You have it mostly correct.

TzDatetime.handle_datetime(cs, input_datetime: :start_time, datetime: :start_time)

I’d suggest a virtual field for the input separate to the field storing the utc_datetime, but this should work. Also you don’t need to require TzDatetime. There are no macros involved here so just calling the functions is enough.

The timezone field you’ll need to set somehow either by letting the user submit the value or adding it to the changeset based on other information your system has.

As for the original_offset: You shouldn’t need to care about that at all. It’s set by handle_datetime/2 and read by original_datetime/2. The latter will return different values if there’s a missmatch detected between the stored offset and the offset based on your current timezone database.

Nice. I works! Thank you!

Convert the start_time and end_time using Timex, shows the correct time

Thank you very much!

Please use original_datetime/2 to convert the utc_datetime back to your original timezone. It mostly does shift the timezone just like timex does, but you’ll be made aware if the timezone definitions changed to cause a different offset to the time when the datetime was stored. This will hardly ever happen for datetimes in the past, but is a valid problem to look for in future datetimes.

Is the :time_zone field in your changeset nil or set to something proper?