Mybatis实现关联关系映射的方法示例

目录

• 数据库表结构
•  一、实现Project关联Company一对一关联
• 二、实现Company关联Project一对多关系
•  三、Mybatis子查询方式实现关联关系查询

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 select();
}

ProjectMapper.xml

    
    
        
        
        
        
        
        
 
    
    
    
        select * from tb_company c
        inner join tb_project p on p.companyid=c.companyid
 
    
 

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 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

CompanyMapper.xml

二、实现Company关联Project一对多关系

Company类中声明 List 属性

Company.java

package com.hyxy.po;
 
import java.util.List;
 
public class Company {
    private int cId;
    private String cName;
    private List list;//实现Company关联Project 一对多
 
    public List getList() {
        return list;
    }
 
    public void setList(List 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 select();
}

CompanyMapper.xml

    
    
        
        
        
        
        
        
 
    
    
        select * from tb_company c
        inner join tb_project p on p.companyid=c.companyid
 
    
 

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 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，一对多关联使用

 三、Mybatis子查询方式实现关联关系查询

ProjectMapper.xml

    select * from tb_project

CompanyMapper.xml

    
        
        
        
    
    
    
        select * from tb_company c inner join tb_project p on c.companyid = p.companyid
    
    
        select * from tb_company where companyid = #{id}
    

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