Mongodb 查找查找单个深度嵌套文档的多个集合

要继续我们的previous discussion强，一种 Select 是:

db.distributors.aggregate([
  {
    "$match": {
      "uid": "d1"
    }
  },
  {
    $lookup: {
      from: "fruits",
      localField: "children.children.children.children.child",
      foreignField: "uid",
      as: "fruits"
    }
  },
  {
    $lookup: {
      from: "tools",
      localField: "fruits.variants.tools",
      foreignField: "uid",
      as: "tools"
    }
  },
  {
    $set: {
      tools: "$$REMOVE",
      fruits: {
        $map: {
          input: "$fruits",
          as: "f",
          in: {
            $mergeObjects: [
              "$$f",
              {
                variants: {
                  $map: {
                    input: "$$f.variants",
                    as: "v",
                    in: {
                      $mergeObjects: [
                        "$$v",
                        {
                          tools: {
                            $map: {
                              input: "$$v.tools",
                              as: "t",
                              in: {
                                $arrayElemAt: [
                                  "$tools",
                                  {
                                    $indexOfArray: [
                                      "$tools.uid",
                                      "$$t"
                                    ]
                                  }
                                ]
                              }
                            }
                          }
                        }
                      ]
                    }
                  }
                }
              }
            ]
          }
        }
      }
    }
  },
  {
    $project: {
      countriesA: {
        $map: {
          input: "$children",
          as: "country",
          in: {
            $mergeObjects: [
              "$$country",
              {
                children: {
                  $map: {
                    input: "$$country.children",
                    as: "city",
                    in: {
                      $mergeObjects: [
                        "$$city",
                        {
                          children: {
                            $map: {
                              input: "$$city.children",
                              as: "district",
                              in: {
                                $mergeObjects: [
                                  "$$district",
                                  {
                                    children: {
                                      $map: {
                                        input: "$$district.children",
                                        in: {
                                          $arrayElemAt: [
                                            "$fruits",
                                            {
                                              $indexOfArray: [
                                                "$fruits.uid",
                                                "$$this"
                                              ]
                                            }
                                          ]
                                        }
                                      }
                                    }
                                  }
                                ]
                              }
                            }
                          }
                        }
                      ]
                    }
                  }
                }
              }
            ]
          }
        }
      }
    }
  }
])

看看它在mongoDB playground号公路上是如何工作的