MongoDB course m0101 homework 3-2 for node.js

removing.js

var mongodb = require('mongodb');
var _ = require('underscore');

var db = mongodb.Db('school', new mongodb.Server('localhost', 27017), {safe: true});

db.open(function(err, client) {
	if(err) {
		console.log('Error opening connection' + err);
	}
	console.log('db opened');
	
	var collection = new mongodb.Collection(client, 'students');
	
	// find all students that have at least one homework score
	// ( note: all stundents have, so this query is not really needed )
	var query = {"scores.type":"homework"};
	// no need for sorting
    var options = {};
	
    collection.find(query,options).toArray(function(err, docs) {
		if (err) {
			console.log(err);
		}
		// loop all docs (students)
		_.each(docs, function(doc) {
            // loop the students' scores and find the lowest homework
		    var lowScore = 9999.9;
		    for ( var i=0; i<doc.scores.length; i++ ) {
     		    if ( doc._id == 100 && doc.scores[i].type == "homework" ) { console.log("id 100 hw "+doc.scores[i].score); }
		        if ( doc.scores[i].type == "homework"
		           && doc.scores[i].score < lowScore ) {
		                lowScore = doc.scores[i].score;
		        }
		    }
		    if ( doc._id == 100 ) { console.log("lowScore "+lowScore); }
		    // update student pulling the homework-score with the found lowest score
		    collection.update({ "_id":doc._id }, 
		                      { $pull : { "scores" : {
		                          $and: [ {"type":"homework"}, { "score":lowScore} ]
		                      } } },
		                      { "safe":true },
		                      function( err, result ) {
		                          if (err) {
		                              console.log(err);
		                          }
		                          // if (doc._id == 100) { console.log("id 100 updated "+result); }
		                          // console.log("callback "+result);
		                      } // update callback
		                      ); // update
		}); // each student
		console.log('done');
		client.close();
    }); // find()
}); // db.open()

using mapReduce.js

// for node.js
// homework 3-1 without removing the lowest scores
// see hw31.js for "normal" way

var mongodb = require('mongodb');
var _ = require('underscore');

var db = mongodb.Db('school', new mongodb.Server('localhost', 27017), {safe: true});

db.open(function(err, client) {
	if(err) {
		console.log('Error opening connection' + err);
	}
	console.log('db opened');
	var Students = new mongodb.Collection(client, 'students');
	console.log('Students collection');

    // set up the stuff for mapReduce:
    // ono query
	var qry = {};
	
	// per student map the score and the _id of the document
    var mapf = function() {
        var low = 0;
        // loop the scores and emit one record per score (all types !!)
        for ( var i=0; i<this.scores.length; i++ ) {
            low =  ( this.scores[i].type == "homework" ? this.scores[i].score : 9999.9 );
            emit( this._id,
                  {
                      student_id: this._id,
                      name: this.name,
                      count: 1,
                      sum: this.scores[i].score,
                      low: low,
                      average: 0
                  }
            ); // emit
        }; // loop scores
    }; // mapf
    
    // reduce this to one record per student
    // remembering the lowest homework score; count and sum all scores (for the average)
    var reducef = function(key, values) {
            var r = {
                      student_id: key,
                      name: null,
                      count: 0,
                      sum: 0,
                      low: 9999,
                      average: 0
                    }      
            // loop all values emitted by mapf 
            values.forEach(function(v) {
                r.student_id = v.student_id;
                r.name = v.name;
                r.count += v.count;
                r.sum += v.sum;
                r.low = ( v.low < r.low ? v.low : r.low );
            });
            return r;
    };
    
    // this will be called once per student:
    // compute average without lowest score
    var finalizef = function(key, value) {
        value.average = ( value.count == 1 ? 0.0 : 
            (value.sum - value.low) / (value.count - 1) );
        return value;
    };
    
    // call it
    Students.mapReduce(mapf, reducef,
        {
            query: qry,
            finalize: finalizef,
            out: { replace: "students_hw31_mr" }
        },
        function(err, rsltColl) { 
	        if (err) {
		        console.log(err);
	        }  
	        console.log('mapReduce callback...');
	        // compute the result for HW 3-1:
	        // -- find the student_id with the highest average
	        rsltColl.find({},{},{sort:[["value.average","desc"]],limit:1})
	                .toArray(function(err, docs) {
    	        if (err) {
		            console.log(err);
	            }
	            console.log('and the answer is: ' + docs[0].value.student_id); 
	            client.close();
            }); // find toArray result
        } // mapReduce callback
    ); // mapReduce()
}); // db.open()