ruby-on-rails - 从 rails 自引用关联生成嵌套层次结构响应

Question

我有一个 self 参照模型，

class Hierarchy < ActiveRecord::Base
  has_many :children, :class_name => "Hierarchy", :foreign_key => 'parent_id'

  def descendents
    children.map do |child|
      [child] + child.descendents
    end
  end
end

如何从这样的模型“层次结构”构建层次结构树，

{
  "hierarchies": [
    {
      "level": 1, "id": 14951, "name": "EQUIPMENT", "parent_id": null,
      "children": [
        {
          "level": 2, "id": 15040, "name": "BASKETBALL", "parent_id": 14951,
          "children": [
            {
              "level": 3, "id": 15154, "name": "EYEWEAR", "parent_id": 15040,
              "children": [
                {
                  "level": 4, "id": 16617, "name": "OPHTHALMIC", "parent_id": 15154,
                  "children": []
                }
              ]
            },
            {
              "level": 3, "id": 16417, "name": "OTHER", "parent_id": 15040, "children": []
            }
          ]
        }
      ]
    }
  ]
}

“Herarchy”模型的descendents 方法可以从Herarchy 模型迭代和检索数据，直到最后一层。

例子:

  render :json => { :hierarchies => [root_hierarchy, root_hierarchy.descendents]}

它返回所有级别，

{
  "hierarchies": [
    {
      "level": 1, "id": 14951, "name": "EQUIPMENT", "parent_id": null
    },
    [
      [
        {
          "level": 2, "id": 15040, "name": "BASKETBALL", "parent_id": 14951
        },
        [
          {
            "level": 3, "id": 15154, "name": "EYEWEAR", "parent_id": 15040
          },
          [
            {
              "level": 4, "id": 16617, "name": "OPHTHALMIC", "parent_id": 15154
            }
          ]
        ],
        [
          {
            "level": 3, "id": 16417, "name": "OTHER", "parent_id": 15040
          }
        ]
      ]
    ]
  ]
}

问题是我无法在每次迭代中附加其关联的子项。我尝试了 as_json、includes 方法将子项附加到其父对象中，但没有成功。

Answer 1

我以前遇到过同样的问题。我建议你看看 closure_tree .它添加了一些非常有用的方法来操作分层数据。它有一种只需要 1 个 SELECT 查询就可以获取后代的方法。您当前使用邻接列表的实现很简单，但它需要对每个后代进行一次查询，并且很快就会变得低效。