RFC: Force conversion to/from a specific timezone

[phillipp]

Hi,
I'm maintaining a legacy app where the time zones are stored in the local time zone instead of UTC. I want to access the database via ecto. The problem is that it messes up the time by converting it to/from UTC and so everything breaks (there are literally hundreds of other clients that use the same database).

What is the best way to turn off the time zone conversion?

[phillipp]

I have implemented such behaviour in my fork (hard-coded for the time being: phillipp@475d0be). Would you like to integrate that? In that case, I'm not so sure what the best implementation would be. I thought about an extra type (like Timex.Ecto.LocalDateTime or sth.) but 99% of the module would be exactly the same code than the DateTime type. Can you think of a better way? I'm new to elixir and haven't fully grasped all the patterns that are possible and when to use what.

[bitwalker]

Probably the best way is to implement a Timex.Ecto.NaiveDateTime type which performs no conversions. Inputs will be converted to NaiveDateTime, and outputs will always be NaiveDateTime.

[bitwalker]

It's implementation can be very similar to Timex.Ecto.DateTime, just without the conversions to/from UTC.

[bitwalker]

I will put this on my TODO list, but it may be a week or two before I can get to it, if you'd like to take a stab at it and open a PR to collaborate on, I'd be glad to help with any questions.

[phillipp]

I have now tested two implementations:

a) one that converts the time from/to the local timezone, and that worked as I expected
b) one "naive" that does not convert before/after storing. This works for my own timestamps from the application that I converted explicitly to the local timezone before storing but not for the inserted_at and updated_at timestamps as they seem to be always generated in the UTC time zone.

At least for my use case I would need the first implementation. I'm not sure if that is a extremely specific case, but coming from Rails I wanted to match this behaviour:

    config.time_zone = 'Berlin'

    config.active_record.default_timezone = :local
    config.active_record.time_zone_aware_attributes = false

What do you think, is that too application-specific and should be part of my app or might there be a use case that should be supported by the lib? I think both might be possible...

[bitwalker]

Sorry it took me so long to get back to this - I am open to support such configuration, but I would suggest proposing it to the Ecto team first - it would be far better if it was an upstream config option, but if it's something they are not prepared to do in Ecto, I would be open to a PR for this project :)