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我正在尝试通过以下方式与 rails has_many 创建多对多关系：但是我需要使用不同的列创建关系，而不是使用模型主键（id）。这是我的模型（顺便说一句，我使用的是 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 的 has_many 关联适用于 Food 和 LangualFactorDescription。但是 has_many through: Food 和 LangualFactorDescription 之间的关联不起作用。这是我尝试访问 Food.LangualFactorDescriptions 时遇到的错误：

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)>'

我认为问题在于查询的这一部分ON "langual_factor_descriptions"."id" = "langual_factor_associations"."Factor_Code"。我认为设置 primary_key 和/或 foreign_key 选项可以解决这个问题，但事实并非如此。事实上，如果我从模型中删除它们并让它像

has_many :langual_factor_descriptions, through: :langual_factor_associations

rails 产生完全相同的查询，所以在我看来，设置这些选项没有任何作用。我在这里错过了什么吗？关于如何告诉 rails 不要寻找 langual_factor_descriptions.id 而是 langual_factor_descriptions.Factor_Code 的任何想法？

以下是我读过的关于这个主题的一些最相关的资源：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 不起作用（这几乎是我遇到的问题，但我不确定这是正确的解决方案）

Rails has_many 与多个键的关联

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

有许多替代主键和外键

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1 回答 1

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我想我解决了这个问题。这是代码：

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

请注意，我没有在 has_many through: 关联中使用 foreign_key 或 primary_key 选项，并且不需要self.primary_key.

此外，这里还有一些其他有用的链接对我有帮助：

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

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

尽管问题的解决是巧合，但我相信这些链接提供了相关信息。

于 2013-07-23T12:04:32.433 回答