如何使用 PHP 中的 MongoDB\\Driver 查询获取 find() 结果的长度？

Question

I have a MongoDB server with a collection counting hundreds of thousands of documents.

I need to get only the number of documents matching the query filter condition using MongoDB\\Driver in PHP.

In mongo-shell I would simply do the following:

db.samples.find({"location": {$geoWithin: {$geometry: ...reference_polygon... }}}).length

The below query in PHP would return a cursor with the full list of the documents (could be thousands of docs) which I don't need, I'm only looking for the number of the samples within a specified polygon:

$query = new MongoDB\Driver\Query( 
    ["location" => ['$geoWithin' => ['$geometry' => $reference_polygon]]],
    []
);
$cursor = $dbm->executeQuery("test.samples", $query);

Even reducing projection to return a single field as _id would significantly increase the calculation time.

Is there any way to get just a scalar number of documents and avoid loading cursor results and then counting it like count($cursor->toArray()) ?

MongoDB Server: 4.4.1 PHP version: 7.4 OS: Ubuntu 20.04 LTS

Answer 1

So, finally, I found a way to do it using MongoDB\\Driver\\Command .

The code is below, would someone have a better proposal, please feel free to comment.

$database_name = "test";
$collection_name = "samples";
$query = new MongoDB\Driver\Query( 
    ["location" => ['$geoWithin' => ['$geometry' => $reference_polygon]]],
    []
);
$dbc = new MongoDB\Driver\Command(
    ['count' => $collection_name, "query" => (object)$query]
);
$cursor = $dbm->executeCommand($database_name, $dbc);
$n = (isset($cursor->toArray()[0]->n)) ? $cursor->toArray()[0]->n : 0;