多
对一：多个tid对应一个id，可以简单理解多个学生对应一个老师这种类型。
一对多: 一个id对应多个tid,可以简单理解一个老师对应多个学生这种类型。
多对一和一对多都可以通过查询嵌套处理和结果嵌套处理。
多对一：
1.创建简单的环境。（坐标导包，类，接口，主配置文件，映射配置文件）
类中的setter and getter, toString 方法可以通过@Data 简化daiti,前提是导入lombok坐标
主配置文件中 可以通过<propertis resource="配置文件名">引入外部配置文件。
<typeAliases> 可以通过两种方式（<typeAlias type="全限定类名" alias="别名"/>； <package name="包名"/>）配置别名
<mapper> 可以通过两种方式（resource=xx/xx.xml 映射配置文件中写sql； class=xx.xx.接口，接口上写注释sql）
2.接口中编写代码
public interface IStudent {
ListfindAll();
ListgetStudent();
}
3.映射配置文件中写sql
<mapper namespace="com.dao.IStudent">
<!--================按照查询嵌套处理================-->
<select id="findAll" resultMap="StudentTeacher">
select* from student;
<resultMap id="StudentTeacher" type="Student">
<result property="id" column="id"/>
<result property="name" column="name"/>
<!--复杂的对象我们需要单独处理 对象：association 集合：collection-->
<association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
<select id="getTeacher" resultType="Teacher">
select* from teacher where id=#{id}
<!--**************按照结果嵌套处理*******************-->
<select id="getStudent" resultMap="StudentTeacher2">
select s.id sid,s.name sname,t.name tname from student s, teacher t where s.tid = t.id
<resultMap id="StudentTeacher2" type="Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<association property="teacher" column="tname" javaType="Teacher">
<result property="name" column="tname"/>
</mapper>
4.编写测试类
@Test
public void testStudent(){
IStudent mapper =sqlSession.getMapper(IStudent.class);
List studentList = mapper.findAll();
for(Student student : studentList){
System.out.println(student);
}
}
@Test
public void testStudent2(){
IStudent mapper =sqlSession.getMapper(IStudent.class);
List studentList = mapper.getStudent();
for(Student student : studentList){
System.out.println(student);
}
}
一对多：
1.同上。
2.编写接口
public interface TeacherMapper {
Teacher1getTeacher(@Param("tid")int id);
Teacher1getTeacher2(@Param("tid")int id);
}
3.编写映射配置文件
<mapper namespace="com.dao.TeacherMapper">
<!--===================结果嵌套处理（引用别名）===============-->
<select id="getTeacher" resultMap="TeacherStudent">
select s.id sid, s.name sname, t.id tid, t.name tname from student s, teacher t where s.tid=t.id and t.id= #{tid};
<resultMap id="TeacherStudent" type="Teacher1">
<result property="id" column="tid"/>
<result property="name" column="tname"/>
<collection property="students" ofType="Student1">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<result property="tid" column="tid"/>
<!--====================查询嵌套处理=================-->
<select id="getTeacher2" resultMap="TeacherStudent1">
select * from teacher where id=#{tid};
<resultMap id="TeacherStudent1" type="Teacher1">
<collection property="students" javaType="ArrayList" ofType="Student1" column="id" select="getStudentsByID"/>
<select id="getStudentsByID" resultType="Student1">
select * from student where tid=#{tid}
</mapper>
4.编写测试类
public class TestAll {
private SqlSessionsqlSession;
private InputStreamin;
@Before
public void init()throws IOException {
//1.读取配置文件，生成字节输入流
in = Resources.getResourceAsStream("MybatisConfig.xml");
//2.获取sqlSessionFactory
SqlSessionFactory factory =new SqlSessionFactoryBuilder().build(in);
//3.获取sqlSession对象
sqlSession = factory.openSession();
}
@After
public void destroy()throws IOException {
//6.释放资源
sqlSession.close();
in.close();
}
@Test
public void testGetTeacherById(){
TeacherMapper mapper =sqlSession.getMapper(TeacherMapper.class);
Teacher1 teacher = mapper.getTeacher(1);
System.out.println(teacher);
}
@Test
public void testGetTeacherById2(){
TeacherMapper mapper =sqlSession.getMapper(TeacherMapper.class);
Teacher1 teacher = mapper.getTeacher2(1);
System.out.println(teacher);
}
}
