Mybatis-plus-Join--分页查询

数据表四张：

user： id,username,create_time,update_time

product： id,name,price,number(库存),create_time,update_times

order： id,quantity,order_time(下单时间),update_time

order_detail:id,product_id,order_id,quantity,price,create_time,update_time

1、UserService接口：

List<UserDTO> selectAll(int pageNum, int pageSize);

2、封装的UserDTO类（想在前端展示什么内容，就封装什么属性）

package com.xxxx.DTO;import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.xxxx.entity.OrderDetail;
import io.swagger.annotations.ApiModelProperty;
import lombok.Data;import java.time.LocalDateTime;
import java.util.List;
@Data
public class OrderDTO {@ApiModelProperty(value = "订单ID")@TableId(value = "id", type = IdType.AUTO)private Integer id;@ApiModelProperty(value = "订单数量")private Integer quantity;@ApiModelProperty(value = "下单时间")@TableField(fill = FieldFill.INSERT ,value = "order_time")private LocalDateTime orderTime;@ApiModelProperty(value = "修改时间")@TableField(fill = FieldFill.INSERT_UPDATE ,value = "update_time")private LocalDateTime updateTime;@ApiModelProperty(value = "用户id")@TableField(value = "user_id")private Integer userId;/*** 订单和订单详情是一对多*/private List<OrderDetail> orderDetailList;

3、重点：UserServiceImpl 中的实现逻辑

注入：

@Autowired
private UserMapper userMapper;

 @Overridepublic List<UserDTO> selectAll(int pageNum, int pageSize) {//用户： 订单   1： n//订单 ： 订单详情 1： n//订单详情 ： 商品 1： 1MPJLambdaWrapper<User> wrapper=new MPJLambdaWrapper<>(User.class).selectAll(User.class)//用户： 订单   1： n.selectCollection(OrderDetail.class,UserDTO::getOrderDetailList).leftJoin(Order.class,Order::getUserId,User::getId).leftJoin(OrderDetail.class,OrderDetail::getOrderId,Order::getId);return userMapper.selectJoinList(UserDTO.class,wrapper);}

4、UserControler

    @Resourceprivate UserService userService;/*** 分页查询所有用户及详情*/@PostMapping("selectAllPage")public List<UserDTO> selectByPage(int pageNum, int pageSize){return userService.selectAll(pageNum,pageSize);}

5、再PostMan中测试

访问路径：http://localhost:9999/springboot_mp/selectAllPage?pageNum=1&pageSize=3

[
{
"id": 1,
"username": "张三",
"orderDetailList": [
{
"id": 1,
"productId": 1,
"orderId": 1,
"quantity": 3,
"price": 3000.00,
"createTime": "2024-12-17T15:24:20",
"updateTime": "2024-12-17T15:24:20"
},
{
"id": 2,
"productId": 3,
"orderId": 1,
"quantity": 1,
"price": 2300.00,
"createTime": "2024-12-17T15:24:20",
"updateTime": "2024-12-17T15:24:20"
},
{
"id": 5,
"productId": 1,
"orderId": 3,
"quantity": 9,
"price": 3000.00,
"createTime": "2024-12-17T15:25:55",
"updateTime": "2024-12-17T15:25:55"
},
{
"id": 6,
"productId": 3,
"orderId": 3,
"quantity": 10,
"price": 2300.00,
"createTime": "2024-12-17T15:25:55",
"updateTime": "2024-12-17T15:25:55"
}
]
}
]