1)交易模型设计

   交易模型(用户下单的交易模型)OrderModel

   id(String 交易单号使用String)， userId，itemId，amount(数量)，orderAmount(总金额)，       itemPrice(购买时的价格)

   创建表order_info

     id,userId,item_id,item_price,amount,order_amount

2）使用mybatis-generator生成对应的文件

3）生成订单的流程

      1）校验商品是否存在，用户是否合法，购买数量是否正确

      2）落单减库存（需要在ItemServiceImpl里添加方法用户更新库存数量，这里需要添加sql语句更新库存）

      3) 生成订单（订单有一定的规则:这里是16位，由时间，自增序列，分库分表组成）

      4）订单入库

       5）添加销量（需要在itemServiceImpl里添加方法更新销量，并且需要新增sql语句）

 OrderModel

package com.miaoshaproject.service.model;import java.math.BigDecimal;public class OrderModel {    private String id;    private Integer userId;    private Integer itemId;    private Integer amount;    private BigDecimal orderAmount;    private BigDecimal itemPrice;    public String getId() {        return id;    }    public void setId(String id) {        this.id = id;    }    public Integer getUserId() {        return userId;    }    public void setUserId(Integer userId) {        this.userId = userId;    }    public Integer getItemId() {        return itemId;    }    public void setItemId(Integer itemId) {        this.itemId = itemId;    }    public Integer getAmount() {        return amount;    }    public void setAmount(Integer amount) {        this.amount = amount;    }    public BigDecimal getOrderAmount() {        return orderAmount;    }    public void setOrderAmount(BigDecimal orderAmount) {        this.orderAmount = orderAmount;    }    public BigDecimal getItemPrice() {        return itemPrice;    }    public void setItemPrice(BigDecimal itemPrice) {        this.itemPrice = itemPrice;    }}

OrderService

package com.miaoshaproject.service;import com.miaoshaproject.error.BusinessException;import com.miaoshaproject.service.model.OrderModel;public interface OrderService {    OrderModel createModel(Integer userId, Integer itemId, Integer amount) throws BusinessException;}

OrderServiceIpml

package com.miaoshaproject.service.impl;import com.miaoshaproject.dao.ItemDOMapper;import com.miaoshaproject.dao.OrderDOMapper;import com.miaoshaproject.dao.SequenceDOMapper;import com.miaoshaproject.dao.UserDOMapper;import com.miaoshaproject.dataobject.ItemDO;import com.miaoshaproject.dataobject.OrderDO;import com.miaoshaproject.dataobject.SequenceDO;import com.miaoshaproject.dataobject.UserDO;import com.miaoshaproject.error.BusinessException;import com.miaoshaproject.error.EmBusinessError;import com.miaoshaproject.service.OrderService;import com.miaoshaproject.service.model.ItemModel;import com.miaoshaproject.service.model.OrderModel;import com.miaoshaproject.service.model.UserModel;import org.springframework.beans.BeanUtils;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;import org.springframework.transaction.annotation.Propagation;import org.springframework.transaction.annotation.Transactional;import java.math.BigDecimal;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;import java.util.Date;@Servicepublic class OrderServiceImpl implements OrderService {    @Autowired    private ItemServiceImpl itemService;    @Autowired    private UserServiceImpl userService;    @Autowired    private ItemDOMapper itemDOMapper;    @Autowired    private UserDOMapper userDOMapper;    @Autowired    private OrderDOMapper orderDOMapper;    @Autowired    private SequenceDOMapper sequenceDOMapper;    @Override    @Transactional //保证订单是在同一事务当中？    public OrderModel createModel(Integer userId, Integer itemId, Integer amount) throws BusinessException {       //1校验下单状态，下单的商品是否存在，用户是否合法，购买数量是否正确       ItemModel itemModel = itemService.getItemById(itemId);       if(itemModel == null){           throw new BusinessException(EmBusinessError.PARAMTER_VALIDATION_ERROR,"商品信息不存在");       }       UserModel userModel =userService.getUserById(userId);       if(userModel == null){           throw new BusinessException(EmBusinessError.PARAMTER_VALIDATION_ERROR,"用户不存在");       }       if(amount<=0 || amount>99){           throw new BusinessException(EmBusinessError.PARAMTER_VALIDATION_ERROR,"商品数量不正确");       }       //2.落单减库存       boolean result =itemService.decreaseStock(itemId,amount);       if(!result){           throw new BusinessException(EmBusinessError.STOCK_NOT_ENOUGH);       }       //3.订单入库       OrderModel orderModel = new OrderModel();       orderModel.setUserId(userId);       orderModel.setItemId(itemId);       orderModel.setAmount(amount);       orderModel.setItemPrice(itemModel.getPrice());       orderModel.setOrderAmount(itemModel.getPrice().multiply(new BigDecimal(amount)));       //生成订单号       orderModel.setId(generatorOrderNo());       OrderDO orderDO=this.convertOrderDOFromOrderModel(orderModel);       orderDOMapper.insertSelective(orderDO);       //加上销售额        itemService.increaseSales(itemId,amount);        //返回前端        return orderModel;    }    public OrderDO convertOrderDOFromOrderModel(OrderModel orderModel){        OrderDO orderDO = new OrderDO();        if(orderModel == null){            return null;        }        BeanUtils.copyProperties(orderModel,orderDO);        orderDO.setItemPrice(orderModel.getItemPrice().doubleValue());        orderDO.setOrderAmount(orderModel.getOrderAmount().doubleValue());        return orderDO;    }    @Transactional(propagation = Propagation.REQUIRES_NEW)    public String generatorOrderNo(){        //订单号有16        StringBuilder stringBuilder = new StringBuilder();        // 前8位是时间年月日        LocalDateTime now = LocalDateTime.now();        String nowDate = now.format(DateTimeFormatter.ISO_DATE).replace("-","");        stringBuilder.append(nowDate);        //中间6位是自增序列,        // 创建sequence_info表有字段name current_value step        //每次加step，然后更新表，不够6位用0补上        int sequence = 0;        SequenceDO sequenceDO = sequenceDOMapper.getSequenceByName("order_info");        sequence = sequenceDO.getCurrentValue();        sequenceDO.setCurrentValue(sequenceDO.getCurrentValue()+sequenceDO.getStep());        sequenceDOMapper.updateByPrimaryKey(sequenceDO);        String sequenceStr = String.valueOf(sequence);        for(int i=0;i<6 - sequenceStr.length(); i++){            //这里需要考虑的一点是如果大于6的            // 时候怎么处理            stringBuilder.append(0);        }        stringBuilder.append(sequenceStr);        //最后两位是分库分表位,这里而写死        stringBuilder.append("00");       return stringBuilder.toString();    }}

OrderController

package com.miaoshaproject.controller;import com.miaoshaproject.error.BusinessException;import com.miaoshaproject.error.EmBusinessError;import com.miaoshaproject.response.CommonReturnType;import com.miaoshaproject.service.impl.OrderServiceImpl;import com.miaoshaproject.service.model.OrderModel;import com.miaoshaproject.service.model.UserModel;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Controller;import org.springframework.web.bind.annotation.*;import javax.servlet.http.HttpServletRequest;@RestController@RequestMapping("/order")@CrossOrigin(allowCredentials = "true",allowedHeaders = "*")public class OrderController extends BaseController{    @Autowired    private HttpServletRequest httpServletRequest;    @Autowired    private OrderServiceImpl orderService;    @RequestMapping(value="create",method = RequestMethod.POST,consumes = {CONTENT_TYPE_FORMED})    public CommonReturnType createOrder (@RequestParam(name="itemId")Integer itemId,                                         @RequestParam(name="amount")Integer amount    ) throws BusinessException {        Boolean isLogin = (Boolean)httpServletRequest.getSession().getAttribute("IS_LOGIN");        if(isLogin == null||!isLogin.booleanValue()){            throw new BusinessException(EmBusinessError.USER_NOT_LOGIN,"用户还未登入不能下单");        }        UserModel userModel=(UserModel) httpServletRequest.getSession().getAttribute("LOGIN_USER");        //进行下单操作        OrderModel orderModel=orderService.createModel(userModel.getId(),itemId,amount);        return CommonReturnType.create(null);    }}