【MyBatis】-----【MyBatis】---表级联系【一对一】--增删改查

一、核心配置文件

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 "http://mybatis.org/dtd/mybatis-3-config.dtd">
 <configuration>
      <!-- 最开始加载引用db.properties文件 -->
     <properties resource="db.properties"/>
     <!-- 取别名    以下情况别名为类名 -->
      <typeAliases>
          <package name="com.myBatis.entity"/>
      </typeAliases>
     <!--
         development : 开发模式
         work : 工作模式
      -->
     <environments default="development">
         <environment id="development">
             <transactionManager type="JDBC" />
             <!-- 配置数据库连接信息 -->
             <dataSource type="POOLED">
                 <property name="driver" value="${driver}" />
                 <property name="url" value="${url}" />
                 <property name="username" value="${username}" />
                 <property name="password" value="${password}" />
             </dataSource>
         </environment>
     </environments>
     <!-- 引用映射文件 -->
     <mappers >
         <mapper resource="com/myBatis/mapper/classesMapper.xml"/>
         <mapper resource="com/myBatis/mapper/teacherMapper.xml"/>
     </mappers>
 </configuration>

二、实体类

　　2.1Teacher

 package com.myBatis.entity;

 public class Teacher {
     // 定义实体类的属性，与teacher表中的字段对应
     private int id; // id===>t_id
     private String name; // name===>t_name
     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;
     }
     @Override
     public String toString() {
         return "Teacher [id=" + id + ", name=" + name + "]";
     }
     public Teacher() {
         super();
     }
     public Teacher(int id) {
         super();
         this.id = id;
     }

 }

　　2.2Classes

package com.myBatis.entity;

public class Classes {
    private int id; // id===>c_id
    private String name; // name===>c_name
    /**
     * class表中有一个teacher_id字段，所以在Classes类中定义一个teacher属性，
     * 用于维护teacher和class之间的一对一关系，通过这个teacher属性就可以知道这个班级是由哪个老师负责的
     */
    private Teacher teacher;
    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 Teacher getTeacher() {
        return teacher;
    }
    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }
    @Override
    public String toString() {
        return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + "]";
    }
    public Classes(String name, Teacher teacher) {
        super();
        this.name = name;
        this.teacher = teacher;
    }
    public Classes() {
        super();
    }

}

三、映射文件

teacherMapper.xml

 <?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">
     <!--
     为这个mapper指定一个唯一的namespace，namespace的值习惯上设置成包名+sql映射文件名，
     这样就能够保证namespace的值是唯一的
     -->
     <mapper namespace="com.myBatis.mapper.teacherMapper">
         <!-- 根据id查询得到一个user对象 -->
         <select id="getteacher" parameterType="int" resultMap="TeacherResultMap">
             select * from classes c, teacher t where c.t_id=t.t_id and t.t_id=#{id}
         </select>
         <!-- 使用resultMap映射实体类和字段之间的一一对应关系 -->
         <resultMap type="teacher" id="TeacherResultMap">
             <id property="id" column="t_id"/>
             <result property="name" column="t_name"/>
         </resultMap>

          <insert id="addTeacher" parameterType="Teacher">
             insert into teacher values(#{t_name})
         </insert>

     </mapper>
     

classesMapper.xml

 <?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">
     <!--
     为这个mapper指定一个唯一的namespace，namespace的值习惯上设置成包名+sql映射文件名，
     这样就能够保证namespace的值是唯一的
     -->
     <mapper namespace="com.myBatis.mapper.classesMapper">
     <!-- 嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集
              封装联表查询的数据(去除重复的数据)
              根据id查询得到一个user对象 -->
         <select id="getclassess" parameterType="int" resultMap="ClassResultMap">
              select * from classes c, teacher t where c.t_id=t.t_id and c.c_id=#{id}
         </select>
         <!-- 使用resultMap映射实体类和字段之间的一一对应关系 -->
         <resultMap type="Classes" id="ClassResultMap">
             <id property="id" column="c_id"/>
             <result property="name" column="c_name"/>
             <association property="teacher" javaType="Teacher">
                 <id property="id" column="t_id"/>
                 <result property="name" column="t_name"/>
             </association>
         </resultMap>
         <!--  根据id查询删除一个class 的t_id -->
         <delete id="deleteClasses" parameterType="Classes">
             delete from classes where c_id=#{id}
         </delete>
           <!-- 添加(Create) -->
         <insert id="addClasses" parameterType="Classes">
             insert into classes values(null,#{name},#{teacher.id})
         </insert>
          <!-- 修改班级所对应的老师(Update) -->
         <update id="updateClasses" parameterType="Classes">
             update classes set t_id=#{teacher.id} where c_id=#{id}
         </update>

     </mapper>
     

四、测试类

 package myBatisTest;
 import org.apache.ibatis.session.SqlSession;
 import org.junit.Test;

 import com.myBatis.entity.Classes;
 import com.myBatis.entity.Teacher;
 import com.myBatis.util.myBtaisUtil;

 public class TestUser {
     //修改
     @Test
     public void testUpdateClasses() {
         SqlSession sqlSession=myBtaisUtil.getsqlSession();
         //先查找
         String selectclasses = "com.myBatis.mapper.classesMapper.getclassess";
         Classes classes =sqlSession.selectOne(selectclasses, 3);
         System.out.println(classes);
          //再修改
         Teacher teacher = new Teacher(4);
         System.out.println();
         classes.setTeacher(teacher);
         String update = "com.myBatis.mapper.classesMapper.updateClasses";
         int i = sqlSession.update(update, classes);
          System.out.println(i);
          Classes  classes2= sqlSession.selectOne(selectclasses, 3);
          System.out.println(classes2);
     }

       //添加
     @Test
     public void testAddClasses() {
         SqlSession sqlSession=myBtaisUtil.getsqlSession();
          String add = "com.myBatis.mapper.classesMapper.addClasses";
          Classes classes = new Classes();
          Teacher teacher= new Teacher(4);
          classes.setName("1111");
          classes.setTeacher(teacher);
          int i = sqlSession.insert(add, classes);
          System.out.println(i);
     }

     //删除
     @Test
     public void testDeleteClasses() {
         SqlSession sqlSession=myBtaisUtil.getsqlSession();
         String delete = "com.myBatis.mapper.classesMapper.deleteClasses";
         int i= sqlSession.delete(delete, 5);
         System.out.println(i);
     }

     //查询
     @Test
     public void testGetClasses() {
         SqlSession sqlSession=myBtaisUtil.getsqlSession();
         String select = "com.myBatis.mapper.classesMapper.getclassess";
         Classes classes = sqlSession.selectOne(select, 7);
         System.out.println(classes);
     }
 }

MyBatis一对一关联查询总结

　　MyBatis中使用association标签来解决一对一的关联查询，association标签可用的属性如下：

• property:对象属性的名称
• javaType:对象属性的类型
• column:所对应的外键字段名称
• select:使用另一个查询封装的结果

参考：MyBatis学习总结(五)——实现关联表查询