我正在使用MongoDB 4.2开发PHP7。

我正在尝试使用聚合联接表。

我能够在mongo控制台上做

db.orders.aggregate([
    {
       $lookup: {
          from: "items",localField: "item",// field in the orders collection
          foreignField: "item",// field in the items collection
          as: "fromItems"
       }
    },{
       $replaceRoot: { newRoot: { $mergeObjects: [ { $arrayElemAt: [ "$fromItems",0 ] },"$$ROOT" ] } }
    },{ $project: { fromItems: 0 } }
])

并得到如下结果：

{ "_id" : 1,"item" : "almonds","description" : "almond clusters","instock" : 120,"price" : 12,"quantity" : 2 }
{ "_id" : 2,"item" : "pecans","description" : "candied pecans","instock" : 60,"price" : 20,"quantity" : 1 }

我想在PHP中做同样的事情，但没有得到结果：

我的PHP代码是：

<?php
public function demo_join() {

        global $mng; // $mng = new MongoDB\Driver\Manager("mongodb://localhost:27017");
        global $dbname;


        $command = new MongoDB\Driver\Command([
            'aggregate' => 'orders','pipeline' => [
                ['$lookup' => ["from" => "items","localField" => "items","foreignField" => "items","as" => "fromItems"]],],]);
        //$cursor = $mng->executeCommand($dbname,$command);

        try {
            $cursor = $manager->executeCommand($dbname,$command);
        } catch(MongoDB\Driver\Exception $e) {
            echo $e->getMessage(),"\n";
            exit;
        }
    return $cursor;

}

?>

并收到此错误：

 Uncaught Error: Call to a member function executeCommand() on null in $cursor = $manager->executeCommand($dbname,$command);

还有一段时间

 Uncaught MongoDB\Driver\Exception\CommandException: The 'cursor' option is required,except for aggregate with the explain argument in