文本框为空时输入空值 [英] Enter null value when text box is empty

问题描述

我尝试过不同的方法，但没有一种方法可以使用：

I have tried different method to do this but none is working:

<pre lang="c#">
string strListOthLog = ((TextBox)fvAddBookingInfo.FindControl("txtOtherLogList")).Text;
string strComment = ((TextBox)fvAddBookingInfo.FindControl("txtComment")).Text;
.......
 cmd.Parameters.Add("@other_logon_list", SqlDbType.NVarChar).Value = string.IsNullOrEmpty(strListOthLog) ? (object)DBNull.Value : strListOthLog;
   
if (string.IsNullOrEmpty(strComment))
            {
                cmd.Parameters.Add("@additional_comments", SqlDbType.NVarChar).Value = System.DBNull.Value;
            }
            else
            {
                cmd.Parameters.Add("@additional_comments", SqlDbType.NVarChar).Value = strComment;
            }

我的尝试：



System.DBNull.Value以不同的方式。

What I have tried:

System.DBNull.Value in different ways.

推荐答案

使用 null 而不是 DBNull.Value

use null instead of DBNull.Value

cmd.Parameters.Add("@other_logon_list", SqlDbType.NVarChar).Value = string.IsNullOrWhiteSpace(strListOthLog) ? null : strListOthLog;
cmd.Parameters.Add("@additional_comments", SqlDbType.NVarChar).Value = string.IsNullOrWhiteSpace(strComment) ? null : strComment;

DBNull.Value：

DBNull.Value:

DBNull.Value用于处理数据库。数据库列可以包含空值。但是，当在代码中将该数据选择到对象（例如DataTable）中时，就代码而言，有一个对象可供引用。但是，该对象包含数据库中空值的表示。因此，DBNull.Value存在以表示该区别。它基本上意味着这里有一个C＃对象从数据库中获取一个值，但该值为空。

DBNull.Value is for the purpose of working with databases. A database column can contain a null value. However, when that data is selected into an object (such as a DataTable) in code, there is an object there to reference as far as the code is concerned. However, that object contains a representation of a null value from the database. Thus, DBNull.Value exists to represent that distinction. It basically means "There is a C# object here which grabbed a value from a database, but that value is null."

参考 null vs DBNull.Value [ ^ ]

此代码将起作用

This code will work

if (strListOthLog == "")
  cmd.Parameters.AddWithValue("@other_logon_list", DBNull.Value);
else
  cmd.Parameters.AddWithValue("@other_logon_list", strListOthLog);

谢谢大家的帮助。我一次尝试了上述所有方法，但没有成功输入空值而不是表格中的空白空格。最后我通过执行以下操作来实现它：

在存储过程中，我为不需要的字段设置默认值null（用户可以选择不输入值）。

@additional_comments varchar（500）= null

然后在lbInsert_Click事件中我有以下内容：

string strComment =（（TextBox）fvAddBookingInfo.FindControl（txtComment ））。文字;

....

if（strComment！= String.Empty）

{

cmd.Parameters.Add（@ additional_comments，SqlDbType.VarChar）.Value = strComment;

}

这对我有用。

再次感谢大家的支持。

I thank you all for helping me. I tried all the above mentioned ways one at a time and was not successful entering null value instead of blank empty space in a table. Finally I got it worked by doing the following:
In the stored procedure I set the default value null for the fields that are not required (user may choose not to enter a value).
@additional_comments varchar (500) = null
Then in the lbInsert_Click event I have following:
string strComment = ((TextBox)fvAddBookingInfo.FindControl("txtComment")).Text;
....
if (strComment != String.Empty)
{
cmd.Parameters.Add("@additional_comments", SqlDbType.VarChar).Value = strComment;
}
This is working for me.
Thanks again to all of you for your support.

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