Rails has_many：通过与：primary_key

Question

我想创建一个多对多的关系与轨道has_many通过：但不是使用模型主键（id）我需要使用不同的列创建关系。 这里是我的模型（顺便说一句，我使用Rails 4）：

class Food < ActiveRecord::Base 
    validates :NDB_No, uniqueness: true 
    validates :NDB_No, :FdGrp_Cd, :Long_Desc, :Shrt_Desc, presence: true 

    has_many :langual_factor_associations, primary_key: 'NDB_No', foreign_key: 'NDB_No' 
    has_many :langual_factor_descriptions, through: :langual_factor_associations, primary_key: 'NDB_No', foreign_key: 'NDB_No' 
end 

class LangualFactorAssociation < ActiveRecord::Base 
    validates :NDB_No, :Factor_Code, presence: true 

    belongs_to :food, foreign_key: 'NDB_No' 
    belongs_to :langual_factor_description, foreign_key: 'Factor_Code' 
end 

class LangualFactorDescription < ActiveRecord::Base 
    validates :Factor_Code, uniqueness: true 
    validates :Factor_Code, :Description, presence: true 

    has_many :langual_factor_associations, primary_key: 'Factor_Code', foreign_key: 'Factor_Code' 
    has_many :foods, through: :langual_factor_associations, primary_key: 'Factor_Code', foreign_key: 'Factor_Code' 

end 

与LangualFactorAssociation该协会的has_many工作正常用于食品和LangualFactorDescription。但has_many通过：Food和LangualFactorDescription之间的关联不起作用。这里是我的错误，当我尝试访问Food.LangualFactorDescriptions：

Food::should create the proper relations to the LangualFactorDescription 
      model#test_0002_must create the proper associations: 
ActiveRecord::StatementInvalid: PG::Error: ERROR: operator does not exist: integer = character varying 
LINE 1: ...sociations" ON "langual_factor_descriptions"."id" = "langual... 
                  ^
HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts. 
: SELECT "langual_factor_descriptions".* FROM "langual_factor_descriptions" INNER JOIN "langual_factor_associations" ON "langual_factor_descriptions"."id" = "langual_factor_associations"."Factor_Code" WHERE "langual_factor_associations"."NDB_No" = $1 ORDER BY "langual_factor_descriptions"."id" ASC LIMIT 1 
    test/models/food_test.rb:172:in `block (3 levels) in <top (required)>' 

我认为这个问题是查询的这部分ON“langual_factor_descriptions”，“ID” =“langual_factor_associations”“Factor_Code”。 。我认为设置primary_key和/或foreign_key选项会解决这个问题，但事实并非如此。事实上，如果我从模型中删除这些，只是把它像

has_many :langual_factor_descriptions, through: :langual_factor_associations 

导轨产生完全相同的查询，所以在我看来，设置这些选项不做任何事。我在这里错过了什么吗？任何想法如何我可以告诉轨道不寻找langual_factor_descriptions.id而是langual_factor_descriptions.Factor_Code？

下面是一些最相关的资源，我看了一下这个话题： http://guides.rubyonrails.org/association_basics.html

http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

has_many :through with :primary_key on join table not working（其实这就是我有问题，但我不知道这是正确的解决方案）

Rails has_many association with multiple keys

https://www.ruby-forum.com/topic/139765

Has Many Through Alternative Primary and Foreign Keys

Answer 1

我想我解决了这个问题。下面是代码：我没有通过使用foreign_key也不primary_key选项中的has_many

class Food < ActiveRecord::Base 
    validates :NDB_No, uniqueness: true 
    validates :NDB_No, :FdGrp_Cd, :Long_Desc, :Shrt_Desc, presence: true 

    has_many :langual_factor_associations, primary_key: 'NDB_No', foreign_key: 'NDB_No' 
    has_many :langual_factors, through: :langual_factor_associations  
end 

class LangualFactorAssociation < ActiveRecord::Base 
    validates :NDB_No, :Factor_Code, presence: true 

    belongs_to :food, primary_key: 'NDB_No', foreign_key: 'NDB_No' 
    belongs_to :langual_factor, primary_key: 'Factor_Code', foreign_key: 'Factor_Code' 
end 

class LangualFactor < ActiveRecord::Base 
    validates :Factor_Code, uniqueness: true 
    validates :Factor_Code, :Description, presence: true 

    has_many :langual_factor_associations, primary_key: 'Factor_Code', foreign_key: 'Factor_Code' 
    has_many :foods, through: :langual_factor_associations  
end 

注意：协会，没有必要self.primary_key。

另外，这里有一些其他有用的链接，帮助我：

http://railsforum.com/viewtopic.php?id=36186

http://guides.rubyonrails.org/v2.3.11/active_record_querying.html

即使解决问题的办法来巧合，我相信那些链接提供相关信息。