Question

我正在研究一个有关创建简单Web应用程序的项目。我正在创建有关酒店的网络应用程序，但是关于房间预订的问题。我有3种房间，我想当某人预订房间时，另一个人不能在同一时期预订同一房间。问题在于这种控制。我已经编写了这段代码：

回答后更新代码

 Statement  st =  con.createStatement();
        Statement stmt = con.createStatement();
        out.println("connection successfull");
        int total = 0;
        ResultSet rs3 = stmt.executeQuery( "SELECT COUNT(*) as total FROM reservation WHERE idRoom = '" + idRoom + 
                "' AND ('" + arrivaldate + "' >= arrivaldate AND '" + arrivaldate + "' <= departuredate) OR ('" + departuredate + "' >= arrivaldate "
                + "AND '" + departuredate + "' <= departuredate)");
        rs3.next(); // You'll ever have only one row
        total = rs3.getInt("total");


       /* String query = "SELECT COUNT(*) FROM reservation WHERE idRoom = '" + idRoom + 
                "' AND ('" + arrivaldate + "' >= arrivaldate AND '" + arrivaldate + "' <= departuredate) OR ('" + departuredate + "' >= arrivaldate "
                        + "AND '" + departuredate + "' <= departuredate)" ;

        */

       // ResultSet rs2  = stmt.executeQuery(check);
        out.println("<h1> Stringa check eseguito </h1>");


        if( total  > 0) { // THIS DOESN't WORK OF COURSE    
            response.sendRedirect("home.jsp");
        }
        else {
         st.executeUpdate("insert into reservation (login,email,typeroom,idRoom,arrivaldate,departuredate)values ('"+login+"','"+email+"','"+typeroom+"','"+idRoom+"','"+arrivaldate+"','"+departuredate+"')");
        }

但是它不能正常工作，因为它让我用相同的数据预订同一房间。您认为我该怎么办？感谢您的关注。

Answer 1

首先，您完全忽略了总数：

while(rs3.next()){
   rs3.getInt("total");
}

应该是：

rs3.next(); // You'll ever have only one row
total = rs3.getInt("total");

第二，永远不要在查询中使用串联：

ResultSet rs3 = stmt.executeQuery( "SELECT COUNT(*) as total FROM reservation WHERE idRoom = '" + idRoom + 
                    "' AND ('" + arrivaldate + "' >= arrivaldate AND '" + arrivaldate + "' <= departuredate) OR ('" + departuredate + "' >= arrivaldate "
                    + "AND '" + departuredate + "' <= departuredate)");

始终使用PreparedStatements代替：

 PreparedStatement ps = stmt.prepareStatement( "SELECT COUNT(*) as total FROM reservation WHERE idRoom = ? AND (? >= arrivaldate AND ? <= departuredate) OR (? >= arrivaldate AND ? <= departuredate)");

int c = 0;
ps.setInt(++c, idRoom);
ps.setDate(++c, arrivaldate);
ps.setDate(++c, departuredate);
ps.setDate(++c, arrivaldate);
ps.setDate(++c, departuredate);

ResultSet rs = ps.executeQuery();
// And your usual code here

数据库查询和Java

1 个答案: