MapReduce with MongoDB & Node.js
Here’s some generic code for doing map-reduce queries in node using the node-mongodb-native driver.
Suggestions welcome!
Good resoureces:
http://www.mongodb.org/display/DOCS/MapReduce
http://kylebanker.com/blog/2009/12/mongodb-map-reduce-basics/
https://github.com/christkv/node-mongodb-native
var mongodb = require('mongodb'),
server = new mongodb.Server("localhost", 27017, {}),
sys = require('util'),
db = new mongodb.Db('MY_DATABASE_NAME', server, {}),
db.open(function (error, client) {
if (error) throw error;
var mapFn = function(){
var n = this.someArray.length
emit(
this._id,
{
someArrayVals : (n > 0 ? n : 0)
}
);
}
var reduceFn = function(key, values) {
var sum = 0;
var rows = 0;
values.forEach(function(doc) {
sum += doc.someArrayVals;
rows += 1;
});
return {someArrayVals: sum, rows : rows };
};
var MR = {
mapreduce: "my_collection",
out: { inline : 1 },
map: mapFn.toString(),
reduce: reduceFn.toString()
}
db.executeDbCommand(MR, function(err, dbres) {
var results = dbres.documents[0].results
console.log("executing map reduce, results:")
console.log(JSON.stringify(results))
process.exit(1)
})
})1 month ago - 
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