Cloud Datastore Client - Class AggregationQuery (1.33.1)

 use Google\Cloud\Datastore\DatastoreClient;
use Google\Cloud\Datastore\Query\Aggregation;

$datastore = new DatastoreClient();

$query = $datastore->query();
$query->kind('Companies');
$query->filter('companyName', '=', 'Google');
$aggregationQuery = $query->aggregation(Aggregation::count()->alias('total'));

$res = $datastore->runAggregationQuery($aggregationQuery);
echo $res->get('total'); 

 use Google\Cloud\Datastore\DatastoreClient;
use Google\Cloud\Datastore\Query\Aggregation;

$datastore = new DatastoreClient();

$query = $datastore->query();
$query->kind('Companies');
$query->filter('companyName', '=', 'Google');
$query->limit(100);
$aggregationQuery = $datastore->aggregationQuery();
$aggregationQuery->over($query)->addAggregation(Aggregation::count()->alias('total_upto_100'));

$res = $datastore->runAggregationQuery($aggregationQuery);
echo $res->get('total_upto_100'); 

 $query = $datastore->AggregationQuery();
$query->kind('Companies');
$query->filter('companyName', '=', 'Google');
$query->addAggregation(Aggregation::count()->alias('total'));
echo json_encode($query->queryObject()); 

 $query = $datastore->query();
$query->kind('Companies');
$query->filter('companyName', '=', 'Google');

$pipeline = $datastore->AggregationQuery()
    ->over($query)
    ->addAggregation(Aggregation::count()->alias('total'));