學習過Hibernate框架的伙伴們很容易就能簡單的配置各種映射關系(Hibernate框架的映射關系在我的blogs中也有詳細的講解)，但是在Mybatis框架中我們又如何去實現
一對多的關系映射呢？ 其實很簡單
主配置文件：Configuration.xml
<?xml version="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.xml"/>
<mapper resource="config/Grade.xml"/>
</mappers>
</configuration>
背景：學生和班級是一個典型的一對多的關系，一個班級可以對應着多個學生，所以我們隨即創建了學生對象和班級對象
學生類：Student
package entity;
/*
* 學生類
* */
public class Student {
//學生編號
private Integer sid;
//學生名稱
private String sname;
//學生性別
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;
}
}
班級類：Grade
package entity;
import java.util.HashSet;
import java.util.Set;
/*
* 班級類
* */
public class Grade {
//班級編號
private Integer gid;
//班級名稱
private String gname;
//班級描述
private String gdesc;
//班級下的學生信息
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;
}
}
實體類准備完了的話，我們就可以開始看配置文件了，也是最關鍵的一部分
首先講簡單點的學生實體類對應的配置文件
Student.xml
<?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="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>
然后就是最關鍵的班級實體的配置文件了
Grade.xml
<?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="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"/>
<!-- 一對多關系 -->
<collection property="stus" resultMap="Student.StudentResult"></collection>
</resultMap>
<!-- 查詢所有信息 -->
<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>
以上就是對配置文件的解釋了
接下來我們就可以進行一道測試了
/*
* 1.1 查詢所有的班級和班級下的所有學生(一對多)
* */
@Test
public void selectAllStu() throws Exception{
//通過配置文件獲取到數據庫連接信息
Reader reader = Resources.getResourceAsReader("config/Configuration.xml");
//通過配置信息構建一個SessionFactory工廠
SqlSessionFactory sqlsessionfactory=new SqlSessionFactoryBuilder().build(reader);
//通過SessionFaction打開一個回話通道
SqlSession session = sqlsessionfactory.openSession();
/*SqlSession session =MybatisUtil.getSession();*/
//調用配置文件中的sql語句
List<Grade> list = session.selectList("Grade.selectAllInfo");
//遍歷查詢出來的結果
for (Grade grade : list) {
System.out.println("班級："+grade.getGname());
for (Student stu : grade.getStus()) {
System.out.println("學生："+stu.getSname());
}
}
session.close();
}
執行后，查詢出來的結果是
以上是第一種一對多關系映射的方式，下面是第二種一對多映射的方法，其他的所有步驟和上面的都是一樣的只有相對應的配置文件不同，所以我就只貼小配置了
Grade.xml
<?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="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"/>
<!-- 一對多關系 -->
<!-- <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>
<!-- 查詢所有信息 -->
<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>
<!-- 新增班級並同時新增班級下的學生 -->
<!--useGeneratedKeys=true 表明采用主鍵生成策略
keyProperty="gid" 表明將生成的主鍵添加到parameterType類中的那個屬性值中去
-->
<!-- <insert id="" useGeneratedKeys="true" keyProperty="gid" parameterType="entity.Grade">
</insert> -->
</mapper>
接下來就可以在多的一方配置一的關聯關系了
Student.xml
<?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="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"/>
<!-- 多對一 -->
<!-- <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>
<!-- 使用別名 -->
<sql id="cloums">
s.sid,s.sname,s.sex ,g.gid,g.gname,g.gdesc
</sql>
<!-- 多對一查詢學生的班級 -->
<select id="selectGradeByStu" resultMap="StudentResult">
select <include refid="cloums"/> from Student s ,Grade g where s.gid=g.gid
</select>
<!-- 簡單查詢所有信息 -->
<select id="selectAllStu" resultMap="StudentResult">
select sid,sname,sex,gid from Student
</select>
<!--動態拼接Sql -->
<select id="selectAllStuByWhere" parameterType="entity.Student" resultMap="StudentResult">
select sid,sname,sex,gid from Student where 1=1
<if test="sname!=null and !"".equals(sname.trim())">
<!-- and sname like '%'|| #{sname}|| '%' --> <!-- 模糊查詢 -->
and sname like '%${sname}%'<!-- 模糊查詢 -->
<!-- and sname = #{sname} -->
</if>
</select>
<!-- 新增學生信息 -->
<insert id="InsertStuInfo" parameterType="entity.Student" >
insert into Student values(SEQ_NUM.Nextval,#{sname},#{sex},1)
</insert>
<!-- 刪除學生信息 -->
<insert id="DeleteStuBySid" parameterType="int">
delete from Student where sid=#{sid}
<!--或者是 delete from Student where sid=#{_parameter} -->
</insert>
<!-- 根據SID修改學生信息 -->
<update id="UpdateStuBySid" parameterType="entity.Student" >
update Student set sname=#{sname},sex=#{sex} where sid=#{sid}
</update>
</mapper>
上述內容摘自http://www.cnblogs.com/liujiayun/p/5814158.html！