How to handle null for a allow-null datetime field (DB) in our program?

Question

How could we handle null for a datetime field (got from SQL Server) in our program in c#?

Marc Gravell · Accepted Answer · 2009-08-29 09:01:40Z

There are 3 common approaches here;

if you are talking about object (perhaps as you fetch it from a data-reader), then DBNull.Value can represent null. I don't tend to let this out of the data-layer, though
due to .NET 1.1 history, DateTime.MinValue is commonly interpreted as null; a magic number, maybe - but it works and is supported by most data-binding etc
in .NET 2.0, Nullable<T> means you can use DateTime? - i.e. a nullable-of-DateTime; just use DateTime? where-ever you mean a DateTime that can be null, and you can give it a value of null or a valid DateTime.

Some other thoughts on data-access and nulls:

when passing to a SqlCommand you must use DBNull.Value, not null - see below
when reading from a data-reader, I tend to check reader.IsDbNull(ordinal)

command stuff (with Nullable<T> as the example):

param.Value = when.HasValue ? (object)when.Value : DBNull.Value;

Noon Silk · Accepted Answer · 2009-08-29 09:23:14Z

3

Use DateTime?

What problem are you having, specifically?

-- Edit

Just so it's clear, that's a Nullable DateTime object, not a question :)

DateTime? t = null;

-- Edit

Responding to comment, check it like so:

DateTime? theTime;

if( table["TheColumn"] == DBNull.Value ){
    theTime = null;
} else {
    theTime = (DateTime) table["TheColumn"];
}

answered Aug 29, 2009 at 9:01

Noon Silk

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3 Comments

I can not cast object (a column of DataRow) to DateTime .

Responded via edit. You just need to check if it is equal to DBNull.Value.

Okay ... You may like to post how you've solved it and mark it as accepted, so it helps anyone else who searches.