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自引用Rails HABTM关联只能单向工作

rails-activerecord ruby-on-rails

Mr. Tao · 技术社区 · 7 年前

我有文件,其中一些是相关的 关系是对称的 .也就是说,我试图根据HABTM的指示为两者建立这种关系的模型 association 和 join table 。

我能做到 d1.related_documents << d2 对于文档的两个实例。 d1.related_documents 工作并返回相关文件,但 d2.related_documents 返回一个空集。

我已经声明了如下表和模型:

文档表

create_table :documents do |t|
  t.string :matter
  t.string :url_id, unique: true
  t.text :body

  t.timestamps
end

联接表

create_join_table :documents, :documents, table_name: :related_documents, id: false do |t|
  t.references :referent, foreign_key: { to_table: :documents, 
                                         primary_key: :url_id }, index: true
  t.references :reference, foreign_key: { to_table: :documents, 
                                          primary_key: :url_id }, index: true
  end
end

模型

has_and_belongs_to_many :related_documents, join_table: :related_documents, 
                                            class_name: "Document", 
                                            foreign_key: :referent_id, 
                                            association_foreign_key: :reference_id

1 回复 | 直到 7 年前

stwienert 7 年前

自引用habtm在标准Rails工具箱之外有一点。您需要调整finder\u sql或有2个关系:

has_and_belongs_to_many :related_documents, join_table: :related_documents, 
                                            class_name: "Document", 
                                            foreign_key: :referent_id, 
                                            association_foreign_key: :reference_id
has_and_belongs_to_many :referenced_documents, join_table: :related_documents, 
                                            class_name: "Document", 
                                            foreign_key: :reference_id, 
                                            association_foreign_key: :referent_id

如果需要将结果合并到一个SQL中,则需要调整Finder SQL,请参见例如。 https://gist.github.com/srpouyet/4121517

has_and_belongs_to_many :related_documents,
                          class_name: 'Document',
                          join_table: :related_documents,
                          foreign_key: :reference_id,
                          association_foreign_key: :referent_id,
                          uniq: true,
                          finder_sql: proc { 
     %(SELECT DISTINCT "documents".* FROM "documents"
       INNER JOIN "related_documents" 
         ON "documents"."id" = "related_documents"."referent_id"
       WHERE "related_documents"."reference_id" =  #{id}
       UNION
       SELECT DISTINCT "documents".* FROM "documents"
       INNER JOIN "related_documents" 
         ON "documents"."id" = "related_documents"."reference_id"
       WHERE "related_documents"."referent_id" =  #{id} 
       )}