$eerst in mongodb

Je moet $first . gebruiken aggregatie-operator om het eerste document te retourneren na toepassing van de $group podium.

ScoreBoardModel.aggregate([
  { "$match": { challenge_id: mongoose.Types.ObjectId(req.body.challenge_id) } },
  { "$lookup": {
    "from": "appusers",
    "let": { "user_id": "$user_id" },
    "pipeline": [{ "$match": { "$expr": { "$eq": [ "$_id", "$$user_id" ] } } }],
    "as": "user"
  }},
  { "$group": {
    "_id": "$user_id",
    "value": { "$sum": "$value" },
    "appusers": { "$first": "$user" },
  }}
])