Develop Reference

Date Time Struct to deal with different time zones

I make struct name DateTimeZone , I set it to take the UTC time and I get it to take local time.
DateTimeZone time = DateTime.Now;//time will equal the UTC time
DateTime localTime= time; // local time will equal the Local time
the struct
public struct DateTimeZone
{
private DateTime dateTime;
// public DateTimeZone Value { get; }
public static implicit operator DateTimeZone(DateTime value)
{
return new DateTimeZone() { dateTime = value.ToUniversalTime() };
}
public static implicit operator DateTime(DateTimeZone value)
{
return value.dateTime.ToLocalTime();
}
}
My question : is there easiest way to implement this than struct?
and this struct have exception when i save in DB cause entity frame work,
so I need to make mapping every time I use struct , How I can make mapping in concise manner?

A few things:
Be careful with your naming. An object with a name like DateTimeZone would be expected to contain either 1) time zone information only, or 2) a date and time and time zone. Your object is only an encapsulation wrapper around DateTime, so it is neither of these things.
Implicit operations can be evil - especially if they change the meaning of the value you're working with. I don't recommend using them with date/time, unless you really know what you're doing. It will quickly become confusing to any user of this object as to what value you were actually working with.
The ToUniversalTime and ToLocalTime functions change their behavior based on the DateTimeKind assigned to the .Kind property of the DateTime objects you're working with. You seem to be creating an API in which DateTime is always local and DateTimeZone is always UTC, but DateTimeKind will get in the way of this idea.
As mentioned in comments, you might look into using Noda Time, which is a very solid and well-thought-out API. In Noda Time, the Instant type always represents UTC, and the LocalDateTime type always represents a timezoneless date and time. Time zones are represented by DateTimeZone (see the conflict with your name), and the ZonedDateTime type combines these, such that you have both instant-in-time information, local-time information, and the associated time zone.
You mentioned Entity Framework. Unfortunately, EF will not work directly with either your custom object, or with Noda Time. It does not have the ability to do simple type conversions. This has been requested, but not yet implemented. You can follow the work item for it here. A workaround you can use is "buddy properties", as described here. They're not fun, but they work. Mostly.
You may find it reasonable to just use DateTime, and call methods like ToUniversalTime or ToLocalTime manually, when needed. If you want EF to properly set DateTimeKind when loading from the database, see this answer.
Keep in mind that both ToUniversalTime and ToLocalTime work with the computer's local time zone where the code happens to be running. This works fine for desktop and mobile applications, but is rarely desired for web applications, because changing the time zone of the server could drastically affect the data. Consider instead working with a named time zone via the built-in TimeZoneInfo class, or with the DateTimeZone class in Noda Time.
Additional reading for you:
Daylight saving time and time zone best practices
The timezone tag wiki

Maybe you should try this one:
public struct DateTimeZone
{
public DateTime DateTime;
public static explicit operator DateTimeZone(DateTime dt)
{
return new DateTimeZone { DateTime = dt.ToUniversalTime() };
}
}
var time = (DateTimeZone)DateTime.Now;
var localTime = time.DateTime;

NodaTime: Replicating DateTime.Today

My service requests data from an external service that needs an argument for a particular date (doesn't need time information).
Until now, I've been using DateTime.Today (e.g. 10/24/2014 12:00:00).
I've moved to using NodaTime for improved testability but not sure of the best way to replicate this functionality:
public class SomeClass(IClock clock)
{
_clock = clock; //Injected at runtime, provides mockable interface
var localNow = _clock.Now.InZone(_serverTimeZone);
var today = localNow.ToDateTimeUnspecified().Date; //This close enough? Seems kinda long
}

To represent a date, you should use LocalDate rather than DateTime, ideally. So you want:
var localNow = clock.Now.InZone(serverZone);
var today = localNow.Date;
If you must use DateTime, then your current code is fine.
In Noda Time 2.0, this will be simpler due to a ZonedClock which is basically a composite of a clock and a time zone, allowing you to write:
// Or whatever...
private readonly ZonedClock zonedClock = clock.InZone(zone);
// Then later
LocalDate date = zonedClock.GetCurrentDate();
Noda Time 2.0 isn't ready for release yet, but I wanted to give you an idea of what's coming.

Difficulty comparing two DateTime instances

I'm writing a Unit Test class in C# (.NET 4.5). In one of the tests I'm checking the values of various properties after an instance of our class FeedbackDao is constructed. On construction, the FeedbackDate property of FeedbackDao is set to DateTime.Now.
FeedbackDao feedbackDao = new FeedbackDao();
// a couple of lines go here then I set up this test:
Assert.IsTrue(feedbackDao.FeedbackDate.CompareTo(DateTime.Now) < 0);
My assumption is that feedbackDao.FeedbackDate should always be just a little earlier than the current time returned by DateTime.Now, even if it's only by a millisecond, and my IsTrue test should always pass, but sometimes it passes and sometimes it fails. When I add a message like this:
Assert.IsTrue(feedbackDao.FeedbackDate.CompareTo(DateTime.Now) < 0,
feedbackDao.FeedbackDate.CompareTo(DateTime.Now).ToString());
the message sometimes reads -1 (meaning that FeedbackDate is earlier than Now) and sometimes reads 0 (meaning that the DateTime instances are equal).
Why is FeedbackDate not always earlier than Now? And, if I can't trust that comparison, how can I write a rigorous test to check the value of FeedbackDate when FeedbackDao is constructed?

My assumption is that feedbackDao.FeebackDate should always be just a little earlier than the current time returned by DateTime.Now, even if it's only by a millisecond.
What makes you think that? That would suggest that 1000 calls would have to take at least 1 second which seems unlikely.
Add to that the fact that DateTime.Now only has a practical granularity of about 10-15ms IIRC, and very often if you call DateTime.Now twice in quick succession you'll get the same value twice.
For the purpose of testability - and clean expression of dependencies - I like to use a "clock" interface (IClock) which is always used to extract the current system time. You can then write a fake implementation to control time however you see fit.
Additionally, this assertion is flawed:
Assert.IsTrue(feedbackDao.FeebackDate.CompareTo(DateTime.Now) < 0,
feedbackDao.FeebackDate.CompareTo(DateTime.Now).ToString());
It's flawed because it evaluates DateTime.Now twice... so the value that it reports isn't necessarily the same one that it checks. It would be better as:
DateTime now = DateTime.Now;
Assert.IsTrue(feedbackDao.FeebackDate.CompareTo(now) < 0,
feedbackDao.FeebackDate.CompareTo(now).ToString());
Or even better:
DateTime now = DateTime.Now;
DateTime feedbackDate = feedbackDao.FeebackDate;
Assert.IsTrue(now < feedbackDate,
feedbackDate + " should be earlier than " + now);

Your test is not that useful as it is, you're asserting that the value is less than DateTime.Now but that does not mean it was correctly set to the expected value. If the date time is not initialized it will have the DateTime.MinValue and that value will always pass the test.
This test is as valid as testing for feedbackDao.FeebackDate.CompareTo(DateTime.Now) <= 0 and with that you would not have the problem that motivated you to write this question.
You need to extract the dependency on DateTime.Now or use a mocking framework that supports mocking DateTime.Now and assert that the value is initialized to the correct one. You can check Microsoft Moles, now renamed to Fakes in VS 2012, which is the only mocking framework that I know that is free (kind of for the latest version, since it ships with VS and don't know if it is available on the express editions) and that will let you replace a call to DateTime.Now.
Update:
Without resorting to a mocking framework you could improve your test by doing something like this:
var lowerBoundary = DateTime.Now;
var dao = new FeedbackDao();
var upperBoundary = DateTime.Now;
Assert.IsTrue(dao.Date >= lowerBoundary && dao.Date <= upperBoundary);

When unit testing, I consider DateTime.Now to be an external dependency, and thus something needing to be mocked. What I've done in the past when testing scenarios involving DateTime.Now, I've just passed a Func<DateTime> in via the constructor of the class, which allows me to mock DateTime.Now during testing.
I prefer this over Jon Skeet's suggestion of using something like an IClock interface to wrap around the DateTime properties, just because the last time I did this, I felt silly making a new interface and class to wrap around a single property. If you're going to need to test around more than one of the static DateTime properties, I definitely agree with the IClock suggestion.
For example,
public class Foo
{
private readonly Func<DateTime> timeStampProvider;
public Foo(Func<DateTime> timeStampProvider)
{
this.timeStampProvider = timeStampProvider;
}
public Foo() : this(() => DateTime.Now)
{
}
public bool CompareDate(DateTime comparisonDate)
{
// Get my timestamp
return comparisonDate > timeStampProvider();
}
}
Then, during testing,
var testFoo = new Foo(() => new DateTime(1, 1, 2010));

I generally use a mock data to validate my logic. I evolve my test scenarios around the mock data. As suggested by DBM.
Mock data is a set of known data that is generally static or configurable. Common practice is to have a XML file with all the test data and load them as and when required. I can give you an example in our Project.

Try
Assert.IsTrue(feedbackDao.FeebackDate.CompareTo(DateTime.Now) < 1);
Or
Assert.IsTrue(feedbackDao.FeebackDate - DateTime.Now < someMarginOfError);
Time is generally fairly granular - often 10's of milliseconds IIRC.

Depending on your system, DateTime.Now is not updated every millisecond or tick, it is only updated periodically. Typically 10 ms or so. See here: How frequent is DateTime.Now updated ? or is there a more precise API to get the current time?

DateTime.Now isn't 100% accurate. It increases by around 130 ms(from personal experience per tick). So it's verry likely that if your method is fast enough the date will be equal to datetime.now and not smaller.
If you want a 100% accurate timer you should use the StopWatch class.
Msdn link to stopwatch

.Net DateTime Precision

within my .net domain object I am tracking each state transition. This is done by putting the state set into a state history collection. So later on, one can see an desc ordered list to find out which state was changed at what time.
So there is a method like this:
private void SetState(RequestState state)
{
var stateHistoryItem = new RequestStateHistoryItem(state, this);
stateHistoryItems.Add(stateHistoryItem);
}
When a new RequestStateHistoryItem is instantiated, the current date is automatically assigned. Like this:
protected IdentificationRequestStateHistoryItem()
{
timestamp = EntityTimestamp.New();
}
The EntityTimestamp object is an object containing the appropiate user and created and changed date.
When listing the state history, I do a descending order with Linq:
public virtual IEnumerable<RequestStateHistoryItem> StateHistoryItems
{
get { return stateHistoryItems.OrderByDescending(s => s.Timestamp.CreatedOn.Ticks); }
}
Now when a new Request is instantiated the first state Received is set in the constructor SetState(RequestState.Received). Then, without any delay and depending on some conditions, a new state Started is set. After some time (db operations) the state Finished is set.
Now when performing the descending ordering, the Received always is AFTER the Started state. When I am debugging slowly, or when putting a System.Threading.Thread.Sleep(1000) before setting the state to Started, the ordering works.
If not, as told above, the Started state's CreatedOn is OLDER then the Received CreatedOn date?!
TimeOfDay {17:04:42.9430318} FINSHED
Ticks 634019366829430318
TimeOfDay {17:04:39.5376207} RECEICED
Ticks 634019366795376207
TimeOfDay {17:04:39.5367815} STARTED
Ticks 634019366795367815
How can that be? I would understand if the received and start date is exactly the same, but I don't understand how it can even be BEFORE the other one?
I already tried new DateTimePrecise().Now, (see DateTimePrecise class) I found in another question. Same result.
Anyone knows what that could be?
Update
public virtual bool Finish()
{
// when I put the SetState(State.Received) from the constructor into here, the timestamp of finish still is BEFORE received
SetState(IdentificationRequestState.Received);
SetState(IdentificationRequestState.Finished);
// when I put the SetState(State.Received) after Finished, then the Received timestamp is BEFORE Finished
SetState(IdentificationRequestState.Finished);
SetState(IdentificationRequestState.Received);
var match = ...
if (match != null)
{
...
}
else
{
...
}
}

DateTime.Now is not accurate to the millisecond. It is only updated at larger intervals, something like 30 or 15 milliseconds (which is just the way Window's internal clock works, IIRC).
System.Diagnostics.Stopwatch is a more accurate way to measure time differences. It also doesn't have the overhead of UTC to local time conversions etc. The DateTimePrecise class uses a combination of DateTime and Stopwatch to give a more accurate time than DateTime.Now does.

You are retrieving the timestamp at an undetermined time before you add it to your collection.
The delay between retrieving it and adding it to the collection is variable - for example your thread may be pre-empted by the scheduler after getting the timestamp and before adding to the collection.
If you want strict ordering, you need to use synchronisation, something like the following every time you instantiate a history item:
lock(syncLock)
{
// Timestamp is generated here...
var stateHistoryItem = new RequestStateHistoryItem(state, this);
// ... but an indeterminate time can pass before ...
...
// ... it's added to the collection here.
stateHistoryItems.Add(stateHistoryItem);
}

Have you tried setting both the Received and Started timestamps via the same approach (i.e. moving the Received stamp out of the constructor and setting it via property or method to match how the Started status is set?).
I know it doesn't explain why, but constructors are somewhat special in the runtime. .NET constructors are designed to execute as fast as possible, so it wouldn't surprise me that there are some side-effects of the focus on performance.

Best way to compute UTC/local datetime conversion in a WCF client/server application

I've got a client/server application, written in WCF / C#3.5.
The server is in my local TimeZone, and clients are spreaded accross the world.
My current strategy is to use UTC DateTime everywhere on the server and in the database, and to let the clients handle correctly the UTC DateTimes they receive.
This means that everytime the client receives a message, its first task is to convert the DateTimes contained in the message from UTC to Local.
I've defined an interface, implemented by all my [DataContract] objects to help this task :
public interface IConvertToLocalTime {
void ConvertToLocalTime();
}
So I typically handle a message from the server this way :
public void ServerCallbackFoo(MyObject a, MyObject2 b)
{
a.ConvertToLocalTime();
b.ConvertToLocalTime();
// my business code goes there
}
This works fine, but I'm not very pleased with the fact that I've got to manually call the conversion method.
It seems to me that this task should be managed by the WCF framework. Am I missing something there? Is there a better way to automate the conversion ?

To my knowledge, WCF does not provide any kind of automation to aid time conversions, and personally, I wouldn't expect it to.
And I agree with you. Having to manually call the conversion routine is not the ideal. It doesn't "feel" elegant.
To me, a more elegant solution would be to "lazily" evaluate the DateTime as it is needed. Instead of providing a function that must be called to convert the UTC times to local times, put this logic inside each DateTime property's get function. That way, when the DateTime is retrieved from the object, it is automatically converted to local time.

I'm possibly not understanding the question, but wouldn't it be easier to use the built in DateTime.ToLocalTime and DateTime.ToUniversalTime as needed since you are using .NET for both the service and the client. You should be able to check the .Kind property to see if the DateTime is local or UTC.
DateTime test = DateTime.Now; //already local time
DateTime LocalTest = test.ToLocalTime();
DateTime UtcTest = test.ToUniversalTime();
You may also want to look at this SO Question regarding handling DateTime serialization.

You could make clients convert to/from local time precisely when presenting information to the user, and conversely do it first thing when reading user entered data. The rest of the client could then work with UTC.