外 collection 上的匹配条件与 mongoDB 中的查找

Question

我有 3 collections

users: [
{_id: "aaa", name: "John", department: 1},
{_id: "bbb", name: "Charles", department: 1},
{_id: "ccc", name: "Jessy", department: 1"},
{_id: "ddd", name: "Tim", department: 2},
{_id: "eee", name: "Max", department: 2},
{_id: "fff", name: "Julia", department: 2},
{_id: "ggg", name: "Arnold", department: 3}
]

departments: [
{_id: 1, name: "press", society: "times"},
{_id: 2, name: "news", society: "times"},
{_id: 3, name: "infos", society: "herald"}
]

society: [
{name: "times", country: "England"},
{name: "herald", country: "USA"}
]

一个用户在一个部门工作，一个部门在一个社会。

我想做 2 个请求，第一个是让所有来自“时代”社会的用户，第二个是让所有来自“英格兰”国家的用户。

我为第一个尝试了这个请求：

db.users.aggregate([
{'$match': {'dept.society': "times"}
{
            '$lookup': {
                'from': "departments",
                'localField': "department",
                'foreignField': "_id",
                'as': "dept"
            }
        }])

但是因为条件是在国外collection（“部门”），好像不行。仅在本地 collection 条件下有效 ('department': 1)。我该怎么做，国家请求也是同样的问题吗？

Answer 1

两次查找即可完成

先获取society name times，再查找那两个集合

游乐场：https://mongoplayground.net/p/q-oCBjm-0hQ

db.society.aggregate([
  {
    "$match": {
      "name": "times"
    }
  },
  {
    "$lookup": {
      "from": "departments",
      "localField": "name",
      "foreignField": "society",
      "as": "dept_society"
    }
  },
  {
    "$lookup": {
      "from": "users",
      "localField": "dept_society._id",
      "foreignField": "department",
      "as": "user_dept"
    }
  }
])

Answer 2

有很多方法可以实现你的两个查询。我还看到您想从 users 集合开始聚合。

这是一种查询方式：

all users from the society "times"

db.users.aggregate([
  {
    "$lookup": {
      "from": "departments",
      "localField": "department",
      "foreignField": "_id",
      "pipeline": [
        {
          "$match": {
            "society": "times"  // input society
          }
        }
      ],
      "as": "deptLookup"
    }
  },
  { "$match": { "$expr": { "$gt": [ { "$size": "$deptLookup" }, 0 ] } } },
  { "$unset": "deptLookup" }
])

在 mongoplayground.net 上试用。

这是一种查询方式：

all users from the country "England"

db.users.aggregate([
  {
    "$lookup": {
      "from": "departments",
      "localField": "department",
      "foreignField": "_id",
      "pipeline": [
        {
          "$lookup": {
            "from": "society",
            "localField": "society",
            "foreignField": "name",
            "pipeline": [
              {
                "$match": {
                  "country": "England"  // input country
                }
              }
            ],
            "as": "socLookup"
          }
        },
        { "$match": { "$expr": { "$gt": [ { "$size": "$socLookup" }, 0 ] } } }
      ],
      "as": "deptSocLookup"
    }
  },
  { "$match": { "$expr": { "$gt": [ { "$size": "$deptSocLookup" }, 0 ] } } },
  { "$unset": "deptSocLookup" }
])

在 mongoplayground.net 上试用。

外 collection 上的匹配条件与 mongoDB 中的查找

match condition on on foreign collection with lookup in mongoDB

mongodb

pymongo