Timezone Strategy

Question

I am building a MVC 3 application where the users may not be in the same time zone, so my intent was to store everything in UTC and convert from UTC to local time in the vie

Answer 1

You can use something like MomentJS to display dates/times. Helps with formatting and local times.

Answer 2

You could handle the problem of converting UTC to user local time by using website-wide DisplayTemplate for DateTime.

From your Views you would use @Html.DisplayFor(n => n.MyDateTimeProperty)

The second problem is tougher to tackle. To convert from user local time to UTC you could override the DefaultModelBinder. Specifically the method SetProperty. Here is a naive implementation that demonstrates the point. It only applies for DateTime but could easily be extended to DateTime?. Then set it up as your Default binder in the Global.asax

public class MyDefaultModelBinder : DefaultModelBinder
{
    protected override void SetProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor, object value)
    {
        //special case for DateTime
        if(propertyDescriptor.PropertyType == typeof(DateTime))
        {
            if (propertyDescriptor.IsReadOnly)
            {
                return;
            }

            try
            {
                if(value != null)
                {
                    DateTime dt = (DateTime)value;
                    propertyDescriptor.SetValue(bindingContext.Model, dt.ToUniversalTime());
                }
            }
            catch (Exception ex)
            {
                string modelStateKey = CreateSubPropertyName(bindingContext.ModelName, propertyDescriptor.Name);
                bindingContext.ModelState.AddModelError(modelStateKey, ex);
            }
        }
        else
        {
            //handles all other types
            base.SetProperty(controllerContext, bindingContext, propertyDescriptor, value);
        }
    }
}

Answer 3

This is not possible automatically, you will have to do some manual work.

1 If you do not want to store user's timezone in db

1.1 Without masterpage: As csharptest.net suggested use java script's getDateTimeOffset() to get the timezone offset, set value in cookie, write a module to check for cookie if cookie is not present insert java script code and cookie using module.

1.2 Using masterpage: Same thing but no need to write module for checking.

2 Store user's timezone in db (best & easiest) No need to use javascript to get timezone just convert datetime according to user's timezone.

Answer 4

First this is mostly a duplicate of How can I determine a web user's time zone?, I agree with the majority vote there for this response:

The most popular (==standard?) way of determining the time zone I've seen around is simply asking the user herself. If your website requires subscription, this could be saved in the users' profile data. For anon users, the dates could be displayed as UTC or GMT or some such.

That being said the most common approach to automatically setting this value is to use javascript's Date getTimezoneOffset(). This can then be feed back to the server via a cookie or ajax request and stored with the user's profile, session, or cookie.

Ultimately I still think you should allow users to change this setting so that you can determine not just the UTC offset, but the actual timezone and daylight savings information as well.

When collecting input from users conversion to and from UTC via DateTime should suffice. DateTimeOffset is great when the client is managed code; however, with pure html/javascript it really isn't going to buy you much. Moreover the additional information of DateTimeOffset is not necessarily needed by most applications unless you intend to display to other users the originating timezone information.

I feel like just trying to be diligent about manually converting every input to UTC and manually converting every view to local time display will be very error prone and lead to difficult to detect bugs where the time is not converted to or from.

You should not depend upon diligence for correct date+time formatting and parsing. The .NET framework should handle this for you, for starters see "How to: Set the Culture and UI Culture for ASP.NET Web Page Globalization".

Closing remark

Frankly this is all a pain in the neck. We threw out the implementation some years ago and started transferring all date+time information in UTC, then we use Javascript to convert to local time and display format. This is really the only working model IMHO.