JAVAWEB（三）mybatis实现多对一等关联查询

一.在数据库中建立相应的表

use mybatis ;
-- 删除表
drop table if exists  items ;
drop table if exists  orders ;
drop table if exists  users ;

-- 创建表
create table users(id int primary key auto_increment , name           
varchar(20) , age int);
create table orders(id int primary key auto_increment ,       
orderno varchar(20) , uid int);
create table items(id int primary key auto_increment ,     
itemname varchar(20) , oid int);

-- 插入用户
insert into users(name,age) values('tom',12);
insert into users(name,age) values('tomas',13);

-- 插入订单
insert into orders(orderno,uid) values('No001',1);
insert into orders(orderno,uid) values('No002',1);
insert into orders(orderno,uid) values('No003',2);
insert into orders(orderno,uid) values('No004',2);

-- 插入订单项
insert into items(itemname,oid) values('item001',1);
insert into items(itemname,oid) values('item002',1);
insert into items(itemname,oid) values('item003',2);
insert into items(itemname,oid) values('item004',2);
insert into items(itemname,oid) values('item005',3);
insert into items(itemname,oid) values('item006',3);
insert into items(itemname,oid) values('item007',4);
insert into items(itemname,oid) values('item008',5);


select * from users ;
select * from orders ;
select * from items ;

二.建立实体类，用于去映射数据库中的表

• 建立类

  [Order.java]
   public class Order {
       private Integer id ;
       private String orderNo ;
       //简历关联关系
       private User user ;
  
       //get/set
   }
  
   [Item.java]
   public class Item {
       private Integer id;
       private String itemName;
       //订单项和订单之间的关联关系
       private Order order;
       //get/set
   }
  

• 引入映射文件

• 测试类

  @Test
        public void selectOne() throws Exception {
  String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(inputStream);
            SqlSession s = sf.openSession();
            Order order = s.selectOne("orders.selectOne",1);
            System.out.println(order.getOrderNo());
            s.commit();
            s.close();
        }
  
        @Test
        public void selectAll() throws Exception {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(inputStream);
            SqlSession s = sf.openSession();
            List list = s.selectList("orders.selectAll");
            for(Order o : list){
                System.out.println(o.getOrderNo() + " : " + o.getUser().getName());
            }
            s.commit();
            s.close();
        }
  

三.配置一对多的应用

• 1.在User中增加orders集合。

        public class User {
        ...
            private List orders ;
        //get/set
    }
  

  • 2.改造UserMapper.xml

  select
    u.id uid ,
    u.name uname ,
    u.age uage ,
    o.id oid ,
    o.orderno oorderno
  from users u
    left outer join orders o on u.id = o.uid
  where u.id = #{id}


    
    
    
    
    
        
        
    




     select
    u.id uid ,
    u.name uname ,
    u.age uage ,
    o.id oid ,
    o.orderno oorderno
  from users u
    left outer join orders o on u.id = o.uid

四.组合多对一和一对多关联关系到一个实体(Order)中

---

• 1.关系

  Order() -> (1)User
  Order(1) -> ()Item

• 2.Order.java

 class Order{
        ...
        List items ;
        //get/set   
    }
2'.修改配置文件增加别名
    [resources/mybatis-config.xml]
    
    
    
        
            
            
            
        
        
            
                
                
                    
                    
                    
                    
                
            
        
        
        
            
            
        
    

• 3.OrderMapper.xml

   
   
   
       
         insert into orders(orderno,uid) values(#{orderNo},#{user.id})
       
  
       
       
         select
           o.id      oid ,
           o.orderno oorderno ,
           o.uid     uid ,
           u.name    uname ,
           u.age     uage ,
           i.id      iid,
           i.itemname iitemname
         from orders o
           left outer join users u on o.uid = u.id
           left outer join items i on o.id = i.oid
         where o.id = #{id}
       
       
       
         select
           o.id      oid ,
           o.orderno oorderno ,
           o.uid     uid ,
           u.name    uname ,
           u.age     uage ,
           i.id      iid,
           i.itemname iitemname
         from orders o
           left outer join users u on o.uid = u.id
           left outer join items i on o.id = i.oid
       
       
       
           
           
           
               
               
               
           
           
               
               
           
       
   
  

• 4.测试

    @Test
    public void selectOne() throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession s = sf.openSession();
        Order order = s.selectOne("orders.selectOne",1);
        System.out.println(order.getOrderNo() + order.getUser().getName());
        for(Item i : order.getItems()){
            System.out.println(i.getId() + ":" + i.getItemName());
        }
        s.commit();
        s.close();
    }