Question

When using MapReduce, each resulting document is structured like this

{
    "_id"   : 123
    "value" : 99.95
}

Is there a way to specify other field names? E.g. _id -> sku, value -> price.

MapReduce:

db.runCommand({
    mapreduce : "myCollection",
    map : function () {
        emit( this.sku, this.price );
    },
    reduce : function (key, values) {
        var result = Number.MAX_VALUE;
        values.forEach(function(value) {
            if (result > value) {
                result = value;
            }
        });
        return result;
    },
    out : { replace : "myReduceTest" }
});

Answer 1

I don’t believe there is and I wonder why you need to change them? With map/reduce you can return objects for both “_id” and “value” which can have fields with whatever names you wish. See examples at http://www.mongodb.org/display/DOCS/MapReduce