RoR定义两个模型之间的有意义的关系

Question

我想定义一个rails项目中的多对多关系。如何给个人关系提供不同的意义？

+------------+  has many  +-------------+ 
|   | ---------------------> |    | 
| person |      | project | 
|   | <--------------------- |    | 
+------------+  has many  +-------------+ 

这种模式是一个好的开始，但不足以实现我的目标。一个人应该能够在一个项目中扮演不同的角色。例如在电影中还有演员，制片人，特技人，...

溶液应...

• 提供了一种简单的方法来定义新类型的关系（“角色”）
• 纳入轨道在一个不错的方式
• 是尽可能快地

什么是最好的选择吗？

Answer 1

处理这个问题的最好方法是创建一个丰富的连接表。

即：

 | has many => |  | <= has many | 
Person |    | Credit |    | Movie 
     | <= belongs to |  | belongs to => | 

哪里人与电影不从最初的例子有太大变化。 Credit包含的字段不仅仅是person_id和movie_id。 Credit的额外字段是角色和字符。

然后它只是一个有很多通过关系。不过，我们可以添加额外的关联来获得更多细节。保持与电影的例子：

class Person < ActiveRecord::Base 
    has_many :credits 
    has_many :movies, :through => :credits, :unique => true 
    has_many :acting_credits, :class_name => "Credit", 
    :condition => "role = 'Actor'" 
    has_many :acting_projects, :class_name => "Movie", 
    :through => :acting_credits 
    has_many :writing_credits, :class_name => "Credit", 
    :condition => "role = 'Writer'" 
    has_many :writing_projects, :class_name => "Movie", 
    :through => :writing_credits 

end 

class Credit < ActiveRecord::Base 
    belongs_to :person 
    belongs_to :movie 
end 

class Movie < ActiveRecord::Base 
    has_many :credits 
    has_many :people, :through => :credits, :unique => true 
    has_many :acting_credits, :class_name => "Credit", 
    :condition => "role = 'Actor'" 
    has_many :actors, :class_name => "Person", :through => :acting_credits 
    has_many :writing_credits, :class_name => "Credit", 
    :condition => "role = 'Writer'" 
    has_many :writers, :class_name => "Person", :through => :writing_credits 
end 

与所有那些额外的关联。以下每一项只有一个SQL查询：

@movie.actors # => People who acted in @movie 
@movie.writers # => People who wrote the script for @movie 

@person.movies # => All Movies @person was involved with 
@person.acting_projects # => All Movies that @person acted in 

Answer 2

人，项目和角色之间的关系应该是一个自己的表。创建一个具有人员，项目和该人员在该项目中的角色的作业类。然后人has_many :projects, :through => :assignments。