ruby-on-rails - Rails Associations Riddle : User, 讲师、学生和事件

Question

我用谷歌搜索、阅读了文档并观看了 railscast，但我无法理解这一点。请帮忙。我在 Ubuntu 13.04 上运行最新的稳定版 Rails 和 Ruby 1.9.3。

我有一个User 模型和一个Event 模型。现在，两者之间存在 has_and_belongs_to_many 关系。

然而，在现实生活中，User 与 Event 相关，作为 Lecturer 或 Student .User 可以同时是 Student 和 Lecturer，但不能用于同一事件。Lecturer 或 Student 还不是我应用程序中的模型，我不确定它们是否应该是单独的模型。我需要帮助来实现这个逻辑。

我想要实现的是这样的:

Event.first.lecturers # 应该返回作为此特定事件的讲师的用户。

Event.first.students # 应返回此特定事件的学生用户

User.first.events :as => :student # 应该返回特定用户的事件用户是学生

User.first.events :as => :lecturer # 应该为特定用户返回事件用户是讲师

我在想也许 has_many :through 关联可能有效，但我很困惑。任何和所有指导表示赞赏。

问候，

纳迪姆

Answer 1

您可以创建两个连接表 events_students 和 events_lecturers 并像这样设置模型

class Event < ActiveRecord::Base
  has_and_belongs_to_many :students, :class_name => 'User', :join_table => :events_students, :association_foreign_key => :user_id
  has_and_belongs_to_many :lecturers, :class_name => 'User', :join_table => :events_lecturers, :association_foreign_key => :user_id
end

class User < ActiveRecord::Base
  has_and_belongs_to_many :student_events, :class_name => 'Event', :join_table => :events_students, :association_foreign_key => :event_id
  has_and_belongs_to_many :lecturer_events, :class_name => 'Event', :join_table => :events_lecturers, :association_foreign_key => :event_id
end

然后访问它:

Event.first.students
Event.first.teachers
User.first.student_events
User.first.lecturer_events

更新。

另一种解决方案是使用 has_many :through

class User < ActiveRecord::Base 
  has_many :event_assignments
  has_many :student_events, :through => :event_assignments, :source => :event, :conditions => {'event_assignments.type' => 'EventAssignment::Student'}
  has_many :lecturer_events, :through => :event_assignments, :source => :event, :conditions => {'event_assignments.type' => 'EventAssignment::Lecturer'}
end

class Event < ActiveRecord::Base 
  has_many :event_assignments
  has_many :students, :through => :event_assignments, :source => :user, :conditions => {'event_assignments.type' => 'EventAssignment::Student'}
  has_many :lecturers, :through => :event_assignments, :source => :user, :conditions => {'event_assignments.type' => 'EventAssignment::Lecturer'}
end

class EventAssignment < ActiveRecord::Base 
  belongs_to :user
  belongs_to :event
end

class EventAssignment::Student < EventAssignment
end

class EventAssignment::Lecturer < EventAssignment
end

我将 STI 用于 EventAssignment 模型，因为如果您对不同类型的分配有不同的逻辑，它会很有用。但是如果不需要它，只需在连接模型中使用另一个列名而不是 type 来标识关系类型:

class User < ActiveRecord::Base 
  has_many :event_assignments
  has_many :student_events, :through => :event_assignments, :source => :event, :conditions => {'event_assignments.kind' => 'student'}
  has_many :lecturer_events, :through => :event_assignments, :source => :event, :conditions => {'event_assignments.kind' => 'lecturer'}
end

class Event < ActiveRecord::Base 
  has_many :event_assignments
  has_many :students, :through => :event_assignments, :source => :user, :conditions => {'event_assignments.kind' => 'student'}
  has_many :lecturers, :through => :event_assignments, :source => :user, :conditions => {'event_assignments.kind' => 'lecturer'}
end

class EventAssignment < ActiveRecord::Base 
  belongs_to :user
  belongs_to :event
end