Question

我用谷歌搜索，阅读文档，并观看了railscast，但我无法绕过这个。请帮忙。我在Ubuntu 13.04上运行最新的稳定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的关系。

但在现实生活中，User与Event或Lecturer或Student相关。 User可以是Student和Lecturer，但不能用于同一事件。 Lecturer或Student还不是我应用中的模型，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＃应该返回此特定活动的学生用户

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

User.first.events :as => :lecturer＃应返回特定用户的事件用户是讲师

我想也许has_many :through关联可能有用，但我很困惑。任何和所有指导赞赏。

此致

纳迪姆

Answer 1

您可以创建两个联接表events_students和events_lecturers，并设置这样的模型

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

UPD。

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

我正在将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

Rails Associations Riddle：用户，讲师，学生和活动

1 个答案: