学步园

在学习MyBatis3的过程中，文档上面一直在强调一个id的东西！在做这个实验的时候，也因为没有理解清楚id含义而导致一对多的“多”中也只有一条数据。id和result的唯一不同是id表示的结果将是当比较对象实例时用到的标识属性。这帮助来改进整体表现，特别是缓存和嵌入结果映射。所以不同数据的id应该唯一区别，不然倒置数据结果集只有一条数据。

TeacherMapper.xml

<?xml version="1.0" encoding="UTF-8"?><br /> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"><br /> <mapper namespace="com.nantian.mybatis.one2many.TeacherMapper"><br /> <resultMap type="Teacher" id="teacher"><br /> <id property="id" column="t_id" javaType="int" jdbcType="INTEGER"/><br /> <result property="name" column="t_name" javaType="string" jdbcType="VARCHAR"/><br /> <collection property="students" column="t_s_id" ofType="Student"><br /> <id property="id" column="s_id" javaType="int" jdbcType="INTEGER"/><br /> <result property="name" column="s_name" javaType="string" jdbcType="VARCHAR"/><br /> </collection><br /> </resultMap></p> <p> <select id="one2many" parameterType="int" resultMap="teacher"><br /> select t.t_id,t.t_name,s.t_s_id,s.s_id,s.s_name<br /> from teacher t join student s on t.t_id = s.t_s_id where t.t_id = #{id}<br /> </select><br /> </mapper>

Teacher

package com.nantian.mybatis.one2one;</p> <p>import java.util.List;</p> <p>import com.nantian.mybatis.one2many.Student;</p> <p>public class Teacher {<br /> private int id;<br /> private String name;<br /> private List<Student> students;</p> <p> public int getId() {<br /> return id;<br /> }</p> <p> public void setId(int id) {<br /> this.id = id;<br /> }</p> <p> public String getName() {<br /> return name;<br /> }</p> <p> public void setName(String name) {<br /> this.name = name;<br /> }</p> <p> public List<Student> getStudents() {<br /> return students;<br /> }</p> <p> public void setStudents(List<Student> students) {<br /> this.students = students;<br /> }<br /> }

TeacherMapper

package com.nantian.mybatis.one2many;</p> <p>import com.nantian.mybatis.one2one.Teacher;</p> <p>public interface TeacherMapper {<br /> public Teacher one2many(int id);<br /> }

Student

package com.nantian.mybatis.one2many;</p> <p>public class Student {<br /> private int id;<br /> private String name;</p> <p> public int getId() {<br /> return id;<br /> }</p> <p> public void setId(int id) {<br /> this.id = id;<br /> }</p> <p> public String getName() {<br /> return name;<br /> }</p> <p> public void setName(String name) {<br /> this.name = name;<br /> }<br /> }

T

package com.nantian.mybatis.one2many;</p> <p>import java.util.List;</p> <p>import org.apache.ibatis.session.SqlSession;</p> <p>import com.nantian.mybatis.data.DBUtil;<br /> import com.nantian.mybatis.one2one.Teacher;</p> <p>public class T {</p> <p> public static void main(String[] args) {<br /> SqlSession sqlSession = DBUtil.getInstance().getSqlSessionFactory()<br /> .openSession();<br /> try {<br /> TeacherMapper teacherMapper = sqlSession<br /> .getMapper(TeacherMapper.class);<br /> Teacher teacher = teacherMapper.one2many(100);<br /> List<Student> students = teacher.getStudents();<br /> System.out.println(teacher.getId());<br /> System.out.println(teacher.getName());<br /> for (Student student : students) {<br /> System.out.println(student.getId());<br /> System.out.println(student.getName());<br /> }<br /> } finally {<br /> sqlSession.close();<br /> }<br /> }</p> <p>}