use mongodb mapreduce to update document example

mongodb mapreduce

var m = function(){
    emit(this._id,this)
}

var r = function(k, value) {
    // here is the process of update data
    t = value.running_param.targets;
    for (var i = 0; i < t.length; i++) {
        var tmp = t[i].split("/")[1];
        if (tmp.indexOf(".") == -1) {
            if (tmp[0] == 6) {
                t[i] += ".SH"
            } else {
                t[i] += ".SZ"
            }
        }
    }
    value.running_param.targets = t;
    // note: return value must be identical to the type of emit value
    return value;
}
// reduce func is defined as function(k,v){}, because it won't be executed,
// data updating func is defined in finalizer
db.collection.mapReduce(m, function(k,v){}, {finalizer:r, out:"out"})
// after mapReduce func, the result is stored in "out" collection with the format of {"_id":ObjectId("ssss","value":{"ss":"bb"}}
// then we can use the following command to update it to original
db.out.find().forEach(function(item){db.out.update({_id:item._id}, item.value)})