MyBatis一对一映射初识教程

mybatis是一个支持普通sql查询，存储过程和高级映射的优秀持久层框架。mybatis消除了几乎所有的jdbc代码和参数的手工设置以及对结果集的检索封装。mybatis可以使用简单的xml或注解用于配置和原始映射，将接口和java的pojo（plain old java objects，普通的java对象）映射成数据库中的记录。

一对一映射

在生活中，一对一的例子还是有的，比如啦，学生和身份证哦，或者在我国，实行的是一夫一妻制度哦。那么我们以学生和身份证每个学生只有一张身份证，而每张身份证的主人当然只有一个啦。

数据库脚本：

-- 删除数据库
drop database if exists mybaits;
-- 创建数据库
create database if not exists mybatis default character set utf8;
-- 选择数据库
use mybatis;
-- 删除数据表
drop table if exists student ;
drop table if exists card;
-- 创建数据表
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)
);
-- 增加测试数据
insert into card (cid,num) values(1,'123456789012345678');
insert into student (sid,sname,scid) values(1,'哈哈',1);

新建一个one2one.card.java类

package one2one;
import java.io.serializable;
/**
* 身份证
* @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类

package one2one;
import java.io.serializable;
/**
* 学生
* @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"/>
<!-- 关联字段不要写 -->
</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下新建一个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>
<!-- 设置一个默认的环境信息 -->
<environments default="mysql_developer">
<!-- 连接mysql环境信息 -->
<environment id="mysql_developer">
<!-- mybatis使用jdbc事务管理器 -->
<transactionmanager type="jdbc"/>
<!-- mybatis使用连接池方式来获取连接对象 -->
<datasource type="pooled">
<!-- 配置与数据库交互的4个必要属性 -->
<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>
<!-- 连接oracle环境信息 -->
<environment id="oracle_developer">
<!-- mybatis使用jdbc事务管理器 -->
<transactionmanager type="jdbc"/>
<!-- mybatis使用连接池方式来获取连接对象 -->
<datasource type="pooled">
<!-- 配置与数据库交互的4个必要属性 -->
<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>
<!-- 加载映射文件 -->
<mappers>
<mapper resource="one2one/cardmapper.xml"/>
<mapper resource="one2one/studentmapper.xml"/>
</mappers>
</configuration>

在util包下新建一个工具类mybatisutil.java类

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 ;
//私有化构造方法
private mybatisutil(){}
//加载位于src/mybatis.cfg.xml
static{
try {
reader reader = resources.getresourceasreader("mybatis.cfg.xml");
sqlsessionfactory=new sqlsessionfactorybuilder().build(reader);
} catch (ioexception e) {
e.printstacktrace();
}
} 
/**
* 获取sqlsession
* @return
*/
public static sqlsession getsqlsession(){
//从当前线程中获取sqlsession对象
sqlsession sqlsession = threadlocal.get();
if(sqlsession == null){
if(sqlsessionfactory != null){
sqlsession = sqlsessionfactory.opensession();
//讲sqlsession与当前线程绑定在一起
threadlocal.set(sqlsession);
}
}
return sqlsession;
}
/**
* 关闭sqlsession 并与当前线程分开
*/
public static void closesqlsession(){
//从当前线程中获取sqlsession对象
sqlsession sqlsession = threadlocal.get();
//如果sqlsession对象非空
if(sqlsession != null){
//关闭sqlsession对象
sqlsession.close();
//分离当前线程与sqlsession的关系
threadlocal.remove();
}
}
//测试
public static void main(string[] args) {
sqlsession sqlsession = mybatisutil.getsqlsession();
connection conn= sqlsession.getconnection();
system.out.println(conn != null ?"连接成功":"连接失败");
} 
}

新建持久层类stuentcarddao.java类

package one2one;
import org.apache.ibatis.session.sqlsession;
import org.junit.test;
import util.mybatisutil;
/**
* 持久层
* @author administrator
*
*/
public class studentcarddao {
/**
* 查询1号学生的信息与身份证信息
* @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();
}
}
//测试 查询1号学生的信息与身份证信息
@test
public void testfindbyid() throws exception{
studentcarddao dao = new studentcarddao();
student student = dao.findbyid(1);
system.out.println(student.getsid()+":"+student.getsname() } 
}

这时我们只能查询1号学生的姓名，但是我们不能去查询它的身份号号，因为此时的card属性的值为null，从studentmapper.xml中可以看出

<select id="findbyid" parametertype="integer" resultmap="studentmap">

mybatis在解析这一句的时候只能将查询的数据封装到sid,sname中，所以怎么办？

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的关联属性
-->
<association property="card" resultmap="cardnamespace.cardmap"/>

那么此时的studentmapper.xml的完整内容如下：

<?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的关联属性
-->
<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>

现在可以测试学生的身份证号码了

将持久层类stuentcarddao.java类的测试方法改为

//测试 查询1号学生的信息与身份证信息
@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类中增加 查询“哈哈”学生的信息与身份证信息的方法

/**
* 查询“哈哈”学生的信息与身份证信息
* @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();
}
}

并增加测试方法哦

//测试 查询“哈哈”学生的信息与身份证信息
@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());
}

当然如果你现在就测试，你会死的很惨，因为你没有在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>

这样就可以测试成功了。大功告成。

完整代码如下：

mysql数据库脚本

-- 删除数据库
drop database if exists mybaits;
-- 创建数据库
create database if not exists mybatis default character set utf8;
-- 选择数据库
use mybatis;
-- 删除数据表
drop table if exists student ;
drop table if exists card;
-- 创建数据表
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)
);
-- 增加测试数据
insert into card (cid,num) values(1,'123456789012345678');
insert into student (sid,sname,scid) values(1,'哈哈',1);

工具类mybatis.java类

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 ;
//私有化构造方法
private mybatisutil(){}
//加载位于src/mybatis.cfg.xml
static{
try {
reader reader = resources.getresourceasreader("mybatis.cfg.xml");
sqlsessionfactory=new sqlsessionfactorybuilder().build(reader);
} catch (ioexception e) {
e.printstacktrace();
}
} 
/**
* 获取sqlsession
* @return
*/
public static sqlsession getsqlsession(){
//从当前线程中获取sqlsession对象
sqlsession sqlsession = threadlocal.get();
if(sqlsession == null){
if(sqlsessionfactory != null){
sqlsession = sqlsessionfactory.opensession();
//讲sqlsession与当前线程绑定在一起
threadlocal.set(sqlsession);
}
}
return sqlsession;
}
/**
* 关闭sqlsession 并与当前线程分开
*/
public static void closesqlsession(){
//从当前线程中获取sqlsession对象
sqlsession sqlsession = threadlocal.get();
//如果sqlsession对象非空
if(sqlsession != null){
//关闭sqlsession对象
sqlsession.close();
//分离当前线程与sqlsession的关系
threadlocal.remove();
}
}
//测试
public static void main(string[] args) {
sqlsession sqlsession = mybatisutil.getsqlsession();
connection conn= sqlsession.getconnection();
system.out.println(conn != null ?"连接成功":"连接失败");
} 
}

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>
<!-- 设置一个默认的环境信息 -->
<environments default="mysql_developer">
<!-- 连接mysql环境信息 -->
<environment id="mysql_developer">
<!-- mybatis使用jdbc事务管理器 -->
<transactionmanager type="jdbc"/>
<!-- mybatis使用连接池方式来获取连接对象 -->
<datasource type="pooled">
<!-- 配置与数据库交互的4个必要属性 -->
<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>
<!-- 连接oracle环境信息 -->
<environment id="oracle_developer">
<!-- mybatis使用jdbc事务管理器 -->
<transactionmanager type="jdbc"/>
<!-- mybatis使用连接池方式来获取连接对象 -->
<datasource type="pooled">
<!-- 配置与数据库交互的4个必要属性 -->
<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>
<!-- 加载映射文件 -->
<mappers>
<mapper resource="one2one/cardmapper.xml"/>
<mapper resource="one2one/studentmapper.xml"/>
</mappers>
</configuration>

card.java和student.java

package one2one;
import java.io.serializable;
/**
* 身份证
* @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;
/**
* 学生
* @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类对应的映射文件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的关联属性
-->
<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>

持久层类studentcarddao.java类

package one2one;
import org.apache.ibatis.session.sqlsession;
import org.junit.test;
import util.mybatisutil;
/**
* 持久层
* @author administrator
*
*/
public class studentcarddao {
/**
* 查询1号学生的信息与身份证信息
* @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();
}
}
/**
* 查询“哈哈”学生的信息与身份证信息
* @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();
}
}
//测试 查询1号学生的信息与身份证信息
@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());
}
//测试 查询“哈哈”学生的信息与身份证信息
@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());
}
}

以上所述是小编给大家介绍的mybatis一对一映射初识教程，希望对大家有所帮助