4、SpringBoot+Mybatis整合------一对多

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开发工具：STS

代码下载链接：https://github.com/theIndoorTrain/SpringBoot_Mybatis/tree/c00b56dbd51a1e26ab9fd990201ad9e89a770ca9

前言：

今天探讨的是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：

二、代码实现：

1.添加Book实体：

 package com.xm.pojo;

 /**

  * 书的实体

  * @author xm

  *

  */

 public class Book {

     private int id;

     private int sid;

     private String name;

     private double price;

     public int getId() {

         return id;

     }

     public void setId(int id) {

         this.id = id;

     }

     public int getSid() {

         return sid;

     }

     public void setSid(int sid) {

         this.sid = sid;

     }

     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Student实体中添加book集合：

 package com.xm.pojo;

 import java.util.List;

 /**

  * name:学生实体

  * @author xxm

  *

  */

 public class Student {

     /**

      * content:主键id

      */

     private int id;

     /**

      * content:姓名

      */

     private String name;

     private List<Book> books;

     public Student() {

         // TODO Auto-generated constructor stub

     }

     public List<Book> getBooks() {

         return books;

     }

     public void setBooks(List<Book> books) {

         this.books = books;

     }

     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;

     }

 }

Student.java

3.在StudentMapper接口中定义查询方法：

 package com.xm.mapper;

 import java.util.List;

 import com.xm.pojo.Student;

 public interface StudentMapper {

     /**

      * 根据id查询

      * @param id

      * @return

      */

     public Student getById(Integer id);

     /**

      * 查询全部

      * @return

      */

     public List<Student> list();

     /**

      * 插入

      * @param student

      */

     public int insert(Student student);

     /**

      * 主键回填的插入

      * @param student

      * @return

      */

     public int insertToId(Student student);

     /**

      * 根据student的id修改

      * @param student

      */

     public void update(Student student);

     /**

      * 根据id删除

      * @param id

      */

     public void delete(Integer id);

     /**

      * 根据id查询所有的书

      * @param id

      */

     public Student selectBookById(Integer id);

 }

StudentMapper.java

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.xm.mapper.StudentMapper">

     <!-- 根据id查询 -->

     <select id="getById" parameterType="int" resultType="student">

     select * from student where id=#{id}

     </select>

     <!-- 查询所有 -->

     <select id="list" parameterType="int" resultType="student">

     select * from student

     </select>

     <!-- 插入一个学生 -->

     <insert id="insert" parameterType="student">

     insert into student(name) values(#{name})

     </insert>

     <!-- 主键回填的插入 -->

     <insert id="insertToId" parameterType="student" useGeneratedKeys="true" keyProperty="id">

     insert into student(name) values(#{name})

     </insert>

     <!-- 根据id修改学生信息 -->

     <update id="update" parameterType="student">

     update student set name=#{name} where id=#{id}

     </update>

     <!-- 根据id删除学生 -->

     <delete id="delete" parameterType="int">

     delete  from student where id=#{id}

     </delete>

     <resultMap type="student" id="bookMap">

         <id property="id" column="id"/>

         <result property="name" column="name"/>

         <collection property="books" ofType="book">

             <id property="id" column="bid"/>

             <result property="name" column="bname"/>

             <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 bname,b.price from student a,book b where a.id=b.sid and a.id=#{id};

     </select>

 </mapper>

StudentMapper.xml

5.在StudentController中实现查询：

 package com.xm.controller;

 import java.util.List;

 import javax.websocket.server.PathParam;

 import org.springframework.beans.factory.annotation.Autowired;

 import org.springframework.web.bind.annotation.DeleteMapping;

 import org.springframework.web.bind.annotation.GetMapping;

 import org.springframework.web.bind.annotation.PathVariable;

 import org.springframework.web.bind.annotation.PostMapping;

 import org.springframework.web.bind.annotation.PutMapping;

 import org.springframework.web.bind.annotation.RestController;

 import com.xm.mapper.StudentMapper;

 import com.xm.pojo.Student;

 @RestController

 public class StudentController {

     @Autowired

     private StudentMapper studentMapper;

     /**

      * 根据id查询学生

      * @param id

      * @return

      */

     @GetMapping("/student/{id}")

     public Student getById(@PathVariable("id") Integer id) {

         Student student = studentMapper.getById(id);

         return student;

     }

     /**

      * 查询全部

      * @return

      */

     @GetMapping("/students")

     public List<Student> list(){

         List<Student> students = studentMapper.list();

         return students;

     }

     /**

      * 插入

      * @param student

      */

     @PostMapping("/student")

     public void insert( Student student) {

         studentMapper.insert(student);

     }

     /**

      * 修改

      * @param student

      */

     @PutMapping("/student/{id}")

     public void update(Student student,@PathVariable("id")Integer id) {

         studentMapper.update(student);

     }

     /**

      * 根据id删除

      * @param id

      */

     @DeleteMapping("/student/{id}")

     public void delete(@PathVariable("id") Integer id) {

         studentMapper.delete(id);

     }

     /**

      * 根据id查询所有的书

      */

     @GetMapping("/student/book/{id}")

     public Student getBooks(@PathVariable("id") Integer id) {

         Student student = studentMapper.selectBookById(id);

         return student;

     }

 }