Handling UTC time within C#?

Question

I am not an expert on the internals of C# so this question might actually be downright silly. If so, please correct me. I have some data (in UTC format) taken out from a SQL server.

2011-03-26 11:03:58.000
2011-03-26 11:04:25.000
...

I am parsing this file inside C# and am using the following:

DateTime date = DateTime.Parse(value);

to fetch the value into the DateTimeobject. Now, I am subtracting some arbitrary time 6 hours from this time as follows:

date = date.Subtract(new TimeSpan(6, 0, 0));

And finally, I am writing this back into another file as follows:

output.WriteLine(date.ToString("yyyy-MM-dd HH:mm:ss.fff"));

Because I have not done any implicit conversions, the output is also UTC. My question is, is this kind of addition/subtraction of time allowed on the parsed date or do I need to do some UTC to C# specific conversion before being able to manipulate time? I am having difficulties wrapping my head around this. Would someone please clarify this?

EDIT: Attempt to write a concise question The original date is in UTC. I want to add/subtract some time and write it back in UTC. I want to know if I can manipulate the parsed date directly or I need to do some conversions i.e. tell C# explicitly that the date is in UTC format and then manipulate it and then tell it again to write back UTC date.

Answer 1

It doesn't really matter. A date is a date, no matter what time zone it's in. Unless you're converting it to a different time zone, .Net doesn't know or care what time zone it is.

If you want to, you can call DateTime.SpecifyKind(value, DateTimeKind.Utc).

Answer 2

You do not need to parse datetimes from SQL Server. The ADO.Net will return a SqlDateTime object for a datetime type column in a result. ORM libraries (LinqToSQL, Entity Framework etc) are also perfectly capable of mapping datetime type columns to DateTime properties. If you find yourself parsing a string, you're doing it wrong (not to mention all the implications of SET DATEFORMAT...)

As a note the operation you described can be performed straight on the server, eg. add one hour to an UTC datetime field and save it back as UTC datetime:

UPDATE table SET column = DATEADD(hour, 1, column) WHERE ...