Rails Best Practices

Hi Guy's,

I am new to map / reduce and trying to figure out a way to collect the following data using map / reduce instead doing it my (slow) application logic:

I have a collection 'challenge' with a 1:n relation to a collection 'tasks'. Now I'd like to receive an array of results that gives top five heightest scored challenge.

For map I tried something like:

map = function () { emit(this.user_id, { count:1 }); }

and reduce:

reduce = function (key, score) { var sum = 0; score.forEach(function(doc){ sum += 1; }); return { count:sum }; }

I fired this against my tasks collection:

var mr = db.tasks.mapReduce(map, reduce, { out: "results" }); But I get crucial results when querying:

db[mr.result].find(); I am using Mongoid on Rails and am completely lost with it. Can someone point me into the right direction?

my data something like this

/ 13 / { "_id" : ObjectId("4ef1a6a454b53001a4000067"), "user_id" : "100002573213371", "title" : "social who wins", "description" : "social who wins", "updated_at" : new Date("Wed, 21 Dec 2011 14:58:04 GMT +05:30"), "created_at" : new Date("Wed, 21 Dec 2011 14:58:04 GMT +05:30"), "tasks" : [{

  "is_complete" : 0,
  "score_by" : "Check box:1 for checking off the task",
  "score" : "5",
  "name" : "task no 1",
  "_id" : ObjectId("4ef1a6a454b53001a4000068")
}, {
  "is_complete" : 0,
  "score_by" : "Self-report number",
  "score" : "6",
  "name" : "task no 2",
  "_id" : ObjectId("4ef1a6a454b53001a4000069")
}],

}

/ 14 / { "_id" : ObjectId("4ef1a6a454b53001a400006d"), "canCompleteBeforeTasks" : true, "challenge_id" : ObjectId("4ef1a6a454b53001a4000067"), "created_at" : new Date("Wed, 21 Dec 2011 14:58:04 GMT +05:30"), "description" : "social who wins", "tasks" : [{

  "is_complete" : 0,
  "score_by" : "Check box:1 for checking off the task",
  "score" : "5",
  "name" : "task no 1",
  "_id" : ObjectId("4ef1a6a454b53001a400006e")
}, {
  "is_complete" : 0,
  "score_by" : "Self-report number",
  "score" : "7",
  "name" : "task no 2",
  "_id" : ObjectId("4ef1a6a454b53001a400006f")
}],

"title" : "social who wins", "updated_at" : new Date("Wed, 21 Dec 2011 14:58:04 GMT +05:30"), "user_id" : "100003135115833" }

/ 15 / { "_id" : ObjectId("4ef1a6a454b53001a4000073"), "challenge_id" : ObjectId("4ef1a6a454b53001a4000067"), "created_at" : new Date("Wed, 21 Dec 2011 14:58:04 GMT +05:30"), "description" : "social who wins", "tasks" : [{

  "is_complete" : 0,
  "score_by" : "Check box:1 for checking off the task",
  "score" : "5",
  "name" : "task no 1",
  "_id" : ObjectId("4ef1a6a454b53001a4000074")
}, {
  "is_complete" : 0,
  "score_by" : "Self-report number",
  "score" : "8",
  "name" : "task no 2",
  "_id" : ObjectId("4ef1a6a454b53001a4000075")
}],

"title" : "social who wins", "updated_at" : new Date("Wed, 21 Dec 2011 14:58:04 GMT +05:30"), "user_id" : "100003174704960" }

Thx in advance.

++++++++++++++++ Pravin Mishra