How to aggregate distinct array field in Mongodb

Question

I have this schema

const GroupSchema = new Schema({
  id: { type: String },
  users: [{ type: Number }],
  status: { type: Boolean }
},
  {
    timestamps: true
  });

I try to aggregate distinct users value sorted by created date. Example

 {
    "users": [1111, 2222],
    "createdAt": {
        "$date": "2020-09-30T10:51:33.058Z"
    }
}
    {
        "users": [1111, 2222],
        "createdAt": {
            "$date": "2020-09-29T10:51:33.058Z"
        }
    }

I try with :

Group.aggregate([
        { "$sort": { "createdAt": -1 } },
        { $group : { _id : "$users" }}, //, created : { $last : "created" }
        { $match : { users : {$in : [1111] }  }}
    ])

I expect

 {
"users": [1111, 2222],
"createdAt": {
    "$date": "2020-09-30T10:51:33.058Z"
}
}

how can i solve? Thanks.

Answer 1

You can try,

• $match your condition
• $sort by createdAt date
• $group by users array and get latest document in latestDoc
• $replaceWith to replace latestDoc in root

db.collection.aggregate([
  { $match: { users: { $in: [1111] } } },
  { $sort: { createdAt: -1 } },
  {
    $group: {
      _id: "$users",
      latestDoc: { $first: "$$ROOT" }
    }
  },
  { $replaceWith: "$latestDoc" }
])

Playground