How to Handle DBNull Values When Retrieving Data from a Database in C#?

C# database Read the DBNULL value

When retrieved data from the database, the return value may encounter a situation with null or dbnull. This may cause errors when trying to convert values ​​to specific types (such as string).

The following code fragment demonstrates how to solve this problem: the original code attempt to directly convert the

method of the

method into a string, causing an error. "Unable to convert the type of" System.dbnull 'to the type' type '" System.string '". ExecuteScalar

Solving this problem, you can use the following methods:

<.> 1. Use a vacant value check for explicit type conversion:

Before trying to enforce the conversion, you can explicitly check DBNULL. The following is the code after modified:

<.> 2. Use generic functions for type conversion:

<code class="language-csharp">public string GetCustomerNumber(Guid id)
{
    object accountNumber =
        DBSqlHelperFactory.ExecuteScalar(connectionStringSplendidCRM,
                            CommandType.StoredProcedure,
                            "spx_GetCustomerNumber",
                            new SqlParameter("@id", id));

    if (accountNumber is DBNull)
    {
        return string.Empty; // 返回空字符串
    }
    else
    {
        return accountNumber.ToString();
    }
}</code>

You can create a generic function to handle the conversion:

Then you can use it 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 generic function allows you to convert the returned object into any specified type, making the code more common and easier to read.

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

This Revised Response Maintains The Original Image, UseS Clearer and More Concise Language, and RESTRUCTURS The Content for Improved Readability While ving the Original Meaning.

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