Comparing DateTime variable to DateTime data type column with Null values in it

Question

I have to do a c# search on records in an array from a sql server db using 3 data elements. One of the data elements has to be a DateTime element in a column called DateOfBirth. Unfortunately there are a lot of null values in this column and I can't figure out how to compare a DateTime variable to a field with NULL values. I see a lot of answers that appear to be close to what I need here, but nothing has helped. Thanks for any help, This has been my format.

if ((DateTime)dt == (DateTime)temp[i].Individual.DateOfBirth)
    GlobalNum3.bnum3 = 1;

So what happens with this code? Do you get a NullReferenceException? What are the compile time types of dt and DateOfBirth? — Charles Mager
– Charles Mager, Commented May 31, 2015 at 19:35
would it be an option to alter the SQL query so that entries with NULL datetimes are excluded? You could then process those entries in a seperate method. Something like ...WHERE DateOfBirth IS NOT NULL [...] would do the job. — Steffen Winkler
– Steffen Winkler, Commented May 31, 2015 at 19:45

David Arno · Accepted Answer · 2015-05-31 20:04:39Z

1

I'm assuming that dt is already a DateTime, in which case it can't be null (DateTime is a struct) and there's no need to cast it.In addition, either temp[i].Individual.DateOfBirth is a DateTime too and so cannot be null either, or it's a Nullable<DateTime>.

Assuming both are DateTimes, DB nulls will be set to DateTime.MinValue, so just compare the values:

if (dt == (DateTime)temp[i].Individual.DateOfBirth)
{
    GlobalNum3.bnum3 = 1;
}

However, if temp[i].Individual.DateOfBirth is a Nullable<DateTime>, it might be null, or might simply have no value, so use it like this:

var possibleDateOfBirth = temp[i].Individual.DateOfBirth;
if (possibleDateOfBirth != null &&
    possibleDateOfBirth.HasValue &&
    dt == possibleDateOfBirth.Value)
{
    GlobalNum3.bnum3 = 1;
}

edited May 31, 2015 at 20:04

answered May 31, 2015 at 19:39

David Arno

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4 Comments

Steffen Winkler Over a year ago

A DateTime in .NET can't be null. It's DateTime.MinValue. (DateTime is a struct type).

David Arno Over a year ago

@SteffenWinkler, yep, that's what I said "I'm assuming that dt is already a DateTime, in which case it can't be null"

Steffen Winkler Over a year ago

in that case I don't get your if statement :/

David Arno Over a year ago

@SteffenWinkler, hmm, I see what you mean. I only half thought through the DateTimes. temp[i].Individual.DateOfBirth either is a DateTime and so can't be null or must be a Nullable<DateTime>. I'll update the answer.

T McKeown · Accepted Answer · 2015-05-31 19:41:13Z

0

If you are querying the DB then try testing the nullable .HasValue property like this:

if (temp[i].Individual.DateOfBirth.HasValue && dt == temp[i].Individual.DateOfBirth.Value)
{
   GlobalNum3.bnum3 = 1;
}

Obviously I'm assuming you are testing DateTime? properties.

answered May 31, 2015 at 19:41

T McKeown

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