How get all objects from an array of Id's in mongoose with express nodejs-CodePudding

I'm developing a Chat application where I'm saving the conversation list in the DB like this;

Conversations Collection:

{ 
   members: [ "123", "456" ]
   ...rest
}

and User Collection:

{
   _id: ObjectId( "123" ), name: "anyone"
},
{
   _id: ObjectId( "456" ), name: "someone"
}

I want the result to be like:

{
   members: [
              {_id: ObjectId( "123" ), name: "anyone"},
              {_id: ObjectId( "456" ), name: someone"}
            ]
}

I know aggregation with lookup is the rescue but can't find a way how to fetch all ids from that member's array because in future it can be 20 to 30 ids. If it is a simple field then I'm able to fetch but with an array, I can't.

CodePudding user response：

You can use a normal .find() like this:

const members = [
    ObjectId('4ed3ede8844f0f351100000c'),
    ObjectId('4ed3f117a844e0471100000d'), 
    ObjectId('4ed3f18132f50c491100000e')
]

const docs = await model.find({
    '_id': { $in: members }
}).exec()

CodePudding user response：

You could use the following query to accomplish what you want. You'll need to use $lookup since you are wanting to gather data from a different collection then the one you are currently querying.

You can check out a live demo here

Database

db={
  "conversations": [
    {
      members: [
        123,
        456
      ]
    }
  ],
  "users": [
    {
      "_id": 123,
      "name": "foo"
    },
    {
      "_id": 456,
      "name": "bar"
    }
  ]
}

Query

db.conversations.aggregate([
  {
    "$lookup": {
      "from": "users",
      "localField": "members",
      "foreignField": "_id",
      "as": "members"
    }
  },
  {
    $project: {
      _id: 0,
      members: 1
    }
  }
])

Result

[
  {
    "members": [
      {
        "_id": 123,
        "name": "foo"
      },
      {
        "_id": 456,
        "name": "bar"
      }
    ]
  }
]