernate， 管他呢。

我的模型非常简单。

• 私人消息有多个收件人
• A Recipient has a Receiver (which of class User)
  • 收件人还有“is_read”和“is_deleted”字段

我的目标是建立一个查询来查找所有未读且未删除的内容 给定用户的私人消息。为了实现这一目标，我们需要加入 'private_messages' 到 'recipients'...然后 'recipients' 到 “用户”。

这是相关的用户模型代码：

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) } 

我的收件人模型具有以下相关代码：

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) }

单独测试时，此方法 100% 有效。

然而，当我编写私人消息查询代码时，我遇到了问题。

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”时，出现以下异常：

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

这对我来说没有多大意义......因为如果名字被拼写出来 错了，为什么我测试隔离时它没有失败？

有人可以帮我吗？这让我发疯。有时 像这样，我只想用完整的 sql 或 Hibernate QL 进行编程，这样我就可以完成它了:(

如果我完全错误地处理了这个问题，那么如果您也让我知道这一点，我将不胜感激。我的印象是，使用范围和 ActiveRelation 是 Rails 3.1 中前进的方向。

Thanks

我可能会使用这样的东西。为了清楚起见，我将范围分开。

Models（重命名为 PrivateMessage -> 消息和收件人 -> 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

Schema（迁移在这里会占用太多空间）：

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

--edit

使用连接返回消息的示例查询

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

消息范围在其他模型上重用范围

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

--edit2

这个 Railscast 有很好的连接和作用域示例：

• http://railscasts.com/episodes/215-advanced-queries-in-rails-3 http://railscasts.com/episodes/215-advanced-queries-in-rails-3