点餐系统学习日志-订单新建

```java      
@Override
@Transactional
public OrderDTO create(OrderDTO orderDTO) {
    String orderId = KeyUtil.genUniqueKey();
    BigDecimal  Count=new BigDecimal(BigInteger.ZERO);
    List<CartDTO> cartDTOList = new ArrayList<>();

    //1.查询商品
    for (OrderDetail detail:orderDTO.getOrderDetailList()){
        ProductInfo productInfo = productInfoService.findOne(detail.getProductId());
        if(productInfo==null){
            throw  new SellException(ResultEnum.PRODUCT_NOT_EXIST);
        }
        //2.计算总价
        Count= productInfo.getProductPrice().multiply
                (new BigDecimal(detail.getProductQuantity())).add(Count);
        //订单详情入库
        detail.setOrderId(orderId);
        detail.setDetailId(KeyUtil.genUniqueKey());
        detail.setProductName(productInfo.getProductName());
        detail.setProductPrice(productInfo.getProductPrice());
        detail.setProductIcon(productInfo.getProductIcon());
        orderDetailRepository.save(detail);
        CartDTO cartDTO = new CartDTO(detail.getProductId(), detail.getProductQuantity());
        cartDTOList.add(cartDTO);
    }
    //3.写入订单数据库 OrderMaster  OrderDetail
    OrderMaster  orderMaster= new OrderMaster();
    orderDTO.setOrderId(orderId);
    BeanUtils.copyProperties(orderDTO,orderMaster);
    orderMaster.setOrderAmount(Count);
    orderMaster.setOrderStatus(OrderStatusEnum.NEW.getCode());
    orderMaster.setPayStatus(PayStatusEnum.WAIT.getCode());
    orderMaster.setBuyerOpenid("oTgZpwTx-RzW8wIFHVkux4Uc1ROg");
    orderMasterRepository.save(orderMaster);
    //4.扣库存
    //Java8特性写法
    //        List<CartDTO> cartDTOList = orderDTO.getOrderDetailList().stream().map(e ->
    //                new CartDTO(e.getProductId(), e.getProductQuantity())
    //        ).collect(Collectors.toList());

    productInfoService.decreaseStock(cartDTOList);
    return orderDTO;
}

1.查询商品
遍历前端传来的商品集合id（里面只有商品id和商品数量）     
根据前端传来的商品id 和商品数量    
查询出商品 判断商品是否为null   

2.计算商品总价    
遍历时候计算商品总价    

3.订单详情入库      

4.订单入库    

5.减少库存