How to "Group By" with MongoDB

Question

I would like to know if there is anyway I can "group by" my results with MongoDB/Php.

This is the code I'm using to display my rows:

$count = $col->find(array('order_id' => array('$gt' => '0')))->count();

I need to group them by order_id.

Apparently, we cannot do a count() on a group() as find()

WORKS: $countfind = $col->find()->count();

DOESN'T WORK: $countgroup = $col->group($keys)->count();

I need to count this groupby please.

Thanks for your help.

Answer 1

New answer using Mongo aggregation framework

After this question was asked and answered, 10gen released Mongodb version 2.2 with an aggregation framework. So the new best way to do Group By is with the $group operator. In PHP use MongoCollection::aggregate.

FYI, 10gen also has a handy SQL to Mongo Aggregation conversion chart worth bookmarking. It has examples of all the common SQL queries that use SQL aggregation and how to translate them to Mongo.

Answer 2

Sometimes you may want to get an array of distinct values in a collection. You can accomplish this using the distinct() method:

$ages = $dm->createQueryBuilder('User')
->distinct('age')
->getQuery()
->execute();

http://docs.doctrine-project.org/projects/doctrine-mongodb-odm/en/latest/reference/query-builder-api.html

Answer 3

There's some detailed documentation on the Group command on their website.

There are some examples of Group using the PHP libarary here.

If your data set is really big, you may need to look at running map-reduces to "pre-group" this data.