1天搞定SpringBoot+Vue全栈开发 (4)多表查询及分页查询-编程知识

1.多表查询

在多表查询中，mybatis和mybatis plus无区别

User:

package com.example.mpdemo.entity;import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;import java.util.List;@TableName("user")
public class User{@TableId(type= IdType.AUTO)private int id;private String username;private String password;private String birthday;//描述用户的所有订单@TableField(exist = false)private  List<Order> orders;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getBirthday() {return birthday;}public void setBirthday(String birthday) {this.birthday = birthday;}public List<Order> getOrders() {return orders;}public void setOrders(List<Order> orders) {this.orders = orders;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", password='" + password + '\'' +", birthday='" + birthday + '\'' +", orders=" + orders +'}';}
}

UserController:

package com.example.mpdemo.controller;import com.alibaba.druid.pool.ha.selector.StickyDataSourceHolder;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.example.mpdemo.entity.User;
import com.example.mpdemo.mapper.UserMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.List;@RestController
public class UsrController {@AutowiredUserMapper userMapper;@GetMapping("/user/findAll")public List<User> find(){return userMapper.selectAllUserAndOrders();}}

UserMapper:

package com.example.mpdemo.mapper;import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.mpdemo.entity.User;
import org.apache.ibatis.annotations.*;
import org.springframework.stereotype.Repository;import java.util.List;@Mapper
@Repository
public interface UserMapper extends BaseMapper<User> {//查询用户，根据用户id查询信息 select * from user where id=@Select("select * from user where id=#{id}")User selectById(int id);//查询用户及其所有订单@Select("select * from user")@Results({@Result(column = "id",property = "id"),@Result(column = "username",property = "username"),@Result(column = "password",property = "password"),@Result(column = "birthday",property = "birthday"),@Result(column = "id",property = "orders",javaType = List.class,//many：一个用户可以有多个订单many=@Many(select = "com.example.mpdemo.mapper.OrderMapper.selectByUid" ))})List<User> selectAllUserAndOrders();
}

Order:

package com.example.mpdemo.entity;import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;import java.util.List;
@TableName("orderss")
public class Order {@TableId(type= IdType.AUTO)private int id;private String orderTime;private int total;private int uid;//描述用户的所有订单 select id,username,password,orderss from user@TableField(exist = false)private User user;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getOrderTime() {return orderTime;}public void setOrderTime(String orderTime) {this.orderTime = orderTime;}public int getTotal() {return total;}public void setTotal(int total) {this.total = total;}public int getUid() {return uid;}public void setUid(int uid) {this.uid = uid;}public User getUser() {return user;}public void setUser(User user) {this.user = user;}@Overridepublic String toString() {return "Order{" +"id=" + id +", orderTime='" + orderTime + '\'' +", total='" + total + '\'' +", uid=" + uid +", user=" + user +'}';}
}

OrderController:

package com.example.mpdemo.controller;import com.example.mpdemo.mapper.OrderMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.apache.ibatis.annotations.Mapper;import javax.annotation.Resource;
import java.util.List;@RestController
public class OrderController {@Autowiredprivate OrderMapper orderMapper;@GetMapping("/order/findAll")public List findAll(){List orders=orderMapper.selectAllUserAndOrders();return orders;}
}

OrderMapper:

package com.example.mpdemo.mapper;import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.mpdemo.entity.Order;
import com.example.mpdemo.entity.User;
import org.apache.ibatis.annotations.*;import java.util.List;@Mapper
public interface OrderMapper extends BaseMapper<Order> {@Select("select * from orderss where uid=#{uid}")List<Order> selectByUid(int uid);//查询所有订单，同时查询订单的用户@Select("select * from orderss")@Results({@Result(column = "id",property = "id"),@Result(column = "orderTime",property = "orderTime"),@Result(column = "total",property = "total"),@Result(column = "uid",property = "user",javaType = User.class,//一个订单只能被一个用户拥有one=@One(select = "com.example.mpdemo.mapper.UserMapper.selectById" ))})List<User> selectAllUserAndOrders();
}

注意！！！！一直查不出order可以把表名字改成orderss。（因为order是sql的关键字）

测试：

2.条件查询

UserConrtroller中加入：

//条件查询@GetMapping("/user/find")public List<User> findByCond(){QueryWrapper<User> queryWrapper=new QueryWrapper();queryWrapper.eq("username","zhangsan");return userMapper.selectList(queryWrapper);}

测试：

3.分页查询（通过拦截器实现）

MyBatisPlusConfig：

package com.example.mpdemo.config;import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;@Configuration
public class MyBatisPlusConfig {@Beanpublic MybatisPlusInterceptor paginationInterceptor(){MybatisPlusInterceptor interceptor=new MybatisPlusInterceptor();//分页拦截器PaginationInnerInterceptor paginationInterceptor=new PaginationInnerInterceptor(DbType.MYSQL);//分页拦截器interceptor.addInnerInterceptor(paginationInterceptor);return interceptor;}}

测试：（从0开始，查两个记录）