MongoDB Aggregation Framework - How To Query For An Average

Question

How can I rewrite this MongoDB query using the Aggregation Framework to return the average price for the following Model in between the supplied date range:

Model

var PriceSchema = new Schema({
    price: {
        type: Number,
        required: true
    },
    date: {
        type: Date,
        required: true
    }
};

Query

exports.getPriceAverage = function(req, res, next) {
    var start       = moment.utc('03-01-2012').startOf('day');
    var end         = moment.utc('03-01-2012').endOf('month')

    // Aggregation Framework Query Here...
    Price.find({ date: { $lt: end, $gt: start }}, function(err, priceAverage) {
         // Return average price...
    });
};

WiredPrairie · Accepted Answer · 2014-03-30 12:38:04Z

2

You mention using aggregation, but you're using the find function which would return all results to the client.

Instead, you need to use aggregate with $avg:

Price.aggregate([
    { $match: { date: { $lt: end, $gt: start } } },
    { $group: { _id: null, avgPrice: { $avg: '$price' } } }

], function(err, results){
   // process the results (an array of JavaScript objects)
});

edited Mar 30, 2014 at 12:38

answered Mar 30, 2014 at 12:27

WiredPrairie

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