Meteor MapReduce Package Error: A method named is already defined

Question

Trying to use the monbro:mongodb-mapreduce-aggregation to run a super simple mapReduce function. While it works great the first time around, subsequent calls I get the following error:

I20150608-11:11:05.294(-4)? Exception while invoking method 'exportDonations' Error: A method named '/donation_totals_by_donor/insert' is already defined
I20150608-11:11:05.294(-4)?     at packages/ddp/livedata_server.js:1461:1
I20150608-11:11:05.294(-4)?     at Function._.each._.forEach (packages/underscore/underscore.js:113:1)
I20150608-11:11:05.294(-4)?     at [object Object]._.extend.methods (packages/ddp/livedata_server.js:1459:1)
I20150608-11:11:05.294(-4)?     at [object Object].Mongo.Collection._defineMutationMethods (packages/mongo/collection.js:904:1)
I20150608-11:11:05.294(-4)?     at new Mongo.Collection (packages/mongo/collection.js:209:1)
I20150608-11:11:05.295(-4)?     at [object Object].ns.Collection (packages/matb33:collection-hooks/collection-hooks.js:190:1)
I20150608-11:11:05.295(-4)?     at [object Object].Meteor.methods.exportDonations (app/server/index.js:44:19)
I20150608-11:11:05.295(-4)?     at [object Object].methodMap.(anonymous function) (packages/meteorhacks:kadira/lib/hijack/wrap_session.js:160:1)
I20150608-11:11:05.295(-4)?     at maybeAuditArgumentChecks (packages/ddp/livedata_server.js:1617:1)
I20150608-11:11:05.295(-4)?     at packages/ddp/livedata_server.js:648:1

Here's my Meteor method:

var Reduced = new Mongo.Collection("donation_totals_by_donor");

    var map = function() {
      if(!this.donor) {
        return;
      }

      emit(this.donor, this.amount);
    }

    var reduce = function(donorId, totalAmount) {
      return Array.sum(totalAmount);
    }

    var result = Donations.mapReduce(
                  map,
                  reduce,
                  {
                    query: { createdAt: { $gte: new Date('Jan 1, ' + year), $lt: new Date('Jan 1, ' + (year + 1)) } },
                    out: "donation_totals_by_donor",
                    verbose: true
                  }
                 );

    return Reduced.find({}).fetch();

Answer 1

This error is the result of defining your collection multiple times. You need to move the new Mongo.Collection code outside of the method.

Typically you'd define your collections in a central location, e.g. lib/collections/mycollection.js. However, because this code is only running on the server you could just keep it at the top of this file or put it somewhere like server/collections/reduced.js.