Get error 'MongoResultException' when use aggregate in mongoDB - php

Question

When i use aggregatein PHP, i get error:
MongoResultException: localhost:27017: The 'cursor' option is
required, except for aggregate with the explain argument
I use mongoDB 3.6 and PHP 5.6
Please see the photo
My Code:
$dbconn = new MongoClient();
$c = $dbconn->selectDB("test")->selectCollection("users");
$ops = array(
array(
'$lookup' => array(
'from' => 'news',
'localField' => '_id',
'foreignField' => 'user_id',
'as' => 'user_docs'
)
)
);
$results = $c->aggregate($ops);
var_dump($results);

Answer 1

For other people who may run into the same problem, here is the solution.
The aggregator command was modified in version 3.6, as indicated in the documentation:
Changed in version 3.4: MongoDB 3.6 removes the use of aggregate command without the cursor option unless the command includes the explain option. Unless you include the explain option, you must specify the cursor option.
In Mongo, you could just add the cursor option without specifying any parameter, as specified in the documentation:
cursor: {}
In PHP, you would need to specify the option like this, new stdClass()corresponding to an empty object '{}' in Mongo :
$results = $c->aggregate($ops, ['cursor' => new \stdClass()]);
Here's how to do it for your example :
$dbconn = new MongoClient();
$c = $dbconn->selectDB("test")->selectCollection("users");
$ops = array(
array(
'$lookup' => array(
'from' => 'news',
'localField' => '_id',
'foreignField' => 'user_id',
'as' => 'user_docs'
)
)
);
$results = $c->aggregate($ops, ['cursor' => new \stdClass()]);
var_dump($results);
If you want to take advantage of calling 'cursor' to add parameters, such as batchSize, you can do it like this :
$results = $c->aggregate($ops, ['cursor' => ['batchSize' => 200]]);
All the parameters are listed in the documentation page linked above.