I have a dataset with a DateTime field, which contains local server times. When this is rendered it has the "Z" (Zulu) timezone added to the json data.
So a value that is 2020/07/31@14:30:12.250 is rendered as 2020-07-31T14:30:12.250Z rather than the 2020-07-31T14:30:12.250+12:00 we would expect to see from the server time zone.
This means the time as rendered is actually incorrect by 12 hours !

The code that does the rendering is in the TMVCJsonDataObjectsSerializer.DataSetToJsonObject method. For DateTime fields it calls DateTimeToISOTimeStamp (in the MVCFramework.Serializer.Commons.pas unit) which calls DateToISO8601 passing through a hardcoded value of True for the second param of "InputIsUTC"
Because of this hard coded param all dates are assumed to be encoded to UTC with zero offset, so local dates are not handled correctly.

I can see a couple of ways to fix this:

• change the storage of the dates in the database from local to UTC. Unfortunately we do not control the database.
• change the call to DateToISO8601 to pass through False as the second param. This may break existing applications.
• add an additional param to DateTimeToISOTimeStamp to allow InputIsUTC to be specified, with a default value of True.
  This could be specified with a set of options that can be passed through to the Serialiser call (I can see other options that could be added over time for formatting).

Let me know what you think and I can mock up some potential changes with test cases.