Date and Time Handling in 3.0

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In version 3.0 date and time handling has been improved. The most important change is that server operations now use the time zone of the user instead of the server time zone. Previously operations like generating documents, exporting to Excel/CSV and date computations in microflows/OQL all used the server time zone. This is fine if the server and all users of your application are in the same time zone. If they are not, however, generated output can contain unexpected results.

Relevant time zones

There are three time zones that come into play in a Mendix application:

  1. User/client: The time zone where the client is running is used for presenting dates and times to the end user. The time zone is now (optionally) stored with each user to properly deal with daylight saving time. If the time zone is not set daylight saving time (DST) is not applied.
  2. Coordinated Universal Time (UTC): The platform stores all dates in the UTC time zone. This is a time standard that is often used in servers to provide an unambiguous date format. It does not change with a change of the seasons (DST). Every time a date or time is presented to the user it is localized to the time zone of the client unless specified differently.
  3. Server: The time zone that the server is running in is only used for scheduling the time at which scheduled events run. When defining a scheduled event you can choose whether you want to use server time or UTC time. For everything else, the server time is irrelevant.

For brevity we will call these time zones user time, UTC and server time.

Changes

The server needs to know the time zone of each user. Unfortunately, the web browser cannot report this information. It only reports the current offset to UTC. This is not enough to determine the exact time zone and properly deal with daylight saving time of future and past dates. For this reason web applications often offer you the option of setting your time zone and we have now built this option into Mendix, too. You can explicitly set a time zone for each user and this time zone is then used for server operations.

The entity TimeZone has been added to the System module along with an association between User and TimeZone. The TimeZone entity has three attributes: a code (based on the Olson database), a description suitable for showing to the user (“(GMT-05:00) New York”) and a raw offset that is using for sorting the list of time zones.

In the Administration module the Account_NewEdit form adds a time zone selector to set the time zone of the user. By default, the form MyAccount does not have this selector. It is the administrator’s task to correctly set the time zone. You can add it yourself if you want your end users to be able to set their time zone.

The Modeler adds a setting to the project Settings dialog. On the ‘Model’ tab you can specify a default time zone. This time zone is used for new users, but it is also applied to all users that do not have a time zone yet when starting your application.

Existing projects

To make use of the new date/time handling you have to take some action after converting your existing project. Those actions depend on the type of the project: single time zone or multiple time zone. In a single time zone project all users are in the time zone or they are at least willing to use the same time zone. The time zone of the server is not important, so a project is still single time zone if all users are in the Netherlands but the server is in England. Multiple time zone projects have users in different time zones. Let us see what you need to do in each case.

Single time zone project

If you do nothing in a single time zone project where the server is also in that time zone the situation for server operations is actually slightly worse than before. Users will not have a time zone and if that is the case the server uses the current offset from UTC sent by the web browser. This offset is not enough to determine the exact time zone and this means that daylight saving time (DST) will not be taken into account. In practice this means that dates and times in the future and past - past DST changes - are one hour off.

To make sure that all users have their time zone set, you have to set the default time zone in the project settings in the Modeler. When the application is started again all existing users will get this default time zone. Also, when new users are created they will also get this default time zone automatically.

In summary, in a single time zone project all you have to do is to set the default time zone in the Modeler and you are done.

Multiple time zone project

If you do nothing in a multiple time zone project the situation for server operations improves automatically. Before, the server time zone would be used for operations like generating Excel exports and other documents. This meant that if a user in China generated a report and the server was in the United States dates and times would be way off. With the date/time handling in 3.0 the server will at least use the browser’s UTC offset. Only daylight saving time will not be handled properly yet. To get proper DST handling as well, the time zone of users needs to be set.

There are several things you can do in a multiple time zone project:

  • Nothing. If you do nothing server operations will use the user’s current UTC offset and this is a reasonable approximation of actually setting the time zone. Only DST will not be handled properly.
  • Allow the users to set their own time zone. Add the time zone reference selector to the form with which users can manage their own account, by default MyAccount in Administration. When doing this, take note that a timezone will only effectively be updated after a user logged out and back in.
  • The administrator sets the time zone. Add the time zone reference selector to the form with which the administrator manages accounts, by default Account_NewEdit in Administration. If the application does not have too many users this is a viable solution.
  • Automatically set the time zone by using a microflow. If your application is used in few time zones and you can automatically determine which users should which time zone you can write an after startup microflow to set the time zones. For example, if the application is used in the United States and in the Netherlands and all users in the United States have their language set to American English and all users in the Netherlands have their language set to Dutch a microflow can loop through all users and set the time zone based on the language code of the user.

Anonymous users

If your application is accessible without signing in, those anonymous users will get the default time zone that is set in the Modeler. If no time zone is set in the Modeler they will use the offset reported by the browser. Only DST for dates in the future and past will not be handled properly.

To localize or not to localize

Per attribute of type DateTime you can specify whether you want the date and time to be localized. This is not a new feature but worth mentioning on this page. Both localized and non-localized attributes are stored in UTC but only localized attributes are converted to the time zone of the user when displaying their value. Use non-localized attributes if you are not interested in the time component (e.g. birthdays) or if you want a date to look exactly the same all over the world.

See the documentation of the Localize property of Attributes for more information.

Tokens

Tokens for referring to specific moments like [%BeginOfCurrentDay%] now refer to the user time zone. Where it makes sense, UTC versions of tokens have been added, e.g. [%BeginOfCurrentDayUTC%]].

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