CODEWITHSUNDEEP
javascriptmongodbmapreduce
Gasim
Gasim

Reputation: 7981

How can I use a variable inside MapReduce?

I have the following script in MapReduce:

splitAndGroupServices = function(members) {
    var mapFn = function() {
       for(var j in this.services) {
         var service = this.services[j];
         if(service.member_id in members)
             emit(service.member_id, service);
       }
     }

     var reduceFn = ...; 
     var finalizeFn = ...;
     db.items.mapReduce(mapFn, reduceFn, {out: {inline:1}, finalize: finalizeFn});
}

When I call:

db.loadServerScripts();
splitAndGroupServices({b1: 0, b2: 1});

I keep getting error:

"errmsg" : "exception: ReferenceError: members is not defined near 'ber_id in members) {             emit(ser'  (line 4)",

How can I pass the outer function variable into an inner function variable? In JS it is actually possible but Mongo doesn't like it.

Upvotes: 0

Views: 35

Answers (1)

Blakes Seven
Blakes Seven

Reputation: 50416

The mapReduce command supports a "scope" which is shared across mapper, reducer and finalize stages:

db.items.mapReduce(
    mapFn,
    reduceFn, 
   { 
       "scope": { "members": members },
       "out": { "inline": 1 },
       "finalize": finalizeFn
   }
)

This is treated as a "global" for the process and any modifications are carried into the next stage or similarly available in that stage. It is a standard way of "passing variables" for use in any of the stage functions.

Upvotes: 1

Related Questions