如何从mongoDB集合中的特定行（例如，第6行）获取数据？

Question

If my data in collection mongo is something like this

{ "_id" : ObjectId("4fff9946af8c6149aed251ab"), "subject_slug" : "math", "lesson_slug" : "mat01" }
{ "_id" : ObjectId("4fff9946af8c6149aed251ac"), "subject_slug" : "math", "lesson_slug" : "mat02" }
{ "_id" : ObjectId("4fff9946af8c6149aed251ad"), "subject_slug" : "math", "lesson_slug" : "mat03" }
{ "_id" : ObjectId("4fff9946af8c6149aed251ae"), "subject_slug" : "eng", "lesson_slug" : "eng01" }
{ "_id" : ObjectId("4fff9946af8c6149aed251af"), "subject_slug" : "eng", "lesson_slug" : "eng02" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b0"), "subject_slug" : "eng", "lesson_slug" : "eng03" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b1"), "subject_slug" : "phy", "lesson_slug" : "phy01" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b2"), "subject_slug" : "phy", "lesson_slug" : "phy02" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b3"), "subject_slug" : "phy", "lesson_slug" : "phy03" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b4"), "subject_slug" : "chem", "lesson_slug" : "che01" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b5"), "subject_slug" : "chem", "lesson_slug" : "che02" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b6"), "subject_slug" : "chem", "lesson_slug" : "che03" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b7"), "subject_slug" : "chem", "lesson_slug" : "che04" }

and If I want data in row 6 without loop data. Is there short code in php to get data in that row ???

Answer 1

In order to find the sixth record, you need to make use of some MongoCursor methods:

• sort() so there is a specific order (eg. by _id)
• skip() to skip a number of records (skip 5 to find the 6th)
• limit() to limit to one result

Code example:

<?php
    $mongo = new Mongo();
    $collection = $mongo->mydb->subject;

    $query = array();
    $sort  = array('_id' => 1);

    // Find the 6th record
    $doc = $collection->find($query)->sort($sort)->skip(5)->limit(1)->getNext();

    print_r($doc);
?>

Sample output:

Array
(
    [_id] => MongoId Object
        (
            [$id] => 4fff9946af8c6149aed251b0
        )

    [subject_slug] => eng
    [lesson_slug] => eng03
)

Note that the performance of skip() may be an issue if you need to skip over a large number of documents. A more performant option, if possible, would be to use range queries with a limit.