Avoiding duplicate Null Checks (Pass a User Control as a Parameter)

Question

I am working with an application that reads multiple dates from an Oracle database and assigns it to DateTimePickers.

dtpAdjSerDt.Value = dr.GetDateTime(iadj_service_date);

However, this assignment requires a null check as the values in the db could be null.

I would like to be able to create an extension method that returns a default value if the value is null.

public static DateTime fSafeGetDateTime(OracleDataReader reader, int colIndex)
{
    if (!reader.IsDBNull(colIndex))
        return reader.GetDateTime(colIndex);
    else
        return DateTime.Now;
}

There is one problem with this approach: If the db value is null then the DateTimePicker.Checked should be false. But using the strategy I suggested above it would be set to true.

Is there a way for me to do something like this:

public static DateTime fSafeGetDateTime(OracleDataReader reader, int colIndex, DateTimePicker control)
{
    if (!reader.IsDBNull(colIndex))
        return reader.GetDateTime(colIndex);
    else
    {
        control.Checked = false;
        return DateTime.Now;
    }
}

If this is not possible what would be the cleanest way (avoiding duplicate code) to accomplish this?

Answer 1

I suggest you just return a DateTime? and let the caller do the defaulting:

public static DateTime? SafeGetDateTime(this OracleDataReader reader, int colIndex)
{
    return reader.IsDBNull(colIndex) ? null 
                                     : (DateTime?) reader.GetDateTime(colIndex);
}

Now you can use:

DateTime fromReaderOrNow = reader.SafeGetDateTime(1) ?? DateTime.Now;

And if you need the control part:

DateTime? fromReader = reader.SafeGetDateTime(1);
if (fromReader == null)
{
    control.Checked = false;
}
DateTime fromReaderOrNow = fromReader ?? DateTime.Now;

If you really need to do that in multiple places, you can wrap up a method to do - and you won't be repeating the SafeGetDateTime code.

(I would encourage you to separate our your database code further from your UI code to start with, to be honest.)