mybtis关系映射及多表查询

实体关系问题

• 1:1

多表查询

package com.zakl.pojo;

import java.io.Serializable;
//返回的查询类
public class Userwithdetailpojo extends User2pojo implements Serializable {

    private  Userdetailpojo userdetailpojo;
  //省略get set toString
}

 
        
        
        
        
        
      
        
      
        
            
            
            
            
            
            
        

    

    
        select t1.userid as uid, t1.phone, t1.password ,t1.creatdate, t1.status, t2.udid , t2.address, t2.cid
        from user2 as t1 ,userdetail as t2
        
            t1.userid=t2.userid and t1.userid =#{id};
        
 
 
使用泛型方法进行测试
 
 
    public static void  queryautocommit(String methodname,Object[] objs) throws InvocationTargetException, IllegalAccessException {
        SqlSession sqlSession = MybatisUtil.getSession();
        User2Mapper user2Mapper = sqlSession.getMapper(User2Mapper.class);
        Method[] methods=user2Mapper.getClass().getMethods();
        Method method=null;
        for (int i=0;i userwithdetailpojos= (List) method.invoke(user2Mapper,objs);
        System.out.println(userwithdetailpojos);
        sqlSession.close();
    }

    @Test
    public void testdemo() throws InvocationTargetException, IllegalAccessException {
        Object[] objects=new Object[]{1};
        queryautocommit("querybyid",objects);
    }
 
 
使用分步查詢
 
 
  
        
        
        
        
        
    
  
      
        
    


        select userid , phone,password ,creatdate, status
        from user2
        
            userid =#{id};
        
    

UserdetailMapper查詢文件

    
        select * from userdetail where userid=#{userid}
    

public interface User2Mapper {
    List querybyid(@Param("id") Integer id);
    List querybystepid(@Param("id") Integer id);
}
public interface UserdetailMapper {
    List querybyUseridbystep(@Param("userid") Integer userid);
}


 @Test
    public void demo11() {
        SqlSession sqlSession = MybatisUtil.getSession();
        User2Mapper user2Mapper=sqlSession.getMapper(User2Mapper.class);
        List userwithdetailpojos = user2Mapper.querybystepid(1);
        System.out.println(userwithdetailpojos);
        sqlSession.commit();
        sqlSession.close();
    }

注意每次新增Mapper.xml時都應該在mybatis.cfg.xml中進行配置

• 1:n

多表联合查询

​ 三表结构

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​ 三个pojo类

public class UserwithBlog extends User2pojo implements Serializable {
    private List blogs;
}

public class Blog {
    private Integer id;
    private User2pojo user2pojo;
    private String title;
    private String content;
    private List comments;
}

public class Comment {
    private Integer id;
    private String comment;
    private Blog blog;
}

//接口方法
@interface
  UserwithBlog querblogbyid(@Param("userid")Integer userid);

mapper.xml配置

  
        
            
            
            
          
            
                
                
               
            
        
    


    
           select t1.userid as aid ,t1.phone ,t1.password,t1.creatdate,t1.status,
                  t2.id as bid,t2.userid,t2.title,t2.content,
                  t3.id as cid, t3.comment,t3.blogid
            from user2 as t1 ,blog as t2,comment as t3
            
                t1.userid=t2.userid and
                 t2.id=t3.blogid and
                  t1.userid=#{userid}