基于Mybatis映射的一點心得(分享)

更新時間：2021年04月01日 15:20:31 作者：紅尾巴的豬

下面小編就為大家?guī)硪黄贛ybatis映射的一點心得(分享)。小編覺得挺不錯的，現(xiàn)在就分享給大家，也給大家做個參考。一起跟隨小編過來看看吧

以前一直使用Hibernate，基本上沒用過Mybatis，工作中需要做映射關(guān)系，簡單的了解下Mybatis的映射。

兩者相差不多都支持一對一，一對多，多對多，本章簡單介紹一對一的使用以及注意點。

建表語句：

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', '宏偉集團', '1', '跨國集團');

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

JAVA代碼：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：（如果是一堆多的話“brandObject”改成實體List屬性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：實體當(dāng)中的字段名 select：引入的另一個xxxMapper.xml的getCompanyInfo方法

這樣當(dāng)查詢用的映射時檢測到有select就會執(zhí)行你引入的另一個Mapper的查詢方法，查詢條件是company_id= 查詢方法的參數(shù)

運行結(jié)果

companyName =

形式二：關(guān)聯(lián)查詢

映射配置實體測試類一樣:

<?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" /> 
 <!-- 查詢會有賦值紊亂問題 --> 
 <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} --> 
 <!-- 查詢會有賦值紊亂問題 --> 
 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：實體當(dāng)中的字段名 resultMap :引入另一個Mapper的映射

值得注意的是：因為是嵌套映射，所以形式二在兩個實體字段名一樣的情況下會引發(fā)字段賦值的紊亂，例如兩個實體都有name 當(dāng)?shù)谝粋€實體name有值，第二個實體name沒有值的時候，查詢出來的結(jié)果是兩個實體name都有值，且都是一樣的為第一個實體的name值

運行結(jié)果為