How Can I Effectively Handle 'Unable to Cast Object of Type 'System.DBNull' to Type 'System.String'' Errors in C#?

Clever solution to "Cannot cast an object of type 'System.DBNull' to type 'System.String'" error

When trying to convert a DBNull value to a string, you often encounter the error "Cannot cast an object of type 'System.DBNull' to type 'System.String'". One way to handle this is to use a conditional statement that returns the empty string if the value is DBNull. However, this method is tedious and error-prone.

A more elegant solution is to use a generic function to handle the conversion from the database value to the required type, like this:

<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 receives an object as input and returns the converted value in the required type (in this case, string). How to use:

<code class="language-csharp">object accountNumber = 
          DBSqlHelperFactory.ExecuteScalar(connectionStringSplendidmyApp, 
                          CommandType.StoredProcedure, 
                          "spx_GetCustomerNumber", 
                          new SqlParameter("@id", id));</code>

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

By using this generic function, you can simplify your code and eliminate the need for conditional checks, ensuring type safety and reducing the possibility of errors.

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