我在进行计算时无法保留该值

问题描述

我的ReservationID就像这个R00001但是当自动生成ReservationID时，值0不能保留在变量中。如何解决？

My ReservationID like this R00001 but when auto generate the ReservationID, the value 0 cannot keep in the variable. How to solve it ?

public void GenerateReservationID()
  {
      string sql = "SELECT * FROM Reservation";
      string cs = @"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Database.mdf;Integrated Security=True;User Instance=True";
      string s = "";

      SqlConnection con = new SqlConnection(cs);
      SqlCommand cmd = new SqlCommand(sql, con);

      con.Open();
      SqlDataReader dr = cmd.ExecuteReader();
      while (dr.Read())
      {
          s = Convert.ToString(dr["ReservationID"]);
      }
      string sub1 = s.Substring(0,1);
      string sub2 = Convert.ToString(Convert.ToInt16(s.Substring(1)) + 1);
      dr.Close();
      con.Close();

      lblRservationID.Text = sub1 + sub2;
  }

[edit]已添加代码块 - OriginalGriff [/ edit]

[edit]Code block added - OriginalGriff[/edit]

推荐答案

SELECT MAX(ReservationID) FROM Reservation 

将仅返回当前最高的数字，这是我怀疑你的感兴趣。



2）当你将一个字符串转换为一个整数时，你不会丢失零 - 但是将一个整数转换回来的常规方法字符串不会插入前导零 - 这就是你得到的效果。对于一个整数，00000001与1相同，因为前导零完全不相关。

尝试使用ToString格式来指定前导零，或者String.Format：

Will return only the current highest number, which is what I suspect you are interested in.

2) When you convert a string to an integer, you don't "lose" zeros - but the normal method to convert an integer back to a string does not insert leading zeros - so that is the effect you get. To an integer, 00000001 is the same as 1 because leading zeros are completely irrelevant.
Try using ToString with a format to specify the leading zeros instead, or String.Format:

string sub1 = s.Substring(0,1);
int reserveNp = Convert.ToInt32(s.Substring(1)) + 1;
lblReservationID.Text = string.Format("{0}{1:00000}", sub1, reserveNo);

3）虽然还有另一个问题：由于你使用SQL，很有可能在多用户环境中使用它，你在这里使用的想法是行不通的：如果两个用户同时去预订号码，那就有一个，很有可能他们都会得到相同的价值。

你在哪里创建这个预订ID，为什么不从那里保留价值？

3) There is another problem though: Since you are using SQL there is a good chance that this will be used in a multi user environment, where the idea you are using here will not work: if two users go for a reservation number at the same time, there is a very, very good chance that they will both get the same value.
Where are you creating this reservation ID, and why aren't you keeping the value from there?

这篇关于我在进行计算时无法保留该值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！