带条件的mongodb聚合多重查找

Question

我有三个收藏品。

db.a.insert([
  { "_id" : ObjectId("5b56989172ebcb11105e8f41"), "db_type":b, "number" : 1},
  { "_id" : ObjectId("5b56989172ebcb11105e8f42"), "db_type":c, "number" : 2},
])

db.b.insert([
  { "_id" : ObjectId("5b56989172ebcb11105e8f43"), "number" : 1, "value" : "111"},
])

db.c.insert([
  { "_id" : ObjectId("5b56989172ebcb11105e8f44"), "number" : 2, "value" : "222"},
])

我想做一个查找查询，根据db_type从每个集合中获取值。

在这种情况下我该怎么办？

结果：

{ "_id" : ObjectId("5b56989172ebcb11105e8f41"), "db_type" : b, "number" : 1, "value" : "111"}
{ "_id" : ObjectId("5b56989172ebcb11105e8f42"), "db_type" : c, "number" : 2, "value" : "222"}

堵塞部分..。

db.getCollection('a').aggregate([
    {
        "$lookup":{
            "from":         "b" or "c", // I want to give condition here.
            "localField":   "number",
            "foreignField": "number",
            "as":           "result"
        }
    },
])

Answer 1

对于您的情况，您只有2种情况可以查找-- b和c。您可以简单地进行两个单独的查找，并使用$setUnion将结果分组。

db.a.aggregate([
  {
    "$lookup": {
      "from": "b",
      "let": {
        db_type: "$db_type",
        number: "$number"
      },
      "pipeline": [
        {
          $match: {
            $expr: {
              $and: [
                {
                  $eq: [
                    "$$db_type",
                    "b"
                  ]
                },
                {
                  $eq: [
                    "$$number",
                    "$number"
                  ]
                }
              ]
            }
          }
        }
      ],
      "as": "bLookup"
    }
  },
  {
    "$lookup": {
      "from": "c",
      "let": {
        db_type: "$db_type",
        number: "$number"
      },
      "pipeline": [
        {
          $match: {
            $expr: {
              $and: [
                {
                  $eq: [
                    "$$db_type",
                    "c"
                  ]
                },
                {
                  $eq: [
                    "$$number",
                    "$number"
                  ]
                }
              ]
            }
          }
        }
      ],
      "as": "cLookup"
    }
  },
  {
    "$addFields": {
      "allLookup": {
        "$setUnion": [
          "$bLookup",
          "$cLookup"
        ]
      }
    }
  }
])

这是供您参考的蒙戈游乐场。