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mongo sort after limit after sort - Not working

Tags:

php

mongodb

I have a collection, from which i get particular type of users using $query
Then I need sort them according to user_id ascending and limit them to 2000

From these I need the max user_id, so I sort them in descending order and limit to 1.

But this second sort forgets the limit of 2000 and sorts over over the entire cursor from find().

Any work-around?

$cursor = $collection   ->find($query)                // too many entries
            ->sort(array('user_id'=>1))   // go ascending
            ->limit(2000)                // got our limited qouta
            ->sort(array('user_id'=>-1)) // go descending to get max
            ->limit(1);          // the one with max(user_id)
like image 408
davneetnarang Avatar asked Jan 20 '13 10:01

davneetnarang


1 Answers

Your cannot do a sort and then a limit and then a sort. The Cursor object is exactly that and it will not run the query until you iterate to the first result via getNext() which is either run manually or within a foreach loop not only that but sort is just a property of the object as such making two sorts just overwrites the property.

The best way to achieve what your looking for is:

$doc = $collection->find($query)->sort(array('user_id' => 1))
       ->skip(1999)->limit(1)->getNext();

That will always pick the highest user_id (which occurs at the end in this sort) of the group, which will give off the same results as doing two sorts.

like image 127
Sammaye Avatar answered Nov 03 '22 00:11

Sammaye