Sokil\Mongo\Document::getRelationDefinition PHP Method

    public function getRelationDefinition()
    {
        $relations = $this->getOption('relations');
        if (!is_array($relations)) {
            return $this->relations();
        }
        return $relations + $this->relations();
    }

 public function __construct(Document $document = null)
 {
     $this->document = $document;
     $this->relations = $document->getRelationDefinition();
 }