Question

i have a question about passing an arugment in MongoDB javascript to a map function.
Currently, what i had in mind is something like this:

var map = function(n) {
    if(this.x == n){
        emit(this.x);
    }
}
var reduce = function(key, values) {
    values.forEach(function(x) {
        //do something
    });
    return {nd:values};
}
db.smsdb.mapReduce(map(2), reduce, "collection")

But as i have tried to do this, the shell returns an error “not code”…so i’m guessing i’m not doing this the right way.
Does anyone have the right solution for this kind of problem, i would be more than glad to get it right.

Thanks

Answer 1

This line:

db.smsdb.mapReduce(map(2), reduce, "collection")

is calling map(2) with the result (undefined) being passed as the map function for mapReduce.

Instead do something like this:

db.smsdb.mapReduce(function(){ map.call(this, 2); }, reduce, "collection")

UPDATE

The above doesn’t work because the map function isn’t available in the scope the mapReduce map function is run. So you have to wrap it up into a single function that can generate the map function you need:

var mapper = function(n) {
    function map() {
        if(this.x == n){
            emit(this.x);
        }
    }
    return map;
};
db.smsdb.mapReduce(mapper(2), reduce, "collection");