如何在MongoDB PHP codeigniter中查询group by和distinct限制？

Question

Is such a operation possible?

sample record:

{ 
 _id: ObjectId("51d6be147483c58419000002"), 
 user: "ashok", 
 action: "login",
 time: 1373027860,
 details: { 
               user_entries:   "blah..blah", 
               url: "web.domain.com" 
                 }
 }

Suppose, i want to group by url visited, for each user, group by url where user = "ashok", limit 10.

I am using AlexBilbie library for MongoDB-Codeigniter (it doesnt have aggregation). so using plain php.
Still even if I could aggregate, how to distinct or limit it?
Any suggestion is welcome.

Answer 1

First of all using group_by and distinct together doesn't make any sense. Either you are using group_by or distinct.

If you want to do some kind of pagination for a grouped query you have to use map and reduce or the aggregation pipeline. In your case the aggregation would look like that.

db.users.aggregate(
  { '$match' => { 'user' => 'ashok' } },
  { '$group' => { '_id' => '$details.url' } },
  { '$skip'  => 0 },
  { '$limit' => 10 }
)

I am using this aggregation feature to display references at VersionEye . The aggregation feature allows to do grouping and paging on db level, that's why it's much faster then other ORM or pagination solutions.

Answer 2

在以下格式中，您可以给出限制：

$this->mongo_db->order_by(array('Student_Name'=>'asc'))->limit(20)->get('mycollection_name');