如何删除此例外？ [英] How to remove this exception?

问题描述

大家好，



我面临一个问题。可能是它非常简单但我无法解决它。

我得到例外：

Hello all,

I am facing one issue. Might be its very simple but i unable to solve it.
I am getting exceptions as :

There is already an open DataReader associated with this Command which must be closed first.

我的代码块是：

My Code block is :

protected void btnSubmit_Click(object sender, EventArgs e)
   {
       try
       {
           bool Ok = false;
           dt.OpenCon();
           string query = "select MA_Joining_Date from master_applicant where MA_App_Code='" + Session["U_Emp_Code"].ToString() + "'";
           SqlDataReader dr = dt.ExecuteReader(query);
           while (dr.Read())
           {
               DateTime date1 = DateTime.Parse(dr["MA_Joining_Date"].ToString());

                if (DateTime.Now.AddMonths(-6) < date1)
                   {
                     drdwnLeaveType.SelectedValue = "4";
                   }
           }

在同一个按钮上我还放了3个条件，一切正常。

on the same button i put another 3 conditions also, that all are working properly.

double NOD1 = Convert.ToDouble(ViewState["NoOfDays"].ToString());
            string qry = "select Status_ID from applicant_leavedetails where App_Code ='" + Session["U_Emp_Code"].ToString() + "' and Status_ID ='0'";
            string Status = dt.ExecuteScalar(qry);
            if (Status != "")
            {
                ScriptManager.RegisterStartupScript(Page, GetType(), "key1", "alert('Your previous application is pending');", true);
            }
               
            else if (NOD1 == 0)
            {
                ScriptManager.RegisterStartupScript(Page, GetType(), "key1", "alert('You have to select calculate leave days');", true);
            }
            else if (NOD1 <= 2 && drdwnLeaveType.SelectedIndex == 1)
            {
                ScriptManager.RegisterStartupScript(Page, GetType(), "key1", "alert('Please select CL Leave bellow that 2 days');", true);
                Ok = false;
            }

但不是条件不能正常工作。我该怎么办？

but not while condition is not working properly. what should i do??

推荐答案

处置你的对象！



错误信息非常明确：

已经有一个与此命令关联的开放DataReader必须先关闭。

这意味着你只能永远在任何单个连接上打开一个SqlDataReader。要打开一个新的，你 必须 先关闭旧的。

但你没有 - 你创建它，使用它，并且然后忽略它。因此，目前关闭它的唯一方法是垃圾收集器何时（以及如果）它会在您之后进行清理！所以当你完成它们时处理你的对象！



最简单的方法是通过使用 block：

Dispose your objects!

The error message is pretty explicit:
"There is already an open DataReader associated with this Command which must be closed first."
What it means is that you can only ever have one SqlDataReader open on any single connection. To open a new one, you must close the old one first.
But you don't - you create it, use it, and then ignore it. So the only way it will be closed at present is by the Garbage Collector when (and if) it gets round to cleaning up after you! So Dispose your objects when you are finished with them!

The easiest way to do this is via a using block:

string query = "select MA_Joining_Date from master_applicant where MA_App_Code='" + Session["U_Emp_Code"].ToString() + "'";
 using (SqlDataReader dr = dt.ExecuteReader(query))
 {
     while (dr.Read())
     {
         DateTime date1 = DateTime.Parse(dr["MA_Joining_Date"].ToString());

          if (DateTime.Now.AddMonths(-6) < date1)
             {
               drdwnLeaveType.SelectedValue = "4";
             }
     }
 }

这将关闭，处理并从范围中删除SqlDataReader，以免意外再次使用。



请为此，请不要那样做SQL！不要连接字符串以构建SQL命令。它让您对意外或故意的SQL注入攻击持开放态度，这可能会破坏您的整个数据库。请改用参数化查询。

This will Close, Dispose and remove the SqlDataReader from scope so it can't be accidentally used again.

And please, for your own sake, don't do SQL like that! Do not concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Use Parametrized queries instead.

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