要在c＃.net中将billId值初始化为Billid ='BID0'

问题描述

我曾经从我的表中增加BillId Hbill.I调用increment（）来增加我的账单，如BID1，BID2 .....下面的代码工作但是当输入第一条记录时，它显示错误，因为billid是null。我怎样才能将billId值初始化为Billid ='BID0'或者在启动时设置默认值的任何其他方式。

i used to increment the BillId from my table Hbill.I called the increment() to increase my billid like BID1,BID2..... The below code is working but when entering the first record,its showing error since the billid is null.How can i initialize the billId value as Billid='BID0' or any other way to set the default value while starting.

public void increment()
    {
        con.Open();           

        SqlCommand cmd = new SqlCommand("select Max(billid) from hbill ", con);
        SqlDataReader dr = cmd.ExecuteReader();

            while (dr.Read())
            {
                id = dr[0] as string;

                //department = reader[1] as string;

            }

            cur_id = IncrementID(id, 3);                       


    con.Close();
}


static string IncrementID(string startValue, int numNonDigits)
        {
            string nonDigits = startValue.Substring(0, numNonDigits);
            int len = startValue.Length - numNonDigits;
            int number = int.Parse(startValue.Substring(numNonDigits));
            number++;
            if (number >= Math.Pow(10, len)) number = 1; // start again at 1
            return String.Format("{0}{1:D" + len.ToString() + "}", nonDigits, number);
        }

推荐答案

SqlCommand cmd = new SqlCommand("select Max(billid) from hbill ", con);
        SqlDataReader dr = cmd.ExecuteReader();
          if(dr.HasRows)
          {  
            while (dr.Read())
            {
                id = dr[0] as string;
 
                //department = reader[1] as string;

            }
 
            cur_id = IncrementID(id, 3);                       
          }
          else
          {
             id='BID0'
           cur_id = IncrementID(id, 3);
          }
   
   if(!con.IsClosed)
   {
    con.Close();
   }

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