如何处理dbnull错误 [英] How to handle dbnull errors

问题描述

Hello Everyone，



考虑到下面的内容，当出现错误（例如DBNULL错误）并且你点击没问题时，其他事件（例如a按钮单击）变得没有响应，有没有办法我可以处理此错误消息，因此它不会影响其他事件。谢谢。



我尝试了什么：

尝试
 {
 string selectcom7 = @select sum（inv）as grayear from grawu 
其中StaffNumber = @ staffid和DATEPART（年，日期）< @year; 
 SqlCommand comm7 = new SqlCommand（selectcom7，connection）; 
 comm7.Parameters.AddWithValue（@ staffid，txtstaffid.Text）; 
 comm7.Parameters.AddWithValue（@ year，cmbyear.Text）; 
 
 connection.Open（）; 
 SqlDataReader dr7 = comm7.ExecuteReader（）; 
 //字符串值; 
 
 
 
 if（dr7.Read（））
 {
 if（dr7 [prevyear] == null）
 { 
 previnvestment = Convert.ToDecimal（0.00）; 
} 
 else 
 {previnvestment = Convert.ToDecimal（dr7 [prevyear]）; } 
 
 
 // previous = Convert.ToString（dr7 [prevyears]）; 
 
} 
 else 
 {
 MessageBox.Show（No Previous data found）; 
 
} 
 
} 
 catch（exception ex）
 {
 MessageBox.Show（From Previous Balance：+ ex.Message ）; 
} 
最后
 {
 connection.Close（）; 
 
} 

解决方案

有一个特定的DBNull来处理数据库中的空值，因为null是一个.net null并且有不同的含义。

 if（dr7 [prevyear] == DBNull.Value）

Quote：

if（dr7 [prevyear] == null）

{

previnvestment = Convert.ToDecimal（0.00）;

}

else

{ previnvestment = Convert.ToDecimal（dr7 [prevyear]）; }

以上代码集应替换为

 double.TryParse（（dr7 [prevyear] + ），预先投资）; 
 

参考 Double.TryParse方法 [ ^ ]



如果你想检查null / DBNull值你应该使用这个<如果（dr7 [prevyear]！= null&& dr7 [prevyear]！= DBNull.Value）
{

}

Hello Everyone,

considering the below, when an error(such as the DBNULL error) gets popped up and you clicked okay,other events(such as a button click) becomes unresponsive, is there a way I can handle this error message so it doesn't affect other events. Thank you.

What I have tried:

try
            {
                string selectcom7 = @"select sum(inv) as prevyear from grawu 
                                      where StaffNumber=@staffid and DATEPART(year,Date)<@year";
                SqlCommand comm7 = new SqlCommand(selectcom7, connection);
                comm7.Parameters.AddWithValue("@staffid", txtstaffid.Text);
                comm7.Parameters.AddWithValue("@year", cmbyear.Text);

                connection.Open();
                SqlDataReader dr7 = comm7.ExecuteReader();
                //string value;

               

                if (dr7.Read())
                {
                    if (dr7["prevyear"] == null)
                    {
                        previnvestment = Convert.ToDecimal(0.00);
                    }
                    else
                    { previnvestment = Convert.ToDecimal(dr7["prevyear"]); }
                    

                    //previous = Convert.ToString( dr7["prevyears"]);
                    
                }
                else
                {
                    MessageBox.Show("No Previous data found");
                    
                }

            }
            catch (Exception ex)
            {
                MessageBox.Show("From Previous Balance :" + ex.Message);
            }
            finally
            {
                connection.Close();
                
            }

解决方案

There is a specific DBNull to handle nulls from the database as "null" is a .net null and has a different meaning.

if (dr7["prevyear"] == DBNull.Value)

Quote:

if (dr7["prevyear"] == null)
{
previnvestment = Convert.ToDecimal(0.00);
}
else
{ previnvestment = Convert.ToDecimal(dr7["prevyear"]); }

The above set of codes shall be replaced by

double.TryParse((dr7["prevyear"]+""),out previnvestment);

refer Double.TryParse Method [^]

if you want to check null/DBNull values you shall use this

if (dr7["prevyear"] != null && dr7["prevyear"]!= DBNull.Value)
           {

           }

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