Sokil\Mongo\Operator::push PHP Method

    public function push($fieldName, $value)
    {
        // prepasre to store
        $value = Structure::prepareToStore($value);
        // no $push operator found
        if (!isset($this->operators['$push'])) {
            $this->operators['$push'] = array();
        }
        // no field name found
        if (!isset($this->operators['$push'][$fieldName])) {
            $this->operators['$push'][$fieldName] = $value;
        } else {
            if (!is_array($this->operators['$push'][$fieldName]) || !isset($this->operators['$push'][$fieldName]['$each'])) {
                $oldValue = $this->operators['$push'][$fieldName];
                $this->operators['$push'][$fieldName] = array('$each' => array($oldValue, $value));
            } else {
                $this->operators['$push'][$fieldName]['$each'][] = $value;
            }
        }
        return $this;
    }