Question

我有文档，其中一些是相关的，关系是对称的。也就是说，我尝试根据association和join table的HABTM说明对此关系进行建模。

我可以为两个Document实例d1.related_documents << d2。 d1.related_documents可以工作并返回相关文档，但d2.related_documents会返回一个空集。

我已声明表和模型如下：

文件表

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

  t.timestamps
end

加入表格

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

Answer 1

自我引用的habtm有点超出标准的Rails工具箱。您需要调整finder_sql或有两个关系：

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

如果需要将结果联合成一个SQL，则需要调整Finder-SQL，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} 
       )}

自引用Rails HABTM关联仅以一种方式工作

1 个答案: