3.SpringBoot整合Mybatis(一对多)

前言：

　　Mybatis一对多的处理关系：

一个人有好多本书，每本书的主人只有一个人。当我们查询某个人拥有的所有书籍时，就涉及到了一对多的映射关系。

一、添加数据表：

 CREATE TABLE `book` (
   `id` int(6) NOT NULL,
   `name` varchar(50) DEFAULT NULL,
   `uid` int(6) DEFAULT NULL,
   `price` double DEFAULT NULL,
   PRIMARY KEY (`id`),
   KEY `bu_id` (`uid`),
   CONSTRAINT `bu_id` FOREIGN KEY (`uid`) REFERENCES `user` (`id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

二、代码实现：

1.添加Book实体：

 package com.beilin.entity;
 /*
    * 书的实体
    * @author 北林
    *
    */

 public class Book {

     private int id;
     private int uid;
     private String name;
     private double price;

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public int getUid() {
         return uid;
     }

     public void setUid(int uid) {
         this.uid = uid;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public double getPrice() {
         return price;
     }

     public void setPrice(double price) {
         this.price = price;
     }
 }

Book.java

2.在User实体中添加book集合：

 public class User {
     /**
      *  name:学生实体
      */

     //主键id
     private int id;
     //姓名
     private String name;
     //年龄
     private int age;
     //添加book集合
     private List<Book> books;

     // Get和 Set方法
     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public int getAge() {
         return age;
     }

     public void setAge(int age) {
         this.age = age;
     }

     public List<Book> getBooks() {
         return books;
     }

     public void setBooks(List<Book> books) {
         this.books = books;
     }
 }

User.java

3.在UserMapper接口中定义查询方法：

 package com.beilin.mapper;

 import com.beilin.entity.User;

 import java.util.List;

 public interface UserMapper {

      //插入
     public void insert(User user);

     //根据id删除
     public void delete(Integer id);

      //根据user的id修改
     public void update(User user);

     //根据id查询
     public User getById(Integer id);

     //查询全部
     public List<User> list();

     /**
           * 根据id查询所有的书
            * @param id
           */
     public User selectBookById(Integer id);

 }

UserMapper

4.在mapper映射关系中，添加一对多的select和resaultMap：

注意：当多个表的字段名一样的时候，查询需要用别名

 <?xml version="1.0" encoding="UTF-8"?>
         <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 <mapper namespace="com.beilin.mapper.UserMapper">

 <!-- 插入一个user -->
 <insert id="insert" parameterType="user" useGeneratedKeys="true" keyProperty="id">
         insert into user(name,age) values(#{name},#{age})
     </insert>

 <!-- 根据id删除user -->
 <delete id="delete" parameterType="int">
         delete  from user where id=#{id}
     </delete>

 <!-- 根据id修改user信息 -->
 <update id="update" parameterType="user">
         update user set name=#{name},age=#{age} where id=#{id}
     </update>

 <!-- 根据id查询 -->
 <select id="getById" parameterType="int" resultType="user">
         select * from user where id=#{id}
     </select>

 <!-- 查询所有 -->
 <select id="list" parameterType="int" resultType="user">
         select * from user
     </select>

 <resultMap id="bookMap" type="user">
     <id property="id" column="id"/>
     <result property="name" column="name"/>
     <result property="age" column="age"/>
     <collection property="books" ofType="book">
         <id property="id" column="bid"/>
         <result property="name" column="bookName"/>
         <result property="price" column="price"/>
     </collection>
 </resultMap>

 <!--根据id查询所有的书  -->
 <select id="selectBookById" parameterType="int" resultMap="bookMap">
         select a.*,b.id bid,b.name as "bookName"  ,b.price from user a,book b where a.id=b.uid and a.id=#{id};
     </select>

 </mapper>

UserMapper.xml

5.在UserController中实现查询：

 package com.beilin.controller;

 import com.beilin.entity.Book;
 import com.beilin.entity.User;
 import com.beilin.mapper.UserMapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.web.bind.annotation.*;

 import java.util.List;

 @RestController
 public class UserController {

     @Autowired
     private UserMapper userMapper;

         //插入user
     @RequestMapping("/user")
     public void insert( User user) {
         userMapper.insert(user);
     }

       //根据id删除
     @RequestMapping("/user1/{id}")
     public void delete(@PathVariable("id") Integer id) {
         userMapper.delete(id);
     }
         //修改
     @RequestMapping("/user2/{id}")
     public void update(User user,@PathVariable("id") Integer id) {
         userMapper.update(user);
     }

      //根据id查询user
     @RequestMapping("/user3/{id}")
     public User getById(@PathVariable("id") Integer id) {
         User user = userMapper.getById(id);
         return user;
     }

     //查询全部
     @RequestMapping("/users")
     public List<User> list(){
         List<User> users = userMapper.list();
         return users;
     }

     /**
           * 根据id查询所有的书
            */
     @GetMapping("/user/book/{id}")
     public User getBooks(@PathVariable("id") Integer id){
         User user = userMapper.selectBookById(id);
         return user;
     }
 }

UserController.java

三、测试结果：

1.数据库查询结果：

2.postman访问结果：