以前一直使用hibernate，基本上没用过mybatis，工作中需要做映射关系，简单的了解下mybatis的映射。
两者相差不多都支持一对一，一对多，多对多，本章简单介绍一对一的使用以及注意点。
建表语句：
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create table `bloc` (
`id` int(11) not null auto_increment,
`name` varchar(255) collate utf8_bin default null,
`company_id` int(11) default null,
`intro` varchar(255) collate utf8_bin default null,
primary key (`id`)
) engine=innodb auto_increment=2 default charset=utf8 collate=utf8_bin;
insert into`bloc` (`id`, `name`, `company_id`, `intro`) values ('1', '宏伟集团', '1', '跨国集团');
create table `company` (
`id` int(11) not null,
`name` varchar(255) collate utf8_bin default null,
`intro` varchar(255) collate utf8_bin default null,
primary key (`id`)
) engine=innodb default charset=utf8 collate=utf8_bin;
insert into company (`id`, `name`, `intro`) values ('1', '', null);
形式一：子查询
java代码：sqlsessionhelper.java
package com.demo.mybatis;
import java.io.ioexception;
import java.io.reader;
import org.apache.ibatis.io.resources;
import org.apache.ibatis.session.sqlsessionfactory;
import org.apache.ibatis.session.sqlsessionfactorybuilder;
public class sqlsessionhelper {
public static sqlsessionfactory getsessionfactory() throws ioexception{
sqlsessionfactory sessionfactory = null;
reader reader = resources.getresourceasreader("configuration.xml");
try{
sessionfactory = new sqlsessionfactorybuilder().build(reader);;
}catch(exception ex){
ex.printstacktrace();
}
return sessionfactory;
}
}
test.java:
package com.demo.mybatis;
import java.util.list;
import org.apache.ibatis.session.sqlsession;
import mapper.blocmapper;
import model.bloc;
public class test {
/**
* @param args
*/
public static void main(string[] args) {
try{
sqlsession sqlsession = sqlsessionhelper.getsessionfactory().opensession();
blocmapper blocmapper = sqlsession.getmapper(blocmapper.class);
list<bloc> blocs = blocmapper.getbloclist("1");
for (bloc bloc : blocs) {
system.out.println("companyname = "bloc.getcompany().getname());
}
}catch(exception ex){
system.out.println(ex.getmessage());
}
}
}
mapper:
package mapper;
import java.util.list;
import model.bloc;
public interface blocmapper {
public list<bloc> getbloclist(string name);
}
package mapper;
public interface companymapper {
}
model:
package model;
public class bloc {
private integer id;
private string name;
private string intro;
private company company;
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 string getintro() {
return intro;
}
public void setintro(string intro) {
this.intro = intro;
}
public company getcompany() {
return company;
}
public void setcompany(company company) {
this.company = company;
}
}
package model;
public class company {
private integer id;
private string name;
private integer intro;
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 integer getintro() {
return intro;
}
public void setintro(integer intro) {
this.intro = intro;
}
}
映射配置如下：（如果是一堆多的话“brandobject”改成实体list属性association 改成collection ）
<?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="mapper.companymapper">
<resultmap id="baseresultmap" type="model.company" >
<id column="id" property="id" jdbctype="integer" />
<result column="name" property="name" jdbctype="varchar" />
<result column="intro" property="intro" jdbctype="varchar" />
</resultmap>
<select id = "getcompanyinfo" parametertype="integer" resultmap="baseresultmap">
select * from company where id = #{id}
</select>
</mapper>
<mapper namespace="mapper.blocmapper">
<resultmap id="baseresultmap" type="model.bloc" >
<id column="id" property="id" jdbctype="integer" />
<result column="name" property="name" jdbctype="varchar" />
<result column="intro" property="intro" jdbctype="varchar" />
<association column="company_id" property="company" select="mapper.companymapper.getcompanyinfo">
</association>
</resultmap>
<select id="getbloclist" parametertype="string" resultmap="baseresultmap">
select * from bloc where name = #{name}
</select>
</mapper>
column：表中的字段 property：实体当中的字段名 select：引入的另一个xxxmapper.xml的getcompanyinfo方法
这样当查询用的映射时检测到有select就会执行你引入的另一个mapper的查询方法，查询条件是company_id= 查询方法的参数
运行结果
companyname =
形式二：关联查询
映射配置实体测试类一样:
<?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="mapper.blocmapper">
<resultmap id="baseresultmap" type="model.bloc" >
<id column="id" property="id" jdbctype="integer" />
<result column="name" property="name" jdbctype="varchar" />
<result column="intro" property="intro" jdbctype="varchar" />
<!-- 查询会有赋值紊乱问题 -->
<association column="company_id" property="company" resultmap = "mapper.companymapper.baseresultmap">
</association>
<!-- <association column="company_id" property="company" select="mapper.companymapper.getcompanyinfo">
</association> -->
</resultmap>
<select id="getbloclist" parametertype="string" resultmap="baseresultmap">
<!-- select * from bloc where name = #{name} -->
<!-- 查询会有赋值紊乱问题 -->
select * from bloc b left join company c on b.company_id = c.id where b.name = #{name}
</select>
</mapper>
column：表中的字段 property：实体当中的字段名 resultmap :引入另一个mapper的映射
值得注意的是：因为是嵌套映射，所以形式二在两个实体字段名一样的情况下会引发字段赋值的紊乱，例如两个实体都有name 当第一个实体name有值，第二个实体name没有值的时候，查询出来的结果是两个实体name都有值，且都是一样的为第一个实体的name值
运行结果为
companyname = 宏伟集团
显然运行结果不是我们想要的结果
以上简单的demo希望能帮助初学mybatis童鞋！！
这篇基于mybaits映射的一点心得(分享)就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持移动技术网。
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