Ruby on Rails的ActiveRecord的＆QUOT;的has_many：通过＆QUOT;唯一性验证 [英] Ruby on Rails ActiveRecord "has_many :through" uniqueness validation

问题描述

目前我通过插入每次检查的新的关系，如果它不存在：

 除非Relationship.exists（：entry_id =＆GT; entry.id，：tag_id =＆GT; tag.id）？
 

我

如何才能实现关系模型中这样的验证，因此它不会允许有相同的进入和标签之间的多个关系？

解决方案

 类关系＆LT;的ActiveRecord :: Base的
  belongs_to的：进入
  belongs_to的是：标签
  验证：tag_id，分别：独特性=＆GT; {：范围=＆GT; ：entry_id}
结束
 

Currently I insert a new relationship by everytime checking, if it doesn't exist:

unless Relationship.exists?(:entry_id => entry.id, :tag_id => tag.id)

How could I implement such validation inside the Relationship model, so that it wouldn't allow to have more than one relationship between the same entry and tag?

解决方案

class Relationship < ActiveRecord::Base
  belongs_to :entry
  belongs_to :tag
  validates :tag_id, :uniqueness => { :scope => :entry_id }
end

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