Laravel is one of the most widely-used MVC frameworks for PHP, similar in architecture to Django and Rails from the Python and Ruby worlds respectively. We will follow through configuring our models using Laravel, Doctrine, and MongoDB. This section assumes that Doctrine is installed and working with Laravel 5.x.

Doctrine entities are Plain Old PHP Objects (POPO) that, unlike Eloquent, Laravel's default ORM doesn't need to inherit from the Model class. Doctrine uses the Data Mapper Pattern, whereas Eloquent uses Active Record. Skipping the get() and set() methods, a simple class would be shown in the following way:

use DoctrineORMMapping AS ORM;
use DoctrineCommonCollectionsArrayCollection;
/**
* @ORMEntity
* @ORMTable(name="scientist")
*/
class Scientist
{
   /**
    * @ORMId
    * @ORMGeneratedValue
    * @ORMColumn(type="integer")
    */
   protected $id;
   /**
    * @ORMColumn(type="string")
    */
   protected $firstname;
   /**
    * @ORMColumn(type="string")
    */
   protected $lastname;
   /**
   * @ORMOneToMany(targetEntity="Theory", mappedBy="scientist", cascade={"persist"})
   * @var ArrayCollection|Theory[]
   */
   protected $theories;
   /**
   * @param $firstname
   * @param $lastname
   */
   public function __construct($firstname, $lastname)
   {
       $this->firstname = $firstname;
       $this->lastname  = $lastname;
       $this->theories = new ArrayCollection;
   }
...
   public function addTheory(Theory $theory)
   {
       if(!$this->theories->contains($theory)) {
           $theory->setScientist($this);
           $this->theories->add($theory);
       }
   }

This POPO-based model uses annotations to define field types that need to be persisted in MongoDB. For example, @ORMColumn(type="string") defines a field in MongoDB with the string types firstname and lastname as the attribute names, in the respective lines.

There is a whole set of annotations available here: https://doctrine2.readthedocs.io/en/latest/reference/annotations-reference.html.

If we want to separate the POPO structure from annotations, we can also define them using YAML or XML instead of inlining them with annotations in our POPO model classes.