MyBatis一對一映射初識(shí)教程

更新時(shí)間：2016年08月23日 10:49:38 作者：Java大S

MyBatis是一個(gè)支持普通SQL查詢，存儲(chǔ)過程和高級映射的優(yōu)秀持久層框架。在我們生活中一對一的例子很多見，下面通過本文給大家?guī)砹薽ybatis一對一映射初識(shí)教程，感興趣的朋友一起看下吧

MyBatis是一個(gè)支持普通SQL查詢，存儲(chǔ)過程和高級映射的優(yōu)秀持久層框架。MyBatis消除了幾乎所有的JDBC代碼和參數(shù)的手工設(shè)置以及對結(jié)果集的檢索封裝。MyBatis可以使用簡單的XML或注解用于配置和原始映射，將接口和Java的POJO（Plain Old Java Objects，普通的Java對象）映射成數(shù)據(jù)庫中的記錄。

一對一映射

在生活中，一對一的例子還是有的，比如啦，學(xué)生和身份證哦，或者在我國，實(shí)行的是一夫一妻制度哦。那么我們以學(xué)生和身份證每個(gè)學(xué)生只有一張身份證，而每張身份證的主人當(dāng)然只有一個(gè)啦。

數(shù)據(jù)庫腳本：

-- 刪除數(shù)據(jù)庫
drop database if exists mybaits;
-- 創(chuàng)建數(shù)據(jù)庫
create database if not exists mybatis default character set utf8;
-- 選擇數(shù)據(jù)庫
use mybatis;
-- 刪除數(shù)據(jù)表
drop table if exists student ;
drop table if exists card;
-- 創(chuàng)建數(shù)據(jù)表
create table card(
cid int(255),
num varchar(18),
constraint pk_cid primary key (cid)
);
create table student(
sid int(255),
sname varchar(32),
scid int(255),
constraint pk_sid primary key (sid),
constraint fk_scid foreign key (scid) references card(cid)
);
-- 增加測試數(shù)據(jù)
insert into card (cid,num) values(1,'123456789012345678');
insert into student (sid,sname,scid) values(1,'哈哈',1);

新建一個(gè)one2one.Card.java類

package one2one;
import java.io.Serializable;
/**
* 身份證
* @author Administrator
*
*/
@SuppressWarnings("serial")
public class Card implements Serializable{
private Integer cid;
private String num;
public Integer getCid() {
return cid;
}
public void setCid(Integer cid) {
this.cid = cid;
}
public String getNum() {
return num;
}
public void setNum(String num) {
this.num = num;
}
}

新建one2one.Student.java類

package one2one;
import java.io.Serializable;
/**
* 學(xué)生
* @author Administrator
*
*/
@SuppressWarnings("serial")
public class Student implements Serializable{
private Integer sid;
private String sname;
private Card card;
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 Card getCard() {
return card;
}
public void setCard(Card card) {
this.card = card;
}
}

在one2one包下新建CardMapper.xml文件

<?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="cardNameSpace">
<resultMap type="one2one.Card" id="cardMap">
<id column="cid" property="cid"/>
<result column="num" property="num"/>
</resultMap>
</mapper>

同理，在one2one包下新建StudentMapper.xml文件

<?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="studentNameSpace">
<resultMap type="one2one.Student" id="studentMap">
<id column="sid" property="sid"/>
<result column="sname" property="sname"/>
<!-- 關(guān)聯(lián)字段不要寫 -->
</resultMap>
<select id="findById" parameterType="integer" resultMap="studentMap">
select s.sid,s.sname,c.cid,c.num 
from student s,card c
where s.scid = c.cid and s.sid = #{sid}
</select>
</mapper>

在src下新建一個(gè)mybatis.cfg.xml文件，并包含StudentMapper.xml和CardMapper.xml文件

<?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>
<!-- 設(shè)置一個(gè)默認(rèn)的環(huán)境信息 -->
<environments default="mysql_developer">
<!-- 連接MySQL環(huán)境信息 -->
<environment id="mysql_developer">
<!-- MyBatis使用jdbc事務(wù)管理器 -->
<transactionManager type="jdbc"/>
<!-- MyBatis使用連接池方式來獲取連接對象 -->
<dataSource type="pooled">
<!-- 配置與數(shù)據(jù)庫交互的4個(gè)必要屬性 -->
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis"/>
<property name="username" value="root"/>
<property name="password" value="mysqladmin"/>
</dataSource>
</environment>
<!-- 連接Oracle環(huán)境信息 -->
<environment id="oracle_developer">
<!-- MyBatis使用jdbc事務(wù)管理器 -->
<transactionManager type="jdbc"/>
<!-- MyBatis使用連接池方式來獲取連接對象 -->
<dataSource type="pooled">
<!-- 配置與數(shù)據(jù)庫交互的4個(gè)必要屬性 -->
<property name="driver" value="oracle.jdbc.driver.OracleDriver"/>
<property name="url" value="jdbc:oracle:thin:@127.0.0.1:1521:orcl"/>
<property name="username" value="scott"/>
<property name="password" value="tiger"/>
</dataSource>
</environment>
</environments>
<!-- 加載映射文件 -->
<mappers>
<mapper resource="one2one/CardMapper.xml"/>
<mapper resource="one2one/StudentMapper.xml"/>
</mappers>
</configuration>

在util包下新建一個(gè)工具類MyBatisUtil.java類

package util;
import java.io.IOException;
import java.io.Reader;
import java.sql.Connection;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class MyBatisUtil {
private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
public static SqlSessionFactory sqlSessionFactory ;
//私有化構(gòu)造方法
private MyBatisUtil(){}
//加載位于src/Mybatis.cfg.xml
static{
try {
Reader reader = Resources.getResourceAsReader("mybatis.cfg.xml");
sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
e.printStackTrace();
}
} 
/**
* 獲取SQLSession
* @return
*/
public static SqlSession getSqlSession(){
//從當(dāng)前線程中獲取SqlSession對象
SqlSession sqlSession = threadLocal.get();
if(sqlSession == null){
if(sqlSessionFactory != null){
sqlSession = sqlSessionFactory.openSession();
//講sqlSession與當(dāng)前線程綁定在一起
threadLocal.set(sqlSession);
}
}
return sqlSession;
}
/**
* 關(guān)閉SqlSession 并與當(dāng)前線程分開
*/
public static void closeSqlSession(){
//從當(dāng)前線程中獲取SqlSession對象
SqlSession sqlSession = threadLocal.get();
//如果SqlSession對象非空
if(sqlSession != null){
//關(guān)閉SqlSession對象
sqlSession.close();
//分離當(dāng)前線程與SqlSession的關(guān)系
threadLocal.remove();
}
}
//測試
public static void main(String[] args) {
SqlSession sqlSession = MyBatisUtil.getSqlSession();
Connection conn= sqlSession.getConnection();
System.out.println(conn != null ?"連接成功":"連接失敗");
} 
}

新建持久層類StuentCardDAO.java類

package one2one;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import util.MyBatisUtil;
/**
* 持久層
* @author Administrator
*
*/
public class StudentCardDAO {
/**
* 查詢1號學(xué)生的信息與身份證信息
* @param id
* @return
* @throws Exception
*/
public Student findById(Integer id) throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MyBatisUtil.getSqlSession();
return sqlSession.selectOne("studentNameSpace.findById", id);
} catch (Exception e) {
e.printStackTrace();
throw e;
}finally{
MyBatisUtil.closeSqlSession();
}
}
//測試 查詢1號學(xué)生的信息與身份證信息
@Test
public void testFindById() throws Exception{
StudentCardDAO dao = new StudentCardDAO();
Student student = dao.findById(1);
System.out.println(student.getSid()+":"+student.getSname() } 
}

這時(shí)我們只能查詢1號學(xué)生的姓名，但是我們不能去查詢它的身份號號，因?yàn)榇藭r(shí)的card屬性的值為null，從StudentMapper.xml中可以看出

<select id="findById" parameterType="integer" resultMap="studentMap">

MyBatis在解析這一句的時(shí)候只能將查詢的數(shù)據(jù)封裝到sid,sname中，所以怎么辦？

在StudentMapper.xml中的

<resultMap type="one2one.Card" id="cardMap">
<id column="cid" property="cid"/>
<result column="num" property="num"/>
</resultMap>

增加

<!-- 
引入CardMapper.xml文件中的映射信息
property表示Student的關(guān)聯(lián)屬性
-->
<association property="card" resultMap="cardNameSpace.cardMap"/>

那么此時(shí)的StudentMapper.xml的完整內(nèi)容如下：

<?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="studentNameSpace">
<resultMap type="one2one.Student" id="studentMap">
<id column="sid" property="sid"/>
<result column="sname" property="sname"/>
<!-- 
引入CardMapper.xml文件中的映射信息
property表示Student的關(guān)聯(lián)屬性
-->
<association property="card" resultMap="cardNameSpace.cardMap"/>
</resultMap>
<select id="findById" parameterType="integer" resultMap="studentMap">
select s.sid,s.sname,c.cid,c.num 
from student s,card c
where s.scid = c.cid and s.sid = #{sid}
</select>
</mapper>

現(xiàn)在可以測試學(xué)生的身份證號碼了

將持久層類StuentCardDAO.java類的測試方法改為

//測試 查詢1號學(xué)生的信息與身份證信息
@Test
public void testFindById() throws Exception{
StudentCardDAO dao = new StudentCardDAO();
Student student = dao.findById(1);
System.out.println(student.getSid()+":"+student.getSname()+":"+student.getCard().getNum());
}

同理

在StudentDAO.java類中增加查詢“哈哈”學(xué)生的信息與身份證信息的方法

/**
* 查詢“哈哈”學(xué)生的信息與身份證信息
* @param name
* @return
* @throws Exception
*/
public Student findByName(String name) throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MyBatisUtil.getSqlSession();
return sqlSession.selectOne("studentNameSpace.findByName", name);
} catch (Exception e) {
e.printStackTrace();
throw e;
}finally{
MyBatisUtil.closeSqlSession();
}
}

并增加測試方法哦

//測試 查詢“哈哈”學(xué)生的信息與身份證信息
@Test
public void testFindByName() throws Exception{
StudentCardDAO dao = new StudentCardDAO();
Student student = dao.findByName("哈哈");
System.out.println(student.getSid()+":"+student.getSname()+":"+student.getCard().getNum());
}

當(dāng)然如果你現(xiàn)在就測試，你會(huì)死的很慘，因?yàn)槟銢]有在StudentMapper.xml文件中配置<select>哦，所以在StudentMapper.xml文件中增加<select>配置信息

<select id="findByName" parameterType="string" resultMap="studentMap">
select s.sid,s.sname,c.cid,c.num 
from student s,card c
where s.scid = c.cid and s.sname = #{sname}
</select>

這樣就可以測試成功了。大功告成。

完整代碼如下：

MySQL數(shù)據(jù)庫腳本

-- 刪除數(shù)據(jù)庫
drop database if exists mybaits;
-- 創(chuàng)建數(shù)據(jù)庫
create database if not exists mybatis default character set utf8;
-- 選擇數(shù)據(jù)庫
use mybatis;
-- 刪除數(shù)據(jù)表
drop table if exists student ;
drop table if exists card;
-- 創(chuàng)建數(shù)據(jù)表
create table card(
cid int(255),
num varchar(18),
constraint pk_cid primary key (cid)
);
create table student(
sid int(255),
sname varchar(32),
scid int(255),
constraint pk_sid primary key (sid),
constraint fk_scid foreign key (scid) references card(cid)
);
-- 增加測試數(shù)據(jù)
insert into card (cid,num) values(1,'123456789012345678');
insert into student (sid,sname,scid) values(1,'哈哈',1);

工具類MyBatis.java類

package util;
import java.io.IOException;
import java.io.Reader;
import java.sql.Connection;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class MyBatisUtil {
private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
public static SqlSessionFactory sqlSessionFactory ;
//私有化構(gòu)造方法
private MyBatisUtil(){}
//加載位于src/Mybatis.cfg.xml
static{
try {
Reader reader = Resources.getResourceAsReader("mybatis.cfg.xml");
sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
e.printStackTrace();
}
} 
/**
* 獲取SQLSession
* @return
*/
public static SqlSession getSqlSession(){
//從當(dāng)前線程中獲取SqlSession對象
SqlSession sqlSession = threadLocal.get();
if(sqlSession == null){
if(sqlSessionFactory != null){
sqlSession = sqlSessionFactory.openSession();
//講sqlSession與當(dāng)前線程綁定在一起
threadLocal.set(sqlSession);
}
}
return sqlSession;
}
/**
* 關(guān)閉SqlSession 并與當(dāng)前線程分開
*/
public static void closeSqlSession(){
//從當(dāng)前線程中獲取SqlSession對象
SqlSession sqlSession = threadLocal.get();
//如果SqlSession對象非空
if(sqlSession != null){
//關(guān)閉SqlSession對象
sqlSession.close();
//分離當(dāng)前線程與SqlSession的關(guān)系
threadLocal.remove();
}
}
//測試
public static void main(String[] args) {
SqlSession sqlSession = MyBatisUtil.getSqlSession();
Connection conn= sqlSession.getConnection();
System.out.println(conn != null ?"連接成功":"連接失敗");
} 
}

mybatis.cfg.xml文件

<?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>
<!-- 設(shè)置一個(gè)默認(rèn)的環(huán)境信息 -->
<environments default="mysql_developer">
<!-- 連接MySQL環(huán)境信息 -->
<environment id="mysql_developer">
<!-- MyBatis使用jdbc事務(wù)管理器 -->
<transactionManager type="jdbc"/>
<!-- MyBatis使用連接池方式來獲取連接對象 -->
<dataSource type="pooled">
<!-- 配置與數(shù)據(jù)庫交互的4個(gè)必要屬性 -->
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis"/>
<property name="username" value="root"/>
<property name="password" value="mysqladmin"/>
</dataSource>
</environment>
<!-- 連接Oracle環(huán)境信息 -->
<environment id="oracle_developer">
<!-- MyBatis使用jdbc事務(wù)管理器 -->
<transactionManager type="jdbc"/>
<!-- MyBatis使用連接池方式來獲取連接對象 -->
<dataSource type="pooled">
<!-- 配置與數(shù)據(jù)庫交互的4個(gè)必要屬性 -->
<property name="driver" value="oracle.jdbc.driver.OracleDriver"/>
<property name="url" value="jdbc:oracle:thin:@127.0.0.1:1521:orcl"/>
<property name="username" value="scott"/>
<property name="password" value="tiger"/>
</dataSource>
</environment>
</environments>
<!-- 加載映射文件 -->
<mappers>
<mapper resource="one2one/CardMapper.xml"/>
<mapper resource="one2one/StudentMapper.xml"/>
</mappers>
</configuration>

Card.java和Student.java

package one2one;
import java.io.Serializable;
/**
* 身份證
* @author Administrator
*
*/
@SuppressWarnings("serial")
public class Card implements Serializable{
private Integer cid;
private String num;
public Integer getCid() {
return cid;
}
public void setCid(Integer cid) {
this.cid = cid;
}
public String getNum() {
return num;
}
public void setNum(String num) {
this.num = num;
}
}
package one2one;
import java.io.Serializable;
/**
* 學(xué)生
* @author Administrator
*
*/
@SuppressWarnings("serial")
public class Student implements Serializable{
private Integer sid;
private String sname;
private Card card;
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 Card getCard() {
return card;
}
public void setCard(Card card) {
this.card = card;
}
}

Card.java的映射文件CardMapper.xml文件

<?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="cardNameSpace">
<resultMap type="one2one.Card" id="cardMap">
<id column="cid" property="cid"/>
<result column="num" property="num"/>
</resultMap>
</mapper>

Student.java類對應(yīng)的映射文件StudentMapper.xml文件

<?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="studentNameSpace">
<resultMap type="one2one.Student" id="studentMap">
<id column="sid" property="sid"/>
<result column="sname" property="sname"/>
<!-- 
引入CardMapper.xml文件中的映射信息
property表示Student的關(guān)聯(lián)屬性
-->
<association property="card" resultMap="cardNameSpace.cardMap"/>
</resultMap>
<select id="findById" parameterType="integer" resultMap="studentMap">
select s.sid,s.sname,c.cid,c.num 
from student s,card c
where s.scid = c.cid and s.sid = #{sid}
</select>
<select id="findByName" parameterType="string" resultMap="studentMap">
select s.sid,s.sname,c.cid,c.num 
from student s,card c
where s.scid = c.cid and s.sname = #{sname}
</select>
</mapper>

持久層類StudentCardDAO.java類

package one2one;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import util.MyBatisUtil;
/**
* 持久層
* @author Administrator
*
*/
public class StudentCardDAO {
/**
* 查詢1號學(xué)生的信息與身份證信息
* @param id
* @return
* @throws Exception
*/
public Student findById(Integer id) throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MyBatisUtil.getSqlSession();
return sqlSession.selectOne("studentNameSpace.findById", id);
} catch (Exception e) {
e.printStackTrace();
throw e;
}finally{
MyBatisUtil.closeSqlSession();
}
}
/**
* 查詢“哈哈”學(xué)生的信息與身份證信息
* @param name
* @return
* @throws Exception
*/
public Student findByName(String name) throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MyBatisUtil.getSqlSession();
return sqlSession.selectOne("studentNameSpace.findByName", name);
} catch (Exception e) {
e.printStackTrace();
throw e;
}finally{
MyBatisUtil.closeSqlSession();
}
}
//測試 查詢1號學(xué)生的信息與身份證信息
@Test
public void testFindById() throws Exception{
StudentCardDAO dao = new StudentCardDAO();
Student student = dao.findById(1);
System.out.println(student.getSid()+":"+student.getSname()+":"+student.getCard().getNum());
}
//測試 查詢“哈哈”學(xué)生的信息與身份證信息
@Test
public void testFindByName() throws Exception{
StudentCardDAO dao = new StudentCardDAO();
Student student = dao.findByName("哈哈");
System.out.println(student.getSid()+":"+student.getSname()+":"+student.getCard().getNum());
}
}

以上所述是小編給大家介紹的MyBatis一對一映射初識(shí)教程，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會(huì)及時(shí)回復(fù)大家的。在此也非常感謝大家對腳本之家網(wǎng)站的支持！

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