RubyOnRails / 从深度嵌套的关系模型构建完整的树

Question

具有以下自相关多对多设置：

class Item < ApplicationRecord
  has_many :joins, dependent: :destroy
  has_many :child_items, through: :joins
end

class Join < ApplicationRecord
  belongs_to :item
  belongs_to :child_item, class_name: 'Item'
end

重建完整树的 json 表示最直接的模式是什么？喜欢：

[
  {
    id: 1,
    child_items: [
      {
        id: 2,
        child_items: [
          {
            id: 3,
            child_items: etc… untils there are no more
          }
        ]
    ]
  }, {
    id: 4,
    child_items: { etc... }
  }, etc…
]

到目前为止，我有以下简单内容：

def render
  iterate(entrypoint_item)
end

def iterate(node)
  h = JSON.parse(node.to_json)
  h['child_items'] = []
  node.child_items.collect{ |child|
    h['child_items'] << iterate(child)
  }
  h.delete('child_items') if h['child_items'].length <= 0
  h
end

有没有更多的 ruby​​/rails 方式来完成这个？

Answer 1

这样的事情应该会给你一些启发：

class Item < ApplicationRecord
  has_many :joins, dependent: :destroy
  has_many :child_items, through: :joins

  def as_json_iterated
    options = {}
    chain_length.times { options[:include] = {child_items: options} }
    as_json(options)
  end

  def chain_length(counter = 0)
    return counter if child_items.empty?
    child_items.map { |item| item.chain_length(counter + 1) }.max
  end

end

这会导致：

Item.find(1).as_json_iterated
#=> {
#     "id"=>1, 
#     "child_items"=>[{
#       "id"=>2, 
#       "child_items"=>[{
#         "id"=>4, 
#         "child_items"=>[{
#           "id"=>7,  
#           "child_items"=>[]
#         }]
#       }, {
#         "id"=>5, 
#         "child_items"=>[]
#       }]
#     }, {
#       "id"=>3,  
#       "child_items"=>[{
#         "id"=>6,
#         "child_items"=>[]
#       }]
#     }]
#   }

请记住，此方法的 SQL 性能很差。

有关 #as_json 选项的更多信息，请参阅：ActiveModel::Serializers::JSON#as_json