如果不存在 has_many 个实例，则删除 belongs_to 个实例

Question

对于这些模型：

class Folder < ApplicationRecord
   has_many :documents_folders_requests, dependent::destroy 
end

class DocumentsFoldersRequest < ApplicationRecord
  belongs_to :folder
  belongs_to :child_folder, class_name: "Folder", optional: true
end

如果 DocumentsFoldersRequest 记录被删除，并且不存在使用该 Folder 记录作为 folder_id 或 child_folder_id 的其他 documents_folders_request 记录，有没有办法自动删除Folder记录？此时它会被认为是“孤立的”——因为它在任何关联中都找不到，并且没有 folders_controller#index 可以在任何地方显示所有文件夹记录。这可以从模型中完成吗？

示例：

dfr = DocumentsFoldersRequest.find_by(document_id: 123)

folder_id = dfr.folder.id 
=> [1]

dfr.destroy_all
=> true

# is there a better way to write the following: 
if DocumentsFoldersRequest.where(folder: folder_id).nil? && DocumentsFoldersRequest.where(child_folder: folder_id).nil?
  folder = Folder.find(folder_id)
  folder.destroy
end

Answer 1

有几个选项。主要归结为您何时要执行此操作。

我建议你在删除 DocumentsFoldersRequest

时这样做

任何时候删除一个，检查父 folder 和 child_folder:

class DocumentsFoldersRequest < ApplicationRecord
  after_destroy :check_for_orphaned_folder

  def check_for_orphaned_folder
    folder.destroy if folder.documents_folders_requests.none?
    child_folder.destroy if child_folder.documents_folders_requests.none?
  end

end

如果不存在 has_many 个实例，则删除 belongs_to 个实例

delete belongs_to instance if no instances of has_many exist

ruby-on-rails

rails-activerecord

ruby-on-rails-5