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
