How to add fields from another collection in mongodb-CodePudding

I'm having two collections collection 'A' and 'B'

In collection 'A' I'm having fields:

Name, School, Class, Rank

In collection 'B' I'm having fields:

FatherName, MotherName, Location

How to add collection 'B' fields FatherName, MotherName, and Location to Collection 'A'

db.A.aggregate( [
   { $project: { _id: 0 } },
   { $merge : { into : "newCollection" } }
] )

This is not giving me derived result. Any better efficient result. Thank you.

CodePudding user response：

Every document has an _id ,

if you want _id = 1 merge _id = 1,

_id = 2 merge _id = 2

data

db={
  "users": [
    {
      "_id": 1,
      "Name": "almonds",
      "School": "C",
      "Class": "A",
      "Rank": 2
    }
  ],
  "datas": [
    {
      "_id": 1,
      "FatherName": "F",
      "MotherName": "M",
      "Location": "D"
    }
  ]
}

aggregate

db.users.aggregate([
  {
    "$lookup": {
      "from": "datas",
      "localField": "_id",
      "foreignField": "_id",
      "as": "docs"
    }
  }
])

result

[
  {
    "Class": "A",
    "Name": "almonds",
    "Rank": 2,
    "School": "C",
    "_id": 1,
    "docs": [
      {
        "FatherName": "F",
        "Location": "D",
        "MotherName": "M",
        "_id": 1
      }
    ]
  }
]

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