自引用 Rails HABTM 关联仅单向工作

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 HABTM 指令对关联和连接表对这种关系进行建模。

我可以对文档的两个实例执行d1.related_documents << d2操作。d1.related_documents工作并返回相关文档，但d2.related_documents返回一个空集。

我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
  

• 连接表

  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
  

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 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

如果您需要将结果合并为一个 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} 
)}