Nullable Dates

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I have a start and end date in my application. If a user does not know their
dates yet, I want them, they will be null in the DB and I want them to be
blank in the application. So, I'm trying to figure out how to use a nullable
date, and want to return it in my method.

I tried to cast the output parameter, but I get a run-time cast error:
return new TimeLine((DateT ime?)command.Pa rameters["@startDate "].Value,
(DateTime?)comm and.Parameters["@endDate"].Value);
Then I changed to the code to what you see below, and it worked. But I am
wondering is there a better way to do this when working with nullable dates?

DateTime? startDate;
DateTime? endDate;

if (command.Parame ters["@startDate "].Value is DBNull)
startDate = null;
else
startDate = (DateTime?)comm and.Parameters["@startDate "].Value;

if (command.Parame ters["@endDate"].Value is DBNull)
endDate = null;
else
endDate = (DateTime?)comm and.Parameters["@endDate"].Value;

return new TimeLine(startD ate, endDate);

[Jon Skeet [C# MVP]]

On Sep 13, 3:12 pm, Wannabe <Wann...@discus sions.microsoft .comwrote:

I have a start and end date in my application. If a user does not know their
dates yet, I want them, they will be null in the DB and I want them to be
blank in the application. So, I'm trying to figure out how to use a nullable
date, and want to return it in my method.

I tried to cast the output parameter, but I get a run-time cast error:
return new TimeLine((DateT ime?)command.Pa rameters["@startDate "].Value,
(DateTime?)comm and.Parameters["@endDate"].Value);

Then I changed to the code to what you see below, and it worked. But I am
wondering is there a better way to do this when working with nullable dates?

The simplest way would be:

DateTime? startDate = command.Paramet ers["@startDate "].Value as
DateTime? ;
DateTime? endDate = command.Paramet ers["@endDate"].Value as
DateTime? ;

That will work, *but* it will give you null for start/end dates which
are neither DBNull nor DateTime. In other words, it will hide the
error. If you want more rigour, I'd write a helper method to convert
object to DateTime, throwing an exception if the parameter is neither
a DateTime nor DBNull.Value.

Jon

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

"Jon Skeet [C# MVP]" <sk***@pobox.co mwrote in message
news:11******** **************@ r34g2000hsd.goo glegroups.com.. .

On Sep 13, 3:12 pm, Wannabe <Wann...@discus sions.microsoft .comwrote:

>I have a start and end date in my application. If a user does not know
their
dates yet, I want them, they will be null in the DB and I want them to be
blank in the application. So, I'm trying to figure out how to use a
nullable
date, and want to return it in my method.

I tried to cast the output parameter, but I get a run-time cast error:
return new TimeLine((DateT ime?)command.Pa rameters["@startDate "].Value,
(DateTime?)com mand.Parameters["@endDate"].Value);

Then I changed to the code to what you see below, and it worked. But I am
wondering is there a better way to do this when working with nullable
dates?

The simplest way would be:

DateTime? startDate = command.Paramet ers["@startDate "].Value as
DateTime? ;
DateTime? endDate = command.Paramet ers["@endDate"].Value as
DateTime? ;

That will work, *but* it will give you null for start/end dates which
are neither DBNull nor DateTime. In other words, it will hide the
error. If you want more rigour, I'd write a helper method to convert
object to DateTime, throwing an exception if the parameter is neither
a DateTime nor DBNull.Value.

If the columns in the DB are of DateTime then it will work as expected.

[Jon Skeet [C# MVP]]

<"Ignacio Machin \( .NET/ C# MVP \)" <machin TA laceupsolutions .com>>

That will work, *but* it will give you null for start/end dates
which
are neither DBNull nor DateTime. In other words, it will hide the
error. If you want more rigour, I'd write a helper method to convert
object to DateTime, throwing an exception if the parameter is neither
a DateTime nor DBNull.Value.

If the columns in the DB are of DateTime then it will work as expected.

Indeed. I was just warning that if the columns were changed
inappropriately , it would fail silently (by returning null) rather than
screaming from the rooftops about the type being wrong :)

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too