目录

二、多对一的注解查询

1.多对一立即加载查询

2.多对一延迟加载查询

二、多对一的注解查询

1.多对一立即加载查询

①.StudentDao接口的方法编写

@Select(" SELECT  student.*,teacher.Tname FROM student LEFT JOIN teacher  on student.t_id = teacher.id")
@Results(value = {
        @Result(property = "id",column = "id"),
        @Result(property = "Sname",column = "Sname"),
        @Result(property = "sex",column = "sex"),
        @Result(property = "age",column = "age"),
        @Result(property = "t_id",column = "t_id"),
        @Result(property = "teacher.Tname",column = "Tname")
})
public List getStudent();

②.进行测试

@Test
public void getStudent(){
    List student = mapper.getStudent();
    for (Student student1:student) {
        System.out.println(student1.toString());
    }
}

2.多对一延迟加载查询

①.StudentDao接口的方法编写

@Select("select * from student")
@Results(value = {
        @Result(property = "id",column = "id"),
        @Result(property = "Sname",column = "Sname"),
        @Result(property = "sex",column = "sex"),
        @Result(property = "age",column = "age"),
        @Result(property = "teacher",column = "t_id",one=@One(select = "com.qcby.dao.TeacherDao.getTeacher",fetchType = FetchType.LAZY))
})
public List getStudent();

②.TeacherDao接口的方法编写

@Select("select  * from  teacher where id = #{t_id}")
Teacher getTeacher(Integer id);

③.进行测试

@Test
public void getStudent(){
    List student = mapper.getStudent();
    for (Student student1:student) {
        System.out.println(student1.toString());
    }
}