mybatis11–多对多关联查询详解编程语言

/** 
 *学生对应的实体类 
 */ 
public class Student { 
     
    private  Integer sId; 
    private  String sName; 
    //一个学生可以有多个老师 
    private Set<Teacher> teachers=new HashSet<Teacher>(); 
     
    public Integer getsId() { 
        return sId; 
    } 
    public void setsId(Integer sId) { 
        this.sId = sId; 
    } 
    public String getsName() { 
        return sName; 
    } 
    public void setsName(String sName) { 
        this.sName = sName; 
    } 
    public Set<Teacher> getTeachers() { 
        return teachers; 
    } 
    public void setTeachers(Set<Teacher> teachers) { 
        this.teachers = teachers; 
    } 
    public Student(Integer sId, String sName, Set<Teacher> teachers) { 
        super(); 
        this.sId = sId; 
        this.sName = sName; 
        this.teachers = teachers; 
    } 
    public Student() { 
        super(); 
    } 
    //在双向关联的时候    只能一方显示关联信息   否则会出现stackOverflow 异常 
    @Override 
    public String toString() { 
        return "Student [sId=" + sId + ", sName=" + sName + ", teachers=" 
                + teachers + "]"; 
    } 
     
 
}

/** 
 *老师的实体类 
 */ 
public class Teacher { 
    private  Integer tId; 
    private  String tName; 
     //一个老师可以有多个学生 
    private  Set<Student> students=new HashSet<Student>(); 
    public Integer gettId() { 
        return tId; 
    } 
    public void settId(Integer tId) { 
        this.tId = tId; 
    } 
    public String gettName() { 
        return tName; 
    } 
    public void settName(String tName) { 
        this.tName = tName; 
    } 
    public Set<Student> getStudents() { 
        return students; 
    } 
    public void setStudents(Set<Student> students) { 
        this.students = students; 
    } 
    public Teacher(Integer tId, String tName, Set<Student> students) { 
        super(); 
        this.tId = tId; 
        this.tName = tName; 
        this.students = students; 
    } 
    public Teacher() { 
        super(); 
    } 
    @Override 
    public String toString() { 
        return "Teacher [tId=" + tId + ", tName=" + tName + ", students=" 
                + students.size() + "]"; 
    } 
     
}

public interface StudentDao { 
    /** 
     * 根据学生的编号查询所有对应老师信息 
     */ 
    Student selectTeahcerById(Integer tId); 
}

<?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"> 
<mapper namespace="cn.bdqn.dao.StudentDao"> 
 
    <resultMap type="Student" id="studentMap"> 
          <id property="sId" column="sid"/> 
          <result property="sName" column="sname"/> 
      <!-- 设置关联集合的属性  --> 
      <collection property="teachers" ofType="Teacher"> 
          <id property="tId" column="tid"/> 
          <result property="tName" column="tname"/> 
      </collection> 
    </resultMap> 
  
    <!-- 根据学生的编号查询所有对应老师信息 --> 
     <select id="selectTeahcerById" resultMap="studentMap"> 
      select  sid,sname,tid,tname from  student,middle,teacher 
         where  sid=studentId and tid=teacherId and sid=#{xxx} 
    </select> 
     
</mapper>

    <!-- 加载映射文件信息 --> 
    <mappers> 
        <mapper resource="cn/bdqn/dao/StudentMapper.xml" /> 
    </mappers>

public class TeacherTest { 
    StudentDao dao; 
    SqlSession session; 
 
    @Before 
    public void before() { 
        // 因为需要关闭session 需要把session提取出去 
        session = SessionUtil.getSession(); 
        dao = session.getMapper(StudentDao.class); 
    } 
 
    @After 
    public void after() { 
        if (session != null) { 
            session.close(); 
        } 
    } 
 
    /** 
     * 根据老师的编号查询所有的导师信息 
     */ 
    @Test 
    public void test1() { 
        Student student = dao.selectTeahcerById(1); 
        System.out.println(student); 
    } 
     
}