我正在尝试使用Rails的has_many through:创建多对多关系,但是我需要使用不同的列创建关系,而不是使用模型的主键(id)。
这是我的模型(顺便说一句,我正在使用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
对于Food和LangualFactorDescription,has_many与LangualFactorAssociation的关联正常工作。但是Food和LangualFactorDescription之间的has_many through:关联不起作用。当我尝试访问Food.LangualFactorDescriptions时,会出现以下错误:
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)>'
我认为问题出在查询语句的这一部分 ON "langual_factor_descriptions"."id" = "langual_factor_associations"."Factor_Code"。 我曾以为设置primary_key和/或foreign_key选项可以解决这个问题,但实际上并没有。事实上,如果我从模型中删除它们,只剩下如下代码。
has_many :langual_factor_descriptions, through: :langual_factor_associations
Rails生成完全相同的查询,所以我觉得设置这些选项没有任何作用。我错过了什么吗?您有任何想法,可以告诉Rails不要查找langual_factor_descriptions.id而是langual_factor_descriptions.Factor_Code吗?
以下是我阅读过的与此主题最相关的资源之一: http://guides.rubyonrails.org/association_basics.html
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html
has_many :through在联接表上使用主键无法正常工作(这基本上是我遇到的问题,但我不确定这是否是正确的解决方案)
primary_key
告诉 ActiveRecord 哪个字段将用于连接另一个表。 - yxf