Mongodb 如何在两个级别上进行聚合并保留文档？

这是我用来处理Elasticsearch的，但我找不到如何处理MongoDB

以下是一组动物：

[
  { kind: "Dog", owner: "John", name: "Max" },
  { kind: "Dog", owner: "John", name: "Buddy" },
  { kind: "Dog", owner: "John", name: "Cooper" },
  { kind: "Cat", owner: "John", name: "Charlie" },
  { kind: "Dog", owner: "Peter", name: "Jack" },
]

以下是我期待的结果：

{
  Dog: {
    John: [
      { kind: "Dog", owner: "John", name: "Max" },
      { kind: "Dog", owner: "John", name: "Buddy" },
      { kind: "Dog", owner: "John", name: "Cooper" },
    ],
    Peter: [
      { kind: "Dog", owner: "Peter", name: "Jack" },
    ]
  }
  Cat: {
    John: [
      { kind: "Cat", owner: "John", name: "Charlie" }
    ]
  }
}

---

有什么办法吗？我已经用

$group

和

$push

尝试了一些聚合，但我无法构建这个“嵌套”级别的动物/所有者/文档，您可以在3.6中使用下面的聚合

嵌套数组结构

db.colname.aggregate([
  {"$group":{"_id":{"kind":"$kind","owner":"$owner"},"docs":{"$push":"$$ROOT"}}},
  {"$group":{"_id":"$_id.kind","ownerbykind":{"$push":{"owner":"$_id.owner","docs":"$docs"}}}}
])

或

使用

$mergeObjects

和

$arrayToObject

生成所需的结构

db.colname.aggregate([
  {"$group":{"_id":{"kind":"$kind","owner":"$owner"},"a":{"$push":"$$ROOT"}}},
  {"$group":{"_id":"$_id.kind","b":{"$mergeObjects":{"$arrayToObject":[[["$_id.owner","$a"]]]}}}},
  {"$group":{"_id":null,"c":{"$mergeObjects":{"$arrayToObject":[[["$_id","$b"]]]}}}},
  {"$replaceRoot":{"newRoot":"$c"}}
])

---

谢谢你救了我一天！第二个查询不适用于我的真实案例，因为

owner

et

kind

是

objectid

而不是string（

$arrayToObject

抛出一个错误），但是第一个查询成功了！