rails 4有很多通过关联查询

Question

我有这些模型，但是当我执行 Message.last.people 或 Message.last.recipient_lists 时出现错误。我如何引用收件人列表或附加到具有活动记录的邮件的人员？我需要做一个 RecipientList.where(:message => Message.last) 吗？似乎应该有更好的方法通过 .message 来做到这一点？

class Message < ActiveRecord::Base
    has_many   :people, through: :recipient_list
end

class Person < ActiveRecord::Base
  has_many :messages, through: :recipient_list
end

class RecipientList < ActiveRecord::Base
    belongs_to :person
    belongs_to :message
end

我收到这个错误

Message.last.recipient_lists
Message Load (0.7ms) SELECT "messages".* FROM "messages" ORDER BY "messages"."id" DESC LIMIT 1 NoMethodError: undefined method `recipient_lists' for

from /home/nick/.rvm/gems/ruby-2.0.0-p598/gems/activemodel-4.0.9/lib/active_model/attribute_methods.rb:439:in

method_missing' from /home/nick/.rvm/gems/ruby-2.0.0-p598/gems/activerecord-4.0.9/lib/active_record/attribute_methods.rb:168:in method_missing' from (irb):1 from /home/nick/.rvm/gems/ruby-2.0.0-p598/gems/railties-4.0.9/lib/rails/commands/console.rb:90:in start' from /home/nick/.rvm/gems/ruby-2.0.0-p598/gems/railties-4.0.9/lib/rails/commands/console.rb:9:in start' from /home/nick/.rvm/gems/ruby-2.0.0-p598/gems/railties-4.0.9/lib/rails/commands.rb:62:in <top (required)>' from bin/rails:4:inrequire' from bin/rails:4:in `'

Message.last.people Message Load (1.0ms) SELECT "messages".* FROM "messages" ORDER BY "messages"."id" DESC LIMIT 1 ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :recipient_list in model Message

Answer 1

您需要在 Message 和 Person 中明确包含 has_many :recipient_lists，并在 through: 选项中正确复数 :recipient_lists，如下所示：

class Message < ActiveRecord::Base
  has_many :recipient_lists
  has_many :people, through: :recipient_lists
end

class Person < ActiveRecord::Base
  has_many :recipient_lists
  has_many :messages, through: :recipient_lists
end

class RecipientList < ActiveRecord::Base
  belongs_to :person
  belongs_to :message
end