How can I get only a single value back in MongoDB (Pymongo)

Question

This is the document I have right now:

{
    _id: ObjectId("62464e3e75c6d843a338993b"),
    Name: 'The Team',
    Members: [
      { User: Long("699724278526580847"), Rank: 3 },
      { User: Long("937398909418999808"), Rank: 4 },
      { User: Long("829765893287562113"), Rank: 1 },
      { User: Long("090119389582045756"), Rank: 1 },
      { User: Long("772474927459011034"), Rank: 1 },
    ]
}

I want to get the "Rank" Value of a user which is chosen through an input, for this example let's say the person executing the command chose the user with the ID "699724278526580847", how would I query and get just the rank of that user returned? Is it possible in pymongo to just get the integer value of that user's rank?

Answer 1

Maybe something like this in mongo that you can convert easily to python:

db.collection.aggregate([
 {
  $match: {
     Name: "The Team" , "Members.User": NumberLong("699724278526580847")
  }
 },
{
"$addFields": {
  "Members": {
    "$filter": {
      "input": "$Members",
      "as": "m",
      "cond": {
        $eq: [
          "$$m.User",
          NumberLong("699724278526580847")
        ]
      }
    }
   }
  }
  },
  {
   $unwind: "$Members"
  },
  {
   "$project": {
     Rank: "$Members.Rank",
     _id: 0
  }
 }
])

Explained:

1. Match the Member & The Team
2. Filter only the Member by User from the array
3. Unwind the array to convert to object
4. Project only the Rank field

playground