Mybatis实现关联关系映射的方法示例
作者:aigo-2021 时间:2022-09-18 05:36:12
类和类有关联,将查询的结果注入到对象和对象的关联关系中
Mybatis处理的关联关系 包括一对一关联 和 一对多关联 ,例如学生关联班级是一对一 ;班级关联学生是一对多。
Mybatis实现关联关系映射,有两种方式:多表连接
和 子查询
数据库表结构
tb_project
tb_cmpany
一、实现Project关联Company一对一关联
Company.java
package com.hyxy.po;
import java.util.List;
public class Company {
private int cId;
private String cName;
public int getcId() {
return cId;
}
public void setcId(int cId) {
this.cId = cId;
}
public String getcName() {
return cName;
}
public void setcName(String cName) {
this.cName = cName;
}
}
Project.java
Project中声明Company类型的属性
package com.hyxy.po;
public class Project {
private int pId;
private String projectName;
private int cId;
private int empId;
private int amt;
private Company company;
public Company getCompany() {
return company;
}
public void setCompany(Company company) {
this.company = company;
}
public int getpId() {
return pId;
}
public void setpId(int pId) {
this.pId = pId;
}
public String getProjectName() {
return projectName;
}
public void setProjectName(String projectName) {
this.projectName = projectName;
}
public int getcId() {
return cId;
}
public void setcId(int cId) {
this.cId = cId;
}
public int getEmpId() {
return empId;
}
public void setEmpId(int empId) {
this.empId = empId;
}
public int getAmt() {
return amt;
}
public void setAmt(int amt) {
this.amt = amt;
}
}
ProjectDao.java
package com.hyxy.dao;
import com.hyxy.po.Project;
import java.util.List;
public interface ProjectDao {
public List<Project> select();
}
ProjectMapper.xml
<?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">
<!--所有映射文件中的sql语句,为了区分多个映射文件,使用命名空间+id进行区分。namespace命名空间-->
<mapper namespace="com.hyxy.dao.CompanyDao">
<!--自定义结果映射-->
<resultMap id="resultMap" type="com.hyxy.po.Company">
<!--如果数据库中有主键,写id映射-->
<id column="companyid" property="cId"></id>
<result column="companyname" property="cName"></result>
<!--一对多关系映射 (全类名.resultMap)-->
<collection property="list" resultMap="com.hyxy.dao.ProjectDao.resultMap">
</collection>
</resultMap>
<!--
查询所有的项目信息,多表连接查询关联的客户信息,
把项目信息注入到Project对象中,把客户信息注入到Company对象中
Company对象注入到Project对象的company属性中
-->
<select id="select" resultMap="resultMap">
select * from tb_company c
inner join tb_project p on p.companyid=c.companyid
</select>
</mapper>
Test1.java
package com.hyxy;
import com.hyxy.dao.ProjectDao;
import com.hyxy.po.Project;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.Reader;
import java.util.List;
//接口绑定,动态查询,关联关系查询
public class Test1 {
public static void main(String[] args) {
Reader reader=null;
try{
reader= Resources.getResourceAsReader("configuration.xml");
SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
SqlSession sqlSession=sqlSessionFactory.openSession();
//一对一
ProjectDao projectDao=sqlSession.getMapper(ProjectDao.class);
List<Project> list =projectDao.select();
for(Project p:list){
System.out.println(p.getcId()+","+p.getProjectName()+","+p.getCompany().getcName());
}
}catch (IOException e){
e.printStackTrace();
}
}
}
运行结果:
或者
ProjectMapper.xml
<!-- 使用已经定义好的一个 resultMap -->
<association property="company" resultMap="com.hyxy.dao.CompanyDao.resultMap">
</association>
CompanyMapper.xml
<mapper namespace="com.hyxy.dao.CompanyDao">
<resultMap id="resultMap" type="com.hyxy.po.Company">
<id column="companyid" property="cId"></id>
<result column="companyname" property="cname"></result>
</resultMap>
</mapper>
二、实现Company关联Project一对多关系
Company类中声明 List<Project> 属性
Company.java
package com.hyxy.po;
import java.util.List;
public class Company {
private int cId;
private String cName;
private List<Project> list;//实现Company关联Project 一对多
public List<Project> getList() {
return list;
}
public void setList(List<Project> list) {
this.list = list;
}
public int getcId() {
return cId;
}
public void setcId(int cId) {
this.cId = cId;
}
public String getcName() {
return cName;
}
public void setcName(String cName) {
this.cName = cName;
}
}
CompanyDao.java
package com.hyxy.dao;
import com.hyxy.po.Company;
import java.util.List;
public interface CompanyDao {
public List<Company> select();
}
CompanyMapper.xml
<?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">
<!--所有映射文件中的sql语句,为了区分多个映射文件,使用命名空间+id进行区分。namespace命名空间-->
<mapper namespace="com.hyxy.dao.CompanyDao">
<!--自定义结果映射-->
<resultMap id="resultMap" type="com.hyxy.po.Company">
<!--如果数据库中有主键,写id映射-->
<id column="companyid" property="cId"></id>
<result column="companyname" property="cName"></result>
<!--一对多关系映射 (全类名.resultMap)-->
<collection property="list" resultMap="com.hyxy.dao.ProjectDao.resultMap">
</collection>
</resultMap>
<select id="select" resultMap="resultMap">
select * from tb_company c
inner join tb_project p on p.companyid=c.companyid
</select>
</mapper>
Test2.java
package com.hyxy;
import com.hyxy.dao.CompanyDao;
import com.hyxy.po.Company;
import com.hyxy.po.Project;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.Reader;
import java.util.List;
//接口绑定,动态查询,关联关系查询
public class Test2 {
public static void main(String[] args) {
Reader reader=null;
try{
reader= Resources.getResourceAsReader("configuration.xml");
SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
SqlSession sqlSession=sqlSessionFactory.openSession();
//一对多
CompanyDao companyDao=sqlSession.getMapper(CompanyDao.class);
List<Company> list= companyDao.select();
for(Company c:list){
System.out.println(c.getcName());
for(Project p:c.getList()){
System.out.println(p.getProjectName());
}
System.out.println("--------------------");
}
}catch (IOException e){
e.printStackTrace();
}
}
}
运行结果:
一对一关联使用<association>,一对多关联使用<collection>
三、Mybatis子查询方式实现关联关系查询
ProjectMapper.xml
<association property="company" javaType="com.hyxy.po.Company" column="companyid" select="com.hyxy.dao.CompanyDao.selectById">
</association>
<select id="select" resultMap="resultMap">
select * from tb_project
</select>
CompanyMapper.xml
<mapper namespace="com.hyxy.dao.CompanyDao">
<resultMap id="resultMap" type="com.hyxy.po.Company">
<id column="companyid" property="companyId"></id>
<result column="companyname" property="companyName"></result>
<collection property="list" resultMap="com.hyxy.dao.ProjectDao.resultMap">
</collection>
</resultMap>
<select id="select" resultMap="resultMap">
select * from tb_company c inner join tb_project p on c.companyid = p.companyid
</select>
<select id="selectById" resultMap="resultMap" parameterType="int">
select * from tb_company where companyid = #{id}
</select>
</mapper>
来源:https://blog.csdn.net/aigo_2021/article/details/125833490
标签:Mybatis,关联关系,映射
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