Rails has_many：通過與：primary_key

Question

我想創建一個多對多的關係與軌道has_many通過：但不是使用模型主鍵（id）我需要使用不同的列創建關係。 這裏是我的模型（順便說一句，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 

與LangualFactorAssociation該協會的has_many工作正常用於食品和LangualFactorDescription。但has_many通過：Food和LangualFactorDescription之間的關聯不起作用。這裏是我的錯誤，當我嘗試訪問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)>' 

我認爲這個問題是查詢的這部分ON「langual_factor_descriptions」，「ID」 =「langual_factor_associations」「Factor_Code」。 。我認爲設置primary_key和/或foreign_key選項會解決這個問題，但事實並非如此。事實上，如果我從模型中刪除這些，只是把它像

has_many :langual_factor_descriptions, through: :langual_factor_associations 

導軌產生完全相同的查詢，所以在我看來，設置這些選項不做任何事。我在這裏錯過了什麼嗎？任何想法如何我可以告訴軌道不尋找langual_factor_descriptions.id而是langual_factor_descriptions.Factor_Code？

下面是一些最相關的資源，我看了一下這個話題： 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（其實這就是我有問題，但我不知道這是正確的解決方案）

Rails has_many association with multiple keys

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

Has Many Through Alternative Primary and Foreign Keys

Answer 1

我想我解決了這個問題。下面是代碼：我沒有通過使用foreign_key也不primary_key選項中的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：協會，沒有必要self.primary_key。

另外，這裏有一些其他有用的鏈接，幫助我：

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

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

即使解決問題的辦法來巧合，我相信那些鏈接提供相關信息。