Question

After trying this solution and getting one step further i have another question regarding mongodb.

My question is:

How can i sort the output of:

doc = {_id : 16, days : { 1 : 123, 2 : 129, 3 : 140, 4 : 56, 5 : 57, 6 : 69, 7 : 80 }};
db.so.insert(doc);

map = function() {
  emit(this._id, this.days["1"]);
  emit(this._id, this.days["3"]); 
  emit(this._id, this.days["7"]); 
}

reduce = function (k, vals) {
  var sum = 0;
  vals.forEach(function (v) {sum += v;});
  return sum;
}

res = db.so.mapReduce(map, reduce, {out : {inline : 1}});
res.find();

The Output is like this:

"results" : [
    {
            "_id" : 16,
            "value" : 225
    },
    {
            "_id" : 33,
            "value" : 230
    },
    {
            "_id" : 302,
            "value" : 274
    }

]

Now i want to sort the result with:

res.find().sort({ "results.value":-1 });

which results in this error:

Sat Mar 31 01:15:45 TypeError: res.find().sort({'results.value':-1}) is not a function (shell):1

Does anybody can help me ?

Answer 1

Here’s an example of the same query using the MongoDB 2.2 Aggregation Framework:

db.so.aggregate(
  { $project : {
     '_id' : 1,
     'value' : { $add : ["$days.1","$days.3","$days.7"] },
  }},
  { $sort: { 'value': -1 }}
)

.. and the output:

{
    "result" : [
        {
            "_id" : 302,
            "value" : 274
        },
        {
            "_id" : 33,
            "value" : 230
        },
        {
            "_id" : 16,
            "value" : 225
        }
    ],
    "ok" : 1
}