Unable to $push documents to array

[rms2219]

I have a collection called "Contracts" with a field called "projects", which is an array of documents. Each document in the array would have an _id (a MongoID) and a 'projectName' (a string). I'm attempting to use the "push" function to append this array, but I cannot figure out how to add documents.

$projectId = new MongoId();
$test = DB::collection('Contracts')
            ->where('_id', $contractId)
            ->push('projects', array( '{ _id : '.$projectId.', projectName : <Project> }'));

The above code doesn't work, and I'm not sure how to do exactly what I'm trying to do. In addition, where I'm concatenating the $projectId, I really want that to be a new ObjectId.

How could I do this?
Thanks!

[jenssegers]

I added an example to the readme for your question:

DB::collection('users')->where('name', 'John')->push('messages', array('from' => 'Jane Doe', 'message' => 'Hi John'));