How to Safely Cast DBNull Values to Strings in C#?

Convert null value to string in C#

Attempting to convert a System.DBNull object to System.String will usually result in an error, which usually occurs when retrieving data from the database. The original code attempts to cast the DBNull value directly to a string, causing the exception.

To resolve this issue, the code was modified to check for DBNull before converting to string:

<code class="language-csharp">if (accountNumber is DBNull)
{
    return string.Empty;
}
else
{
    return accountNumber.ToString();
}</code>

However, there is a more elegant solution using generic functions:

<code class="language-csharp">return ConvertFromDBVal<string>(accountNumber);</code>

The function is defined as follows:

<code class="language-csharp">public static T ConvertFromDBVal<T>(object obj)
{
    if (obj == null || obj == DBNull.Value)
    {
        return default(T); // 返回该类型的默认值
    }
    else
    {
        return (T)obj;
    }
}</code>

This function elegantly handles the conversion of a DBNull value to the desired type, returning the default value for that type if needed.

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