MongoDb aggregation or mapreduce for invoicing statistics? - mongodb

Question

I'm new to MongoDb and have a job for (I suppose) MapReduce or Aggregation.
I have an "invoices" collection with documents in this format:
{
date: 'some unix timestamp',
total: 12345,
paid: true
}
I need to display a table with months (jan-dec) as columns, a row for each year and the sum of total in the month (divided in paid and unpaid) in the cell. Like this:
| Jan | Feb | ...
2013 | 1,222 / 200 | 175 / 2,122 | ...
...
Can you help me get the mongo command right?
Maybe I'm better off writing some JS code to execute in mongo?

Answer 1

I've now found a solution using MapReduce. Here it is in use from PHP:
$map = new MongoCode('
function() {
var d = new Date(this.date*1000);
emit({y: d.getFullYear(), m: d.getMonth()}, {
total: this.total,
notPaid: this.paid ? 0 : this.total,
count: 1
});
};
');
$reduce = new MongoCode('
function(month, values) {
result = { total: 0, notPaid: 0, count: 0 };
for (var i = 0; i < values.length; i++) {
result.total += values[i].total;
result.notPaid += values[i].notPaid;
result.count += values[i].count;
}
return result;
};
');
$result = $db->command(array(
'mapreduce' => 'invoices',
'map' => $map,
'reduce' => $reduce,
'out' => 'temp'
));
echo $result['timeMillis'];
Now the results are in the "temp" collection, one document per month. Could it be optimized or enhanced?

Answer 2

You can do this with aggregation framework like this:
db.invoices.aggregate( [
{
"$project" : {
"yr" : {
"$year" : "$date"
},
"mo" : {
"$month" : "$date"
},
"total" : 1,
"unpaid" : {
"$cond" : [
"$paid",
0,
"$total"
]
}
}
},
{
"$group" : {
"_id" : {
"y" : "$yr",
"m" : "$mo"
},
"total" : {
"$sum" : "$total"
},
"unpaid" : {
"$sum" : "$unpaid"
}
}
}
] )
You can use another $project at the end to pretty-up the output, and a $sort to order it, but that's the basic functioning core of it.