what is the correct way to read from a datarow if the cell might be null

Question

I have the following code which seems to blow up if the column in the datarow (dr) is null. what is the correct way to parse out the value from the data row and handle null checks?

Person person = new Person()
{
    FirstName = dr["FirstName"].ToString(),
    LastName = dr["LastName"].ToString(),
    BusinessPhoneNumber = dr["BusinessPhone"].ToString(),

Answer 1

If the column is of type string, but is nullable, what about trying:

// FirstName must allow null
FirstName = dr["FirstName"] as string

or

// FirstName would be empty for a NULL in the database
FirstName = (dr["FirstName"] as string) ?? string.Empty 

Answer 2

I believe, the data cell beeing null cannot be the reason for your problem. Maybe the column doesn't exist, or any other error happened, or the DataRow itself is null and you should handle that. Look at the exception - "seems to blow up" is not a valid description of your problem.

The following explains that, but will also answer the question from the title for everyone else.

If the column value is null, an object System.DBNull is returned, and .ToString() returns an empty string, while (string) or as string return null.

So it makes no sense to check the returned item for ==null because that won't ever evaluate to true.

• If you accept empty strings as result, your code is already optimal, no need to handle the DBNull case.
• If you want to get null, change .ToString() to as string.
• If you want to handle it in any other way, use if (dr.IsNull("FirstName")) or do ==null on the target variable after the as string.

Answer 3

dr["FirstName"].ToString() will occasionally throw null pointer exceptions because you're trying to access ToString on a null object. Other than that, strings can be null, so really, if you know it's a string, and you don't mind that it's null, it'd be safe to do

FirstName = (String) dr["FirstName"]