Mongo DB中的嵌套查询

Question

Here's my schema:

var playerScheme = new Schema({
    _id:String,
    score:Number
    }

Im trying to get the rank of each player by counting the number of users with more points than the user in question, say user X. I get passed the user id of x in the res parameter. I use the following query but cant figure out how to nest another find query after $gt to get the score for player x.

This is my code in node using Mongoose:

exports.getRankForUser = function(req,res) {

  var userId = ObjectId(req.body.userId); 
  var rank;

  playerModel.player.count({"score" :{$gt: GET SCORE FOR USERID QUERY}})
    .exec(function(err,result)
    {
      if(err) {
        res.send(err ,500);
      } else {
        res.send(result,200);
      }
    }
);

}

Answer 1

First, you must get the user X information. Once you have that information, you can perform a nested count query inside the first callback, using the obtained user X info as follows:

exports.getRankForUser = function(req,res) {

  var userId = ObjectId(req.body.userId); 
  var rank;

  playerModel.player.findById(userId, function(err, user){
      if(err){
          res.send(err ,500);
      }else if (!user){
          res.send('The requested user does not exist' ,404);
      }else{
          //At this point, you have the user X info in the var "user". 
          //Just query the count with a nested query
          playerModel.player.count({score: {$gt: user.score}})
          .exec(function(err, result){
              if(err) {
                  res.send(err ,500);
              } else {
                  //Here you are returning the number of users that 
                  //has a score value higher than the user X score.
                  res.send(result,200);
              }
          });
      }
  });

}