基于Mybaits映射的一点心得(分享)

时间:2022-09-09 22:22:20

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');
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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

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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:

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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:

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package mapper;
 
import java.util.List;
 
import model.Bloc;
 
public interface BlocMapper {
 
 public List<Bloc> getBlocList(String name);
}
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package mapper;
 
public interface CompanyMapper {
 
}

model:

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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;
 }
  
  
}
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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 )

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<?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>
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<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

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companyName =

形式二:关联查询

映射配置实体测试类一样:

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<?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

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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