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MyBatis系列：（6）一对一映射
0、准备SQL语句(mysql)
CREATE TABLE cards( cid INT(5) PRIMARY KEY, cnum VARCHAR(18) ); CREATE TABLE students( sid INT(5) PRIMARY KEY, sname VARCHAR(10), scard_id INT(5), CONSTRAINT students_fk FOREIGN KEY(scard_id) REFERENCES cards(cid) ); INSERT INTO cards(cid,cnum) VALUES(1,‘111‘); INSERT INTO students(sid,sname,scard_id) VALUES(2,‘小明‘,1); SELECT * FROM cards; SELECT * FROM students; SELECT s.sid,s.sname,c.cid,c.cnum FROM students s INNER JOIN cards c ON s.scard_id=c.cid
2、entity类
Student.java
package com.rk.entity;
public class Student {
private Integer id;
private String name;
private Card card;
public Student(){}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Card getCard() {
return card;
}
public void setCard(Card card) {
this.card = card;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + ", card=" + card + "]";
}
}Card.java
package com.rk.entity;
public class Card {
private Integer id;
private String num;
private Student student;
public Card(){}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getNum() {
return num;
}
public void setNum(String num) {
this.num = num;
}
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
@Override
public String toString() {
return "Card [id=" + id + ", num=" + num + "]";
}
}3、mybatis的映射文件
CardMapp.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="cardNamespace"> <resultMap type="com.rk.entity.Card" id="cardMap"> <id property="id" column="cid"/> <result property="num" column="cnum"/> </resultMap> </mapper>
StudentMapper.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="studentNamespace">
<resultMap type="com.rk.entity.Student" id="studentMap">
<id property="id" column="sid"/>
<result property="name" column="sname"/>
<association property="card" resultMap="cardNamespace.cardMap"></association>
</resultMap>
<select id="findById" parameterType="int" resultMap="studentMap">
select s.sid,s.sname,c.cid,c.cnum
from students s inner join cards c on s.scard_id=c.cid
and s.sid=#{id}
</select>
</mapper>4、mybatis主配置包含映射文件
mybatis.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>
<properties resource="db.properties"></properties>
<typeAliases>
<typeAlias type="com.rk.entity.Emp" alias="emp"/>
</typeAliases>
<environments default="mysql_developement">
<environment id="mysql_developement">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="http://www.mamicode.com/${mysql.driver}"/>
<property name="url" value="http://www.mamicode.com/${mysql.url}"/>
<property name="username" value="http://www.mamicode.com/${mysql.username}"/>
<property name="password" value="http://www.mamicode.com/${mysql.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/rk/entity/CardMapper.xml"/>
<mapper resource="com/rk/entity/StudentMapper.xml"/>
</mappers>
</configuration>db.properties
mysql.driver=com.mysql.jdbc.Driver mysql.url=jdbc:mysql://127.0.0.1:3306/testdb mysql.username=root mysql.password=root
5、MyBatisUtils.java
package com.rk.utils;
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 MyBatisUtils {
private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
private static SqlSessionFactory sqlSessionFactory;
static{
try {
Reader reader = Resources.getResourceAsReader("mybatis.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
private MyBatisUtils(){}
public static SqlSession getSqlSession(){
SqlSession sqlSession = threadLocal.get();
if(sqlSession == null){
sqlSession = sqlSessionFactory.openSession();
threadLocal.set(sqlSession);
}
return sqlSession;
}
public static void closeSqlSession(){
SqlSession sqlSession = threadLocal.get();
if(sqlSession != null){
sqlSession.close();
threadLocal.remove();
}
}
public static void main(String[] args) {
SqlSession sqlSession = MyBatisUtils.getSqlSession();
Connection conn = sqlSession.getConnection();
System.out.println(conn);
}
}6、StudentCardDao.java
package com.rk.dao;
import org.apache.ibatis.session.SqlSession;
import com.rk.entity.Student;
import com.rk.utils.MyBatisUtils;
public class StudentCardDao {
public Student findById(int id){
SqlSession sqlSession = null;
try{
sqlSession = MyBatisUtils.getSqlSession();
Student stu = sqlSession.selectOne("studentNamespace.findById", id);
return stu;
}
catch(Exception e){
e.printStackTrace();
sqlSession.rollback();
throw new RuntimeException(e);
}
finally{
MyBatisUtils.closeSqlSession();
}
}
public static void main(String[] args) {
StudentCardDao dao = new StudentCardDao();
Student stu = dao.findById(2);
System.out.println(stu);
}
}MyBatis系列：（6）一对一映射
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