如何使用usort对MongoDB查询结果进行排序

Question

Trying to sort array present in object but getting error usort() expects parameter 1 to be array I have not found any useful solution for this error on anywhere, How can I sort my array[detail] by total array elements count.

Here is my code -

$query = new MongoDB\Driver\Query($filter, $options);
$cursor = $manager->executeQuery("DB.col", $query);
foreach($cursor as $row) {
  foreach($row->detail as $item) {
    function cmp($a, $b) {
      return $a['detail'] > $b['detail'];
    }
    usort($row, "cmp");
  }
} 

Schema of my array:

array(
    [0]=>stdclass object( 
        [_id] => MongoDB\BSON\ObjectId Object (
                    [oid] => 5f55f95815a8508e2deac8dd
                )
        [Date] => 9/12/2020
        [title] => ram
        [roll.n] => 5
        [detail] => Array(
            [0] => stdclass object( 
                [title] => John
                [id] =>55
                [class] => six)
            [1] => stdclass object( 
                [title] => Doe
                [id] =>550
                [class] => six)
            [2] => stdclass object( 
                [title] => Jean
                [id] =>9
                [class] => one)
            [3] => stdclass object( 
                [title] => AI
                [id] =>90
                [class] => one)
            )
    )

    [1]=>stdclass object( 
        [_id] => MongoDB\BSON\ObjectId Object (
                [oid] => 5f
        )
        [title] => sunny
        [roll.n] => 50
        [detail] => Array(
            [0] => stdclass object ( 
                [title] => lilly
                [id] =>551
                [class] => six)
            [1] => stdclass object( 
                [title] => Doel
                [id] =>550
                [class] => six)
            [2] => stdclass object( 
                [title] => rehaman
                [id] =>9
                [class] => one
        )
    )
)

Answer 1

The executeQuery method returns a MongoDB\\Driver\\Cursor . It implements the Traversable interface so you are allowed to do foreach on it. This might have confused you to think it is an array. It's actually not.

To do usort on the result, you need to first turn the cursor into an array. Then, if I understand correctly, you are to sort the rows by the size of their 'detail' array like this:

$query = new MongoDB\Driver\Query($filter, $options);
$cursor = $manager->executeQuery("DB.col", $query);
$rows = $cursor->toArray();

usort($rows, function ($a, $b) {
  return sizeof($a->detail) <=> sizeof($b->detail);
});

return $rows;

Note: if the order is reversed, simply swap the $a->detail and $b->detail in the comparison function of usort() call.

If you're not using PHP 7, you might not have the spaceship operator <=> to use with. Simply use this comparison function instead:

usort($rows, function ($a, $b) {
  if (sizeof($a->detail) == sizeof($b->detail)) {
    return 0;
  }
  return (sizeof($a->detail) > sizeof($b->detail)) ? 1 : -1;
});

PS You should really upgrade to PHP 7. PHP 5.6 has been dropped from support for years. It's not as performant and less secure.