Mongo DB find all records with highest value depending on a key field

Question

I would like to get for each user in my collection the comment of the record with the highest value.

//myCol
[
    {\'user\' : 1, \'value\':20, \"comment\":          


        

Answer 1

You can even do with two stages only

db.collection.aggregate([
  { "$group": {
    "_id": "$user",
    "doc": {
      "$max": {
        "value": "$value",
        "user": "$user",
        "comment": "$comment",
        "date": "$date"
      }
    }
  }},
  { "$replaceRoot": { "newRoot": "$doc" }}
])

$max always takes the maximum value of the first expression which is passed inside the object. Here it is value.

Answer 2

It does, but the approach is slightly different:

db.myCol.aggregate([
    {$sort: {value:-1}},
    {$group:{
        _id: "$user",
        doc: {$first: "$$ROOT"}
    }},
    {$replaceRoot: {newRoot: "$doc"} }
])

Answer 3

You can $sort your documents by value before applying $group with $first

db.myCol.aggregate([
    { 
        $sort: { value: -1 }
    },
    {
        $group: {
            _id: "$user",
            value: { $first: "$value" },
            comment: { $first: "$comment" },
            date: { $first: "$date" }
        }
    },
    {
        $sort: { _id: 1 }
    },
    {
        $project: {
            user: "$_id",
            _id: 0,
            value: 1,
            comment: 1,
            date: 1
        }
    }
])