Java对象持久化学习二

1. 一对多的对象关系 customer and order

    一个customer有多个订单

    public class Customer {
  
        private Set orders=new HashSet();

        public Customer() {}

        public Set getOrders() {
           return this.orders;
        }

        public void setOrders(Set orders) {
           this.orders = orders;
        }
    }

2. 一对一的对象关系

    一个订单只能属于一个客户

    public class Order {

       private Customer customer;

    
       public Order() {}

       public Customer getCustomer() {
           return this.customer;
       }

       public void setCustomer(Customer customer) {
          this.customer = customer;
       }

    }

3. 当持久化对象时，应该考虑与它关联的对象.

   添加一个新的客户对象
  

  public void saveCustomer(Customer customer) throws Exception {
    Connection con=null;
    PreparedStatement stmt=null;
    try {
      con=getConnection(); 

     
      con.setAutoCommit(false);

      
      if(customer.getName()==null)
        throw new BusinessException("");

      

      
      long customerId=getNextId(con,"CUSTOMERS");
      //首先向数据库添加customer对象
      stmt=con.prepareStatement("insert into CUSTOMERS(ID,NAME,AGE) values(?,?,?)");
      stmt.setLong(1,customerId);
      stmt.setString(2,customer.getName());
      stmt.setInt(3,customer.getAge());
      stmt.execute();
       

      //得到customer对象的所有订单，向数据库中添加
      Iterator iterator =customer.getOrders().iterator();
      while (iterator.hasNext() ) {
        
        Order order=(Order)iterator.next();
        if(order.getOrderNumber()==null)
          throw new BusinessException("");

       
        long orderId=getNextId(con,"ORDERS");
        
        stmt=con.prepareStatement("insert into ORDERS(ID,ORDER_NUMBER,PRICE,CUSTOMER_ID)values(?,?,?,?)");
        stmt.setLong(1,orderId);
        stmt.setString(2,order.getOrderNumber());
        stmt.setDouble(3,order.getPrice());
        stmt.setLong(4,customerId);
        stmt.execute();
      }

      
      con.commit();

    }catch(Exception e){
      e.printStackTrace();
      try{
        con.rollback();
      }catch(SQLException sqlex){
        sqlex.printStackTrace(System.out);
      }
      throw e;
    }finally{
      try{
         stmt.close();
         con.close();
       }catch(Exception e){
         e.printStackTrace();
       }
    }
  }

4. 删除customer对象时也应该考虑到这种关系

     public void deleteCustomer(Customer customer) throws Exception {
    Connection con=null;
    PreparedStatement stmt=null;
    try {
      con=getConnection(); 

      
      con.setAutoCommit(false);

      //先删除订单
      stmt=con.prepareStatement("delete from ORDERS where "
                            +"CUSTOMER_ID=?" );
      stmt.setLong(1,customer.getId().longValue());
      stmt.executeUpdate();

      //然后删除客户对象
      stmt=con.prepareStatement("delete from CUSTOMERS where "
                         +"ID=?" );
      stmt.setLong(1,customer.getId().longValue());
      stmt.executeUpdate();

      
      con.commit();

    }catch(Exception e){
      try{
        con.rollback();
      }catch(SQLException sqlex){
        sqlex.printStackTrace(System.out);
      }
      throw e;
    }finally{
      try{
         stmt.close();
         con.close();
       }catch(Exception e){
         e.printStackTrace();
       }
    }
  }