Entity/OrderElement.php
public function setProduct(ProductInterface $product)
    {
        $this->product = $product;

        $price = $product->IsInPromotion() === true ? $product->getPromotionPrice() : $product->getPrice();

        $this->setUnitPrice($price);
        $this->calculateTotalPrice();
        return $this;
    }
public function setProduct(ProductInterface $product)
    {
        $this->product = $product;

        $price = $product->IsInPromotion() === true ? $product->getPromotionPrice() : $product->getPrice();

        $this->setUnitPrice($price);
        $this->calculateTotalPrice();
        return $this;
    }
Set product

@param ProductInterface $product
@return OrderElement