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[ASP.net教程]Mybatis框架中实现双向一对多关系映射


学习过Hibernate框架的伙伴们很容易就能简单的配置各种映射关系(Hibernate框架的映射关系在我的blogs中也有详细的讲解),但是在Mybatis框架中我们又如何去实现

一对多的关系映射呢? 其实很简单

首先我们照常先准备前期的环境(具体解释请  参考初识Mybatis进行增、删、改、查 blogs )这里我就直接上代码了

主配置文件:Configuration.

<?"1.0" encoding="UTF-8" ?><!DOCTYPE configuration  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"  "http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration> <environments default="development">  <environment id="development">   <transactionManager type="JDBC">    <property name="" value=""/>   </transactionManager>   <dataSource type="UNPOOLED">    <property name="driver" value="oracle.jdbc.OracleDriver"/>    <property name="url" value="jdbc:oracle:thin:@localhost:1521:orcl"/>    <property name="username" value="practice"/>    <property name="password" value="123"/>   </dataSource>  </environment> </environments>   <mappers>  <mapper resource="config/Student."/>  <mapper resource="config/Grade."/> </mappers> </configuration>

 

背景:学生和班级是一个典型的一对多的关系,一个班级可以对应着多个学生,所以我们随即创建了学生对象和班级对象

学生类:Student

package entity;/* * 学生类 * */public class Student {  //学生编号  private Integer sid;  //学生名称  private String sname;  //学生性别  private String sex;    public Student() {  }  public Student(String sname, String sex) {    this.sname = sname;    this.sex = sex;  }  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 String getSex() {    return sex;  }  public void setSex(String sex) {    this.sex = sex;  }  }

 

班级类:Grade

package entity;import java.util.HashSet;import java.util.Set;/* * 班级类 * */public class Grade {  //班级编号  private Integer gid;  //班级名称  private String gname;  //班级描述  private String gdesc;  //班级下的学生信息  private Set<Student> stus=new HashSet<Student>();    public Set<Student> getStus() {    return stus;  }  public void setStus(Set<Student> stus) {    this.stus = stus;  }  public Grade() {  }  public Grade(Integer gid, String gname, String gdesc) {    this.gid = gid;    this.gname = gname;    this.gdesc = gdesc;  }  public Integer getGid() {    return gid;  }  public void setGid(Integer gid) {    this.gid = gid;  }  public String getGname() {    return gname;  }  public void setGname(String gname) {    this.gname = gname;  }  public String getGdesc() {    return gdesc;  }  public void setGdesc(String gdesc) {    this.gdesc = gdesc;  }  }

实体类准备完了的话,我们就可以开始看配置文件了,也是最关键的一部分

首先讲简单点的学生实体类对应的配置文件

Student.

<?"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="Student"> <resultMap type="entity.Student" id="StudentResult">  <id column="sid" jdbcType="INTEGER" property="sid"/>  <result column="sname" jdbcType="VARCHAR" property="sname"/>  <result column="sex" jdbcType="VARCHAR" property="sex"/> </resultMap></mapper>

然后就是最关键的班级实体的配置文件了

Grade.

<?"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="Grade"> <resultMap type="entity.Grade" id="GradeResult">  <id column="gid" jdbcType="INTEGER" property="gid"/>  <result column="gname" jdbcType="VARCHAR" property="gname"/>  <result column="gdesc" jdbcType="VARCHAR" property="gdesc"/>  <!-- 一对多关系 -->  <collection property="stus" resultMap="Student.StudentResult"></collection> </resultMap>     <!-- 查询所有信息 -->  <select id="selectAllInfo" resultMap="GradeResult">    <!-- select sid,sname,sex,g.gid,gname,gdesc from Student s,Grade g where s.gid=g.gid -->    select sid,sname,sex,g.gid,gname,gdesc from Student s left join Grade g on s.gid=g.gid  </select></mapper>

以上就是对配置文件的解释了

接下来我们就可以进行一道测试了

/*   * 1.1 查询所有的班级和班级下的所有学生(一对多)   * */  @Test  public void selectAllStu() throws Exception{    //通过配置文件获取到数据库连接信息    Reader reader = Resources.getResourceAsReader("config/Configuration.");    //通过配置信息构建一个SessionFactory工厂    SqlSessionFactory sqlsessionfactory=new SqlSessionFactoryBuilder().build(reader);    //通过SessionFaction打开一个回话通道    SqlSession session = sqlsessionfactory.openSession();    /*SqlSession session =MybatisUtil.getSession();*/    //调用配置文件中的sql语句    List<Grade> list = session.selectList("Grade.selectAllInfo");    //遍历查询出来的结果    for (Grade grade : list) {      System.out.println("班级:"+grade.getGname());      for (Student stu : grade.getStus()) {        System.out.println("学生:"+stu.getSname());      }    }        session.close();  }  

 

执行后,查询出来的结果是

 

以上是第一种一对多关系映射的方式,下面是第二种一对多映射的方法,其他的所有步骤和上面的都是一样的只有相对应的配置文件不同,所以我就只贴小配置了

Grade.

 

<?"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="Grade"> <resultMap type="entity.Grade" id="GradeResult">  <id column="gid" jdbcType="INTEGER" property="gid"/>  <result column="gname" jdbcType="VARCHAR" property="gname"/>  <result column="gdesc" jdbcType="VARCHAR" property="gdesc"/>  <!-- 一对多关系 -->  <!-- <collection property="stus" resultMap="Student.StudentResult"></collection> -->  <collection property="stus" javaType="entity.Student">    <id property="sid" column="sid"/>    <result property="sname" column="sname"/>    <result property="sex" column="sex"/>  </collection> </resultMap>     <!-- 查询所有信息 -->  <select id="selectAllInfo" resultMap="GradeResult">    <!-- select sid,sname,sex,g.gid,gname,gdesc from Student s,Grade g where s.gid=g.gid -->    select sid,sname,sex,g.gid,gname,gdesc from Student s left join Grade g on s.gid=g.gid  </select>    <!-- 新增班级并同时新增班级下的学生 -->  <!--useGeneratedKeys=true 表明采用主键生成策略    keyProperty="gid" 表明将生成的主键添加到parameterType类中的那个属性值中去   -->  <!-- <insert id="" useGeneratedKeys="true" keyProperty="gid" parameterType="entity.Grade">      </insert> --></mapper>

 

 

接下来就可以在多的一方配置一的关联关系了

Student.

<?"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="Student"> <resultMap type="entity.Student" id="StudentResult">  <id column="sid" jdbcType="INTEGER" property="sid"/>  <result column="sname" jdbcType="VARCHAR" property="sname"/>  <result column="sex" jdbcType="VARCHAR" property="sex"/>  <!-- 多对一 -->  <!-- <association property="grade" resultMap="Grade.GradeResult"></association> -->  <association property="grade" javaType="entity.Grade">    <id property="gid" column="gid"/>    <result property="gname" column="gname"/>    <result property="gdesc" column="gdesc"/>  </association> </resultMap>   <!-- 使用别名 -->  <sql id="cloums">    s.sid,s.sname,s.sex ,g.gid,g.gname,g.gdesc  </sql>  <!-- 多对一查询学生的班级 -->  <select id="selectGradeByStu" resultMap="StudentResult">    select <include refid="cloums"/> from Student s ,Grade g where s.gid=g.gid  </select>    <!-- 简单查询所有信息 -->   <select id="selectAllStu" resultMap="StudentResult">    select sid,sname,sex,gid from Student   </select>     <!--动态拼接Sql -->   <select id="selectAllStuByWhere" parameterType="entity.Student" resultMap="StudentResult">    select sid,sname,sex,gid from Student where 1=1    <if test="sname!=null and !&quot;&quot;.equals(sname.trim())">      <!-- and sname like '%'|| #{sname}|| '%' --> <!-- 模糊查询 -->      and sname like '%${sname}%'<!-- 模糊查询 -->      <!-- and sname = #{sname} -->    </if>   </select>     <!-- 新增学生信息 -->   <insert id="InsertStuInfo" parameterType="entity.Student" >     insert into Student values(SEQ_NUM.Nextval,#{sname},#{sex},1)   </insert>     <!-- 删除学生信息 -->   <insert id="DeleteStuBySid" parameterType="int">     delete from Student where sid=#{sid}   <!--或者是   delete from Student where sid=#{_parameter} -->   </insert>     <!-- 根据SID修改学生信息 -->   <update id="UpdateStuBySid" parameterType="entity.Student" >     update Student set sname=#{sname},sex=#{sex} where sid=#{sid}   </update>     </mapper>

 

 

 

 

这样就已经完成了Mybatis框架中的简单的双向一对多的配置了,怎么样,是不是没有想象中的难呢?希望对大家有点帮助吧!