以前一直使用Hibernate，基本上沒(méi)用過(guò)Mybatis，工作中需要做映射關(guān)系，簡(jiǎn)單的了解下Mybatis的映射。
兩者相差不多都支持一對(duì)一，一對(duì)多，多對(duì)多，本章簡(jiǎn)單介紹一對(duì)一的使用以及注意點(diǎn)。
建表語(yǔ)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', '宏偉集團(tuán)', '1', '跨國(guó)集團(tuán)'); |
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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：子查詢(xún)
JAVA代碼：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：（如果是一堆多的話“brandObject”改成實(shí)體List屬性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：實(shí)體當(dāng)中的字段名 select：引入的另一個(gè)xxxMapper.xml的getCompanyInfo方法
這樣當(dāng)查詢(xún)用的映射時(shí)檢測(cè)到有select就會(huì)執(zhí)行你引入的另一個(gè)Mapper的查詢(xún)方法，查詢(xún)條件是company_id= 查詢(xún)方法的參數(shù)
運(yùn)行結(jié)果
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companyName = |
形式二：關(guān)聯(lián)查詢(xún)
映射配置實(shí)體測(cè)試類(lèi)一樣:
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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" /> <!-- 查詢(xún)會(huì)有賦值紊亂問(wèn)題 --> <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} --> <!-- 查詢(xún)會(huì)有賦值紊亂問(wèn)題 --> 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：實(shí)體當(dāng)中的字段名 resultMap :引入另一個(gè)Mapper的映射
值得注意的是：因?yàn)槭乔短子成洌孕问蕉趦蓚€(gè)實(shí)體字段名一樣的情況下會(huì)引發(fā)字段賦值的紊亂，例如兩個(gè)實(shí)體都有name 當(dāng)?shù)谝粋€(gè)實(shí)體name有值，第二個(gè)實(shí)體name沒(méi)有值的時(shí)候，查詢(xún)出來(lái)的結(jié)果是兩個(gè)實(shí)體name都有值，且都是一樣的為第一個(gè)實(shí)體的name值
運(yùn)行結(jié)果為
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companyName = 宏偉集團(tuán) |
顯然運(yùn)行結(jié)果不是我們想要的結(jié)果
以上簡(jiǎn)單的Demo希望能幫助初學(xué)Mybatis童鞋！！
這篇基于Mybaits映射的一點(diǎn)心得(分享)就是小編分享給大家的全部?jī)?nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持服務(wù)器之家。
原文鏈接：http://www.cnblogs.com/zhuxiansheng/p/7794292.html
