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MyBatis关系映射--一对一关系映射

本文详细介绍了MyBatis框架中实现一对一关系映射的两种方式：查询映射和结果映射。通过实例展示了每种映射的XML配置及Java代码实现，对比了两者的优缺点，帮助开发者根据需求选择合适的映射策略。

发表于 更新于
作者 贾永琪
13 分钟阅读
MyBatis关系映射--一对一关系映射

文章信息

  • 原文链接：https://jiayq.blog.csdn.net/article/details/88202406
  • 发布时间：2019-03-05 20:35:57
  • 阅读量：1
  • 分类：java同时被 3 个专栏收录, 订阅专栏, mybatis, MyBatis
  • 标签：#MyBatis关系映射–一对一映射, #查询映射和结果映射, #MyBatis映射方式对比, #MyBatis多表一对一映射, #MyBatis映射实例

摘要

文章浏览阅读1.1k次。本文详细介绍了MyBatis框架中实现一对一关系映射的两种方式：查询映射和结果映射。通过实例展示了每种映射的XML配置及Java代码实现，对比了两者的优缺点，帮助开发者根据需求选择合适的映射策略。

MyBatis关系映射–一对一关系

  • 1.关系映射
  • 2.关系映射的方式
    • 2.1查询映射
      • 2.2结果映射
      • 2.3不同方式的分析
  • 3.例子
    • 3.1创建一个MyBatis工程
      • 3.2导入jar包
      • 3.3实现Java类
      • 3.4properties
      • 3.5resource
      • 3.6mapper
  • 4.运行结果
  • 5.总结

1.关系映射

实际开发中，常常需要关联表进行查询，比如公民和身份证之间的联合查询，在公司，一个人有一个人的工位，一个人有一个人工作的计算机，一个工位可能有工作的计算机，等等。
一对一关系是最简单的关系，也是最基本的关系。

2.关系映射的方式

1.通过查询映射
2.通过结果映射

2.1查询映射

查询映射就是查第一个表时，取出第一个表时，查询第二个表，然后把第一个表和第二个表的结果共同返回去。查询映射就相当于查询2次，使用了2条select语句
查询映射的写法:

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<!-- 嵌套查询 -->
	<resultMap type="people" id="peopleWithCard">
		<id property="id" column="id"/>
		<result property="name" column="name"/>
		<result property="age" column="age"/>
		<result property="sex" column="sex"/>
		<association property="card" column="card_id" javaType="card"
	select="cardMapper.selectById"></association>
	</resultMap>
	<select id="selectOneByOne" parameterType="Long" resultMap="peopleWithCard">
		select <include refid="baseMapper.str_select_people"></include>
		from <include refid="baseMapper.str_table_people"></include>
		<where>
			<if test="_parameter != null and _parameter != ''">
				and id=#{_parameter}
			</if>
		</where>
	</select>

其中cardMapper.xml

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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="cardMapper">
	<select id="selectById" parameterType="Long" resultType="card">
		select <include refid="baseMapper.str_select_card"></include>
		from <include refid="baseMapper.str_table_card"></include>
		<where>
			<if test="_parameter != null and _parameter != ''">
				and id=#{_parameter}
			</if>
		</where>
	</select>
	<insert id="insertCard" parameterType="card">
		insert into <include refid="baseMapper.str_table_card"></include>(<include refid="baseMapper.str_select_card"></include>) values(#{id},#{code})
	</insert>
</mapper>

2.2结果映射

结果映射就是通过一条select语句查询出所有的结果，然后把返回的数据封装为实体。
结果映射的写法：

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<!-- 嵌套结果 -->
	<sql id="str_select_people_card">
		p.id,p.name,p.age,p.sex,p.card_id,c.code
	</sql>
	<sql id="str_table_people_card">
		people p,card c
	</sql>
	<resultMap type="people" id="resultPeopleWithCard">
		<id property="id" column="id"/>
		<result property="name" column="name"/>
		<result property="age" column="age"/>
		<result property="sex" column="sex"/>
		<association property="card" javaType="card">
			<id property="id" column="card_id"/>
			<result property="code" column="code"/>
		</association>
	</resultMap>
	<select id="selectResult" parameterType="Long" resultMap="resultPeopleWithCard">
		select <include refid="str_select_people_card"></include>
		from <include refid="str_table_people_card"></include>
		<where>
			c.id = p.card_id
			<if test="_parameter != null and _parameter != ''">
				and p.id=#{_parameter}
			</if>
		</where>
	</select>

2.3不同方式的分析

首先关系的映射在不同的方式中，使用不同的方法来实现映射。
在查询映射中，映射关系是通过一条新的通过id查询第二个表的SQL来完成的，如果没有通过id查询第二个表的映射，或者这个映射出现了问题，那么整体的查询映射也不会实现。也就是说查询映射依赖于外部已实现的通过id查询（或者其他主键查询，结果必须唯一）
在结果映射中，映射关系是通过SQL语句的where条件来实现的，mapper的映射只是实现结果的封装。结果映射不依赖与任何外部资源，而且结果映射只需要一条select即可实现。
优缺点：
查询映射，需要2条SQL实现；
结果映射，不需要依赖于外部资源；

查询映射，复用性较好，SQL难度较低；
结果映射，复用性差，SQL难度高。

特别是多个表进行关系的映射时，如果使用查询映射，其查询逻辑较为简单，易于修改，易于开发。
但是因为查询映射需要执行多条语句，肯定没有一次性返回结果的效率高，而且因为查询映射需要依赖多个外部资源，集成难度大，结果映射只需要专注于写SQL即可。

3.例子

3.1创建一个MyBatis工程

在这里插入图片描述

3.2导入jar包

在这里插入图片描述

3.3实现Java类

在这里插入图片描述

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package com.client;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import com.util.MyBatisSessionUtils;

public class Main {
	
	@Test
	public void queryCard(){
		SqlSession session = MyBatisSessionUtils.getSession();
		System.out.println(session.selectOne("cardMapper.selectById",1));
		session.close();
	}
	
	@Test
	public void queryPeople(){
		SqlSession session = MyBatisSessionUtils.getSession();
		System.out.println(session.selectOne("peopleMapper.selectById", 103L));
		session.close();
	}
	
	@Test
	public void queryPeopleWithCard(){
		SqlSession session = MyBatisSessionUtils.getSession();
		System.out.println(session.selectOne("oneByOneMapper.selectOneByOne",103L));
		session.close();
	}
	
	@Test
	public void queryPeopleWithCardResult(){
		SqlSession session = MyBatisSessionUtils.getSession();
		System.out.println(session.selectOne("oneByOneMapper.selectResult",103L));
		session.close();
	}
	
}




package com.domain;

import java.io.Serializable;

public class Card implements Serializable{

	/**
	 * 
	 */
	private static final long serialVersionUID = -5398573250153908121L;

	private Long id;
	
	private String code;

	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	public String getCode() {
		return code;
	}

	public void setCode(String code) {
		this.code = code;
	}

	@Override
	public String toString() {
		return "[id="+this.id+",code="+this.code+"]";
	}
	
}




package com.domain;

import java.io.Serializable;

public class People implements Serializable{

	/**
	 * 
	 */
	private static final long serialVersionUID = -3270893239281340723L;

	private Long id;
	
	private String name;
	
	private Integer age;
	
	private Integer sex;
	
	private Card card;

	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Integer getAge() {
		return age;
	}

	public void setAge(Integer age) {
		this.age = age;
	}

	public Integer getSex() {
		return sex;
	}

	public void setSex(Integer sex) {
		this.sex = sex;
	}

	public Card getCard() {
		return card;
	}

	public void setCard(Card card) {
		this.card = card;
	}

	@Override
	public String toString() {
		return "people [id=" + this.id + ",name=" + this.name + ",age="
				+ this.age + ",sex=" + this.sex + ",code=" + this.card + "]";
	}

}




package com.util;

import java.io.Reader;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class MyBatisSessionUtils {

	private static SqlSessionFactory sessionFactory = null;
	
	private static final String PATH="com/resource/mybatis.xml";
	
	static{
		try{
			Reader reader = Resources.getResourceAsReader(PATH);
			sessionFactory = new SqlSessionFactoryBuilder().build(reader);
		} catch (Exception e){
			e.printStackTrace();
		}
	}
	
	public static SqlSession getSession(){
		return sessionFactory.openSession();
	}
}

3.4properties

log4j.properties

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# Global logging configuration
log4j.rootLogger=ERROR, stdout
# MyBatis logging configuration...
log4j.logger.com=DEBUG
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

ojdbc.properties

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driver=oracle.jdbc.driver.OracleDriver
url=jdbc:oracle:thin:@127.0.0.1:1521:oracle
username=study
password=study

3.5resource

mybatis.xml

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<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
  <!-- 配置外在化 -->
  <properties resource="com/property/ojdbc.properties"></properties>
  <settings>
   	<!-- 延迟加载全局 -->
  	<setting name="lazyLoadingEnabled" value="true"/>
  	<!-- 关联对象属性的延迟加载 -->
  	<setting name="aggressiveLazyLoading" value="false"/>
  </settings>
  <!-- 改变运行时行为 -->
  <typeAliases>
	  <!-- 配置别名 -->
  	<typeAlias type="com.domain.People" alias="people"/>
  	<typeAlias type="com.domain.Card" alias="card"/>
  </typeAliases>
  <!-- 环境配置 -->
  <environments default="oracle">
    <environment id="oracle">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
  	<mapper resource="com/mapper/baseMapper.xml"/>
  	<mapper resource="com/mapper/cardMapper.xml"/>
  	<mapper resource="com/mapper/peopleMapper.xml"/>
  	<mapper resource="com/mapper/oneByOneMapper.xml"/>
  </mappers>
</configuration>

3.6mapper

baseMapper.xml

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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="baseMapper">
	<sql id="str_select_people">
		p.id,p.name,p.age,p.sex,p.card_id
	</sql>
	<sql id="str_table_people">
		people p
	</sql>
	<sql id="str_select_card">
		c.id, c.code
	</sql>
	<sql id="str_table_card">
		card c
	</sql>
</mapper>

cardMapper.xml

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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="cardMapper">
	<select id="selectById" parameterType="Long" resultType="card">
		select <include refid="baseMapper.str_select_card"></include>
		from <include refid="baseMapper.str_table_card"></include>
		<where>
			<if test="_parameter != null and _parameter != ''">
				and id=#{_parameter}
			</if>
		</where>
	</select>
	<insert id="insertCard" parameterType="card">
		insert into <include refid="baseMapper.str_table_card"></include>(<include refid="baseMapper.str_select_card"></include>) values(#{id},#{code})
	</insert>
</mapper>

peopleMapper.xml

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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="peopleMapper">
	<select id="selectById" parameterType="Long" resultType="people">
		select <include refid="baseMapper.str_select_people"></include>
		from <include refid="baseMapper.str_table_people"></include>
		<where>
			<if test="_parameter != null and _parameter != ''">
				and id=#{_parameter}
			</if>
		</where>
	</select>
	<update id="updatePeopleForCard" parameterType="people">
		update <include refid="baseMapper.str_table_people"></include>
		card_id = #{card.id}
		<where>
			<if test="card_id != null and card_id != ''">
				and id=#{id}
			</if>
		</where>
	</update>
</mapper>



<?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="oneByOneMapper">
	<!-- 嵌套查询 -->
	<resultMap type="people" id="peopleWithCard">
		<id property="id" column="id"/>
		<result property="name" column="name"/>
		<result property="age" column="age"/>
		<result property="sex" column="sex"/>
		<association property="card" column="card_id" javaType="card"
	select="cardMapper.selectById"></association>
	</resultMap>
	<select id="selectOneByOne" parameterType="Long" resultMap="peopleWithCard">
		select <include refid="baseMapper.str_select_people"></include>
		from <include refid="baseMapper.str_table_people"></include>
		<where>
			<if test="_parameter != null and _parameter != ''">
				and id=#{_parameter}
			</if>
		</where>
	</select>
	<!-- 嵌套结果 -->
	<sql id="str_select_people_card">
		p.id,p.name,p.age,p.sex,p.card_id,c.code
	</sql>
	<sql id="str_table_people_card">
		people p,card c
	</sql>
	<resultMap type="people" id="resultPeopleWithCard">
		<id property="id" column="id"/>
		<result property="name" column="name"/>
		<result property="age" column="age"/>
		<result property="sex" column="sex"/>
		<association property="card" javaType="card">
			<id property="id" column="card_id"/>
			<result property="code" column="code"/>
		</association>
	</resultMap>
	<select id="selectResult" parameterType="Long" resultMap="resultPeopleWithCard">
		select <include refid="str_select_people_card"></include>
		from <include refid="str_table_people_card"></include>
		<where>
			c.id = p.card_id
			<if test="_parameter != null and _parameter != ''">
				and p.id=#{_parameter}
			</if>
		</where>
	</select>
</mapper>

4.运行结果

queryCard

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log4j:WARN No appenders could be found for logger (org.apache.ibatis.logging.LogFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
[id=1,code=aPeopleupdateMyBatisupdateMyBatis1011]

queryPeople

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log4j:WARN No appenders could be found for logger (org.apache.ibatis.logging.LogFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
people [id=103,name=aPeopleupdate,age=53,sex=0,code=null]

queryPeopleWithCard

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log4j:WARN No appenders could be found for logger (org.apache.ibatis.logging.LogFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
people [id=103,name=aPeopleupdate,age=53,sex=0,code=[id=1,code=aPeopleupdateMyBatisupdateMyBatis1011]]

queryPeopleWithCardResult

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log4j:WARN No appenders could be found for logger (org.apache.ibatis.logging.LogFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
people [id=103,name=aPeopleupdate,age=53,sex=0,code=[id=1,code=aPeopleupdateMyBatisupdateMyBatis1011]]

5.总结

查询映射与结果映射这两种一对一关系的实现，根据需要进行选择，如果有已经实现且通过测试的查询，那么应该选择查询映射，如果没有实现的查询，且关联的表多个，那么尽可能使用结果映射。按需选择。

MyBatis关系映射--一对一映射, 查询映射和结果映射, MyBatis映射方式对比, MyBatis多表一对一映射, MyBatis映射实例
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