MyBatis是一個支持普通SQL查詢，存儲過程和高級映射的優秀持久層框架。MyBatis消除了幾乎所有的JDBC代碼和參數的手工設置以及對結果集的檢索封裝。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）映射成數據庫中的記錄。
一對一映射
在生活中，一對一的例子還是有的，比如啦，學生和身份證哦，或者在我國，實行的是一夫一妻制度哦。那么我們以學生和身份證每個學生只有一張身份證，而每張身份證的主人當然只有一個啦。
數據庫腳本：
-- 刪除數據庫drop database if exists mybaits;-- 創建數據庫create database if not exists mybatis default character set utf8;-- 選擇數據庫use mybatis;-- 刪除數據表drop table if exists student ;drop table if exists card;-- 創建數據表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));-- 增加測試數據insert into card (cid,num) values(1,'123456789012345678');insert into student (sid,sname,scid) values(1,'哈哈',1);
新建一個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"/><!-- 關聯字段不要寫 --></resultMap><select id="findById" parameterType="integer" resultMap="studentMap">select s.sid,s.sname,c.cid,c.num from student s,card cwhere s.scid = c.cid and s.sid = #{sid}</select></mapper>在src下新建一個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><!-- 設置一個默認的環境信息 --><environments default="mysql_developer"><!-- 連接MySQL環境信息 --><environment id="mysql_developer"><!-- MyBatis使用jdbc事務管理器 --><transactionManager type="jdbc"/><!-- MyBatis使用連接池方式來獲取連接對象 --><dataSource type="pooled"><!-- 配置與數據庫交互的4個必要屬性 --><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環境信息 --><environment id="oracle_developer"><!-- MyBatis使用jdbc事務管理器 --><transactionManager type="jdbc"/><!-- MyBatis使用連接池方式來獲取連接對象 --><dataSource type="pooled"><!-- 配置與數據庫交互的4個必要屬性 --><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 ;//私有化構造方法private MyBatisUtil(){}//加載位于src/Mybatis.cfg.xmlstatic{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與當前線程綁定在一起threadLocal.set(sqlSession);}}return sqlSession;}/*** 關閉SqlSession 并與當前線程分開*/public static void closeSqlSession(){//從當前線程中獲取SqlSession對象SqlSession sqlSession = threadLocal.get();//如果SqlSession對象非空if(sqlSession != null){//關閉SqlSession對象sqlSession.close();//分離當前線程與SqlSession的關系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號學生的信息與身份證信息@Testpublic void testFindById() throws Exception{StudentCardDAO dao = new StudentCardDAO();Student student = dao.findById(1);System.out.println(student.getSid()+":"+student.getSname() } }這時我們只能查詢1號學生的姓名，但是我們不能去查詢它的身份號號，因為此時的card屬性的值為null，從StudentMapper.xml中可以看出
<select id="findById" parameterType="integer" resultMap="studentMap">
MyBatis在解析這一句的時候只能將查詢的數據封裝到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的關聯屬性--><association property="card" resultMap="cardNameSpace.cardMap"/>
那么此時的StudentMapper.xml的完整內容如下：
<?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的關聯屬性--><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 cwhere s.scid = c.cid and s.sid = #{sid}</select></mapper>現在可以測試學生的身份證號碼了
將持久層類StuentCardDAO.java類的測試方法改為
//測試 查詢1號學生的信息與身份證信息@Testpublic 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”學生的信息與身份證信息的方法
/*** 查詢“哈哈”學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”學生的信息與身份證信息@Testpublic void testFindByName() throws Exception{StudentCardDAO dao = new StudentCardDAO();Student student = dao.findByName("哈哈");System.out.println(student.getSid()+":"+student.getSname()+":"+student.getCard().getNum());}當然如果你現在就測試，你會死的很慘，因為你沒有在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 cwhere 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數據庫腳本
-- 刪除數據庫drop database if exists mybaits;-- 創建數據庫create database if not exists mybatis default character set utf8;-- 選擇數據庫use mybatis;-- 刪除數據表drop table if exists student ;drop table if exists card;-- 創建數據表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));-- 增加測試數據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 ;//私有化構造方法private MyBatisUtil(){}//加載位于src/Mybatis.cfg.xmlstatic{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與當前線程綁定在一起threadLocal.set(sqlSession);}}return sqlSession;}/*** 關閉SqlSession 并與當前線程分開*/public static void closeSqlSession(){//從當前線程中獲取SqlSession對象SqlSession sqlSession = threadLocal.get();//如果SqlSession對象非空if(sqlSession != null){//關閉SqlSession對象sqlSession.close();//分離當前線程與SqlSession的關系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><!-- 設置一個默認的環境信息 --><environments default="mysql_developer"><!-- 連接MySQL環境信息 --><environment id="mysql_developer"><!-- MyBatis使用jdbc事務管理器 --><transactionManager type="jdbc"/><!-- MyBatis使用連接池方式來獲取連接對象 --><dataSource type="pooled"><!-- 配置與數據庫交互的4個必要屬性 --><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環境信息 --><environment id="oracle_developer"><!-- MyBatis使用jdbc事務管理器 --><transactionManager type="jdbc"/><!-- MyBatis使用連接池方式來獲取連接對象 --><dataSource type="pooled"><!-- 配置與數據庫交互的4個必要屬性 --><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的關聯屬性--><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 cwhere 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 cwhere 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號學生的信息與身份證信息@Testpublic 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”學生的信息與身份證信息@Testpublic 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，小編會及時回復大家的。在此也非常感謝大家對武林網網站的支持！
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