SSM多表查询

因为在订单类（Order）中涉及产品类（Product）的产品名称（ProductName）和产品价格（ProductPrice），所以需要使用联合查询。

1.项目结构：

2.重新定义的实体类代码OrderProduct：

public class OrderProduct extends Orders {
//    此处继承Orders类并重新定义Product类
    private Product product;

    public Product getProduct() {
        return product;
    }

    public void setProduct(Product product) {
        this.product = product;
    }
    @Override
    public String toString() {
        return "OrderProduct{" +
                "product=" + product +
                '}';
    }
}

3.OrderService代码

List<OrderProduct> findAll(int page, int size);
//int page，int size为分页，如不用可以删除

4.OrderServiceImpl代码

@Service
public class OrdersServiceImpl implements OrdersService {
   @Autowired
   private OrdersMapper ordersMapper;
    @Override
    public List<OrderProduct> findAll(int page, int size) {
    //此处为开启分页插件，page size为分页参数，如不用可以删除
        PageHelper.startPage(page,size);
        return this.ordersMapper.findAll();
    }
}

5.OrderMapper代码

public interface OrdersMapper {
    int deleteByPrimaryKey(String id);

    int insert(Orders record);
    //查询所有
    List<OrderProduct> findAll();
    
    Orders selectByPrimaryKey(String id);
    
    int updateByPrimaryKey(Orders record);
}

6.OrderMapper.xml

<resultMap id="OrderProduct" type="com.hhxy.plx.domain.OrderProduct">
    <id column="id" property="id" jdbcType="VARCHAR" />
    <result column="ordernum" property="ordernum" jdbcType="VARCHAR" />
    <result column="ordertime" property="ordertime" jdbcType="TIMESTAMP" />
    <result column="peoplecount" property="peoplecount" jdbcType="INTEGER" />
    <result column="orderdesc" property="orderdesc" jdbcType="VARCHAR" />
    <result column="paytype" property="paytype" jdbcType="INTEGER" />
    <result column="orderstatus" property="orderstatus" jdbcType="INTEGER" />
    <result column="productid" property="productid" jdbcType="VARCHAR" />
    <result column="memberid" property="memberid" jdbcType="VARCHAR" />
    <association property="product" javaType="com.hhxy.plx.domain.Product">
      <id column="id" property="id" jdbcType="VARCHAR" />
      <result column="productName" property="productName" jdbcType="VARCHAR" />
      <result column="productPrice" property="productPrice" jdbcType="DECIMAL" />
    </association>
  </resultMap>

<select id="findAll" resultMap="OrderProduct" >
    select
          a.* ,
           b.productName,
           b.productPrice
# 这里为查询a的所有，b中的名字和价格
    from
         orders as a
#                  定义别名order为a
    left outer join
         product as b
#                  定义别名order为a
    on
         a.productid=b.id
#            a中的productid为b中的id

  </select>

7.OrderController代码

 @Autowired
   private OrdersService ordersService;
    @RequestMapping("/findAll.do")
    public ModelAndView findAll(@RequestParam(name = "page",required = true,defaultValue = "1")int page,
                                @RequestParam(name = "size",required = true,defaultValue = "4")int size, 
　　　　　　　　　　　　　　　　　　　 Model model)throws Exception{
        ModelAndView mv = new ModelAndView();
        List<OrderProduct> orderProductsList=ordersService.findAll(page, size);
       PageInfo pageinfo =new PageInfo(orderProductsList);
       model.addAttribute("pageinfo",pageinfo);
       model.addAttribute("orderProductsList",orderProductsList);
      mv.setViewName("orders-list");

        return mv;
    }

8.jsp页面

                               <tbody>
                                    <c:forEach items="${pageinfo.list}" var="orders">
                                        <tr>
                                            <td><input name="ids" type="checkbox"></td>
                                            <td>${orders.id }</td>
                                            <td>${orders.ordernum }</td>
                                            <td>${orders.product.productName }</td>
                                            <td>${orders.product.productPrice }</td>
                                            <td>${orders.ordertimestr }</td>
                                            <td class="text-center">${orders.orderstatusstr }</td>
                                            <td class="text-center">
                                                <button type="button" class="btn bg-olive btn-xs">订单</button>
                                                <button type="button" class="btn bg-olive btn-xs" onclick="location.href='${pageContext.request.contextPath}/orders/findById.do?id=${orders.id}'">详情</button>
                                                <button type="button" class="btn bg-olive btn-xs">编辑</button>
                                            </td>
                                        </tr>
                                    </c:forEach>
                                </tbody>

9.结束。