上一章说了多对一，很多学生被一个老师教，这一章是一个老师教很多学生
目录基本没有变化只是改了配置文件：
2、配置文件：
TeacherMapper接口类：
package com.hdlf.dao; import com.hdlf.pojo.student;
import com.hdlf.pojo.teacher; import java.util.List; public interface TeacherMapper {
//方式一
teacher getteacher(int tid);
//方式二
teacher getteacher2(int tid); }
teacher实体类：
package com.hdlf.pojo;
import lombok.Data;
import java.util.List;
public class teacher {
private int tid;
private String tname;
//因为需要获取到学生所以在这里加一个List泛型集合
List<student> students;
public List<student> getStudents() {
return students;
}
public void setStudents(List<student> students) {
this.students = students;
}
public teacher() {
}
public teacher(int tid, String tname, List<student> students) {
this.tid = tid;
this.tname = tname;
this.students = students;
}
public int getTid() {
return tid;
}
public void setTid(int tid) {
this.tid = tid;
}
public String getTname() {
return tname;
}
public void setTname(String tname) {
this.tname = tname;
}
@Override
public String toString() {
return "teacher{" +
"tid=" + tid +
", tname='" + tname + '\'' +
", students=" + students +
'}';
}
}student实体类因为是根据老师查教过多少学生，学生类不用写特别的类：
package com.hdlf.pojo;
public class student {
private int sid;
private String sname;
private int tid;
@Override
public String toString() {
return "student{" +
"sid=" + sid +
", sname='" + sname + '\'' +
", tid=" + tid +
'}';
}
public int getSid() {
return sid;
}
public void setSid(int sid) {
this.sid = sid;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
public int getTid() {
return tid;
}
public void setTid(int tid) {
this.tid = tid;
}
public student(int sid, String sname, int tid) {
this.sid = sid;
this.sname = sname;
this.tid = tid;
}
public student() {
}
}TeacherMapper.xml配置类:
这个是方式一：
复杂的属性，需要单独处理 对象使用：association
集合使用：collection
javaType 指定属性类型，集合中泛型信息使用ofType获取
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.hdlf.dao.TeacherMapper"> <select id="getteacher" resultMap="getstudent">
select t.tid, t.tname ,s.sname,s.sid from student s,teacher t where s.tid = t.tid and t.tid = #{tid};
</select> <resultMap id="getstudent" type="teacher">
<result property="tid" column="tid"></result>
<result property="tname" column="tname"></result> <!--复杂的属性，需要单独处理 对象：association 集合：collection
javaType 指定属性类型
集合中泛型信息使用ofType获取
这个studens就是teacher实体类中的students-->
<collection property="students" ofType="student">
<result property="sid" column="sid"></result>
<result property="sname" column="sname"></result>
</collection> </resultMap>
</mapper>
测试结果：
teacher{tid=0, tname='王老师', students=[student{sid=1, sname='张三', tid=1}, student{sid=2, sname='李四', tid=1}, student{sid=3, sname='王五', tid=1}, student{sid=4, sname='吴六', tid=1}, student{sid=5, sname='赵七', tid=1}]}方式二个人理解其实都一样：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.hdlf.dao.TeacherMapper">
<select id="getteacher2" resultMap="getallteacher">
select * from mybatis.teacher where tid = #{tid}
</select>
<resultMap id="getallteacher" type="teacher">
<collection property="students" select="getallstudent" javaType="ArrayList" ofType="studnet" column="tid"></collection>
</resultMap>
<select id="getallstudent" resultType="student">
select * from mybatis.student;
</select> </mapper>
这个就是一对多的处理，小编还是没有领悟到其中的精髓，希望过几天可以顿悟。