先来个一对多的案例，一个人有多条评论
person
id name
p001 小王
p002 小李
comment
-----------------------------------------------------
id content personid
3 四点半v p001
2 第三个 p002
1 哈哈去 p001
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新建类
package model;
public class Person {
private String id;
private String name;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Person(){
}
public Person(String _id,String _name){
super();
this.id=_id;
this.name=_name;
}
}
package model;
public class Comment {
int id;
String content;
String personid;
Person person;
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public String getPersonid() {
return personid;
}
public void setPersonid(String personid) {
this.personid = personid;
}
public Comment(){
}
public Comment(int _id,String _content,String _personid){
super();
this.id=_id;
this.content=_content;
this.personid=_personid;
}
}
src下新建commentMapper.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="younamespace">
<select id="selectComment" parameterType="int" resultMap="commentResult">
select
a.id as comtid,
a.content as comtContent ,
b.id as personID,
b.name as personName
from comment a
LEFT JOIN person b on a.personid=b.id
where a.id=#{id}
</select>
<resultMap type="model.Comment" id="commentResult">
<id property="id" column="comtid"/>
<result property="content" column="comtContent"/>
<association property="person" javaType="model.Person" resultMap="personResult"/>
</resultMap>
<resultMap type="model.Person" id="personResult">
<id property="id" column="personID"/>
<result property="name" column="personName"/>
</resultMap>
</mapper>
src下新建mybatis-config.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" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/test" />
<property name="username" value="root" />
<property name="password" value="1234" />
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="commentMapper.xml"/>
</mappers>
</configuration>
java代码：
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//工厂类用单例模式
SqlSession session = sqlSessionFactory.openSession();
try {
Comment p = (Comment)session.selectOne("younamespace.selectComment", 1);
System.out.print(p.getContent()+" 来自 "+p.getPerson().getName());
} finally {
session.close();
}
结果：
哈哈去 来自 小王