Doctrine\MongoDB\Query\Expr::push PHP Method

    public function push($valueOrExpression)
    {
        if ($valueOrExpression instanceof Expr) {
            $valueOrExpression = array_merge(['$each' => []], $valueOrExpression->getQuery());
        }
        $this->requiresCurrentField();
        $this->newObj['$push'][$this->currentField] = $valueOrExpression;
        return $this;
    }

 /**
  * Append one or more values to the current array field.
  *
  * If the field does not exist, it will be set to an array containing the
  * value(s) in the argument. If the field is not an array, the query
  * will yield an error.
  *
  * Multiple values may be specified by providing an Expr object and using
  * {@link Expr::each()}. {@link Expr::slice()} and {@link Expr::sort()} may
  * also be used to limit and order array elements, respectively.
  *
  * @see Expr::push()
  * @see http://docs.mongodb.org/manual/reference/operator/push/
  * @see http://docs.mongodb.org/manual/reference/operator/each/
  * @see http://docs.mongodb.org/manual/reference/operator/slice/
  * @see http://docs.mongodb.org/manual/reference/operator/sort/
  * @param mixed|Expr $valueOrExpression
  * @return self
  */
 public function push($valueOrExpression)
 {
     $this->expr->push($valueOrExpression);
     return $this;
 }