mybatis09–自连接一对多查询详解编程语言

/** 
 *导师的实体类 
 */ 
public class Teacher { 
    private  Integer id; 
    private  String name; 
     //导师下所有的老师 
    private  Set<Teacher> teachers; 
     
    public Integer getId() { 
        return id; 
    } 
    public void setId(Integer id) { 
        this.id = id; 
    } 
    public String getName() { 
        return name; 
    } 
    public void setName(String name) { 
        this.name = name; 
    } 
    public Set<Teacher> getTeachers() { 
        return teachers; 
    } 
    public void setTeachers(Set<Teacher> teachers) { 
        this.teachers = teachers; 
    } 
    public Teacher(Integer id, String name, Set<Teacher> teachers) { 
        super(); 
        this.id = id; 
        this.name = name; 
        this.teachers = teachers; 
    } 
    public Teacher() { 
        super(); 
    } 
    @Override 
    public String toString() { 
        return "Teacher [id=" + id + ", name=" + name + ", teachers=" 
                + teachers + "]"; 
    } 
}

public interface TeacherDao { 
    /** 
     * 根据导师的编号查询所有的老师信息  
     * 相当于递归查询  
     */ 
    List<Teacher> selectTeahcerByTid(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.TeacherDao"> 
 
 
 
 
    <resultMap type="Teacher" id="teacherMap"> 
      <id property="id" column="id"/> 
      <result property="name" column="name"/> 
      <!-- 设置关联集合的属性  
       select="selectTeahcerByTid" 
                   因为查询的结果都是一样的   递归查询 
       column="id" 
                 根据查询到的id再作为参数进行下一次的查询 
       --> 
      <collection property="teachers" ofType="Teacher" 
       select="selectTeahcerByTid" column="id"/> 
    </resultMap> 
  
     <select id="selectTeahcerByTid" resultMap="teacherMap"> 
      select  id,name from  teacher where tid=#{xxx} 
    </select> 
     
</mapper>

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

package cn.bdqn.test; 
 
import java.util.ArrayList; 
import java.util.HashMap; 
import java.util.List; 
import java.util.Map; 
 
import org.apache.ibatis.session.SqlSession; 
import org.junit.After; 
import org.junit.Before; 
import org.junit.Test; 
 
import cn.bdqn.bean.Teacher; 
import cn.bdqn.dao.TeacherDao; 
import cn.bdqn.util.SessionUtil; 
 
public class TeacherTest { 
    TeacherDao 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(TeacherDao.class); 
    } 
 
    @After 
    public void after() { 
        if (session != null) { 
            session.close(); 
        } 
    } 
 
    /** 
     * 根据导师的id查询出对应的所有老师信息 
     */ 
    @Test 
    public void test1() { 
        List<Teacher> list = dao.selectTeahcerByTid(1); 
        for (Teacher teacher : list) { 
            System.out.println(teacher); 
        } 
    } 
     
}

public interface TeacherDao { 
    /** 
     * 根据导师的编号查询所有的老师信息以及自身的信息  
     */ 
    Teacher 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.TeacherDao"> 
 
   <select id="selectTeahcerByTid" resultMap="teacherMap"> 
     select id,name from teacher where tid=#{xxx} 
     <!--#{xxx} 就是再根据tid查询对应的子项 --> 
   </select> 
 
    <resultMap type="Teacher" id="teacherMap"> 
      <id property="id" column="id"/> 
      <result property="name" column="name"/> 
      <!-- 设置关联集合的属性  
       select="selectTeahcerByTid" 
                   因为查询的结果都是一样的   递归查询 
       column="id" 
                 根据查询到的id再作为tid进行下一次的查询 
       --> 
      <collection property="teachers" ofType="Teacher" 
       select="selectTeahcerByTid" column="id"/> 
    </resultMap> 
  
     <select id="selectTeahcerById" resultMap="teacherMap"> 
          <!--先查询出 自身的信息  --> 
      select  id,name from  teacher where id=#{xxx} 
    </select> 
     
</mapper>

    /** 
     * 根据导师的id查询出对应的所有老师信息 
     */ 
    @Test 
    public void test1() { 
        Teacher teacher = dao.selectTeahcerById(1); 
            System.out.println(teacher); 
        }