Ruby on Rails的多对多验证

Question

我：

scaffold attendance event:references user:references attendance_rate:references 
scaffold user name email 
scaffold event start_time end_time 
scaffold attendance_rate rate:integer #)[1 or 0], i do not want to use boolean) 

协会：

event has_many :attendances 
attendance belongs_to :event 

user has_many :attendances 
attendance belongs_to :user 

问题：我怎么能允许同一个用户 “参加” 同一事件只有一次？

Attendance.rb：

class Attendance < ActiveRecord::Base 
    belongs_to :user 
    belongs_to :attendance_rate 
    belongs_to :event 
    validates :user_id, :attendance_rate_id, presence: true 
    validates_uniqueness_of :event_id, :scope => [:user_id] 
end 

注：上座率在事件嵌套形式创作。

Answer 1

我会用uniqueness验证与scope选项。这将是类似的，

validates_uniqueness_of :event_id, :scope => [:user_id]在Attendance模型。