基于Mybaits映射的一点心得(分享)

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：

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服务器之家。

原文链接：http://www.cnblogs.com/zhuxiansheng/p/7794292.html