Fix timezone shifts in news/posters/etc. (every forms.DateTimeField) - [closed]

[Juknum]

In GitLab by @tleb on Apr 17, 2020, 22:38

Merges datetime-hell -> master

The broken behaviour that was previously observed and that this MR tries to fix:

1. Create a news at /com/news/create with start date 2020-04-17 20:00:00 and end date 2020-04-17 22:00:00.
2. On /com/news/admin it gets displayed correctly.
3. However, if you edit it at /com/news/:id/edit it show 2020-04-17 18:00:00 and 2020-04-17 20:00:00 as start and end dates (assuming the current timezone is UTC+2).
4. If you submit which touching anything, the event/news/poster/other gets shifted by 2h (because it's summer time, only 1h if it's winter).

Timezone issue! What I understood from a (loooooong) debugging session (and django's doc) is that the database stores the datetime as UTC (2020-04-17 18:00:00 in our case). When it is displayed in a template, we use the localtime filter to adjust to the current timezone. However, a forms.DateTimeField is passed the datetime to display as a string. It was initially displayed as is (coming from the database) and therefore the UTC value was displayed. To solve this, the value which comes from the database must be parsed into a datetime to adjust the timezone.

It is done in three steps in the prepare_value(self, value) method which is used to prepare the database value to be displayed in the form (this MR changes nothing for the form validation and database insertion steps):

1. django.utils.dateparse.parse_datetime(string_dt), which returns a naive datetime storing the UTC time.
2. django.utils.timezone.make_aware(naive_dt, timezone.utc) which turns the naive datetime into an aware datetime which is "located" in UTC.
3. django.forms.utils.to_current_timezone(aware_dt) which turns an aware datetime into a naive datetime with the datetime which corresponds in the current timezone.

Example usage:

>>> from django.utils.dateparse import parse_datetime
>>> from django.utils import timezone
>>> from django.forms.utils import to_current_timezone

>>> parse_datetime("2020-04-17 18:00:00")
datetime.datetime(2020, 4, 17, 18, 0)
>>> timezone.make_aware(_, timezone.utc)
datetime.datetime(2020, 4, 17, 18, 0, tzinfo=<UTC>)
>>> to_current_timezone(_)
datetime.datetime(2020, 4, 17, 20, 0)

It is then turned back into a string to be displayed. It's important because otherwise it is automatically converted using the locale and on my PC it becomes 17/04/2020 20:00:00 (I'd say it's django's settings and not GNU/Linux's locale setting because mine is en_US.UTF-8) and the front-end doesn't support this format (the backend neither btw).

It's a WIP because I would like to have opinions on the approach and it needs to be tested by other people! An exhaustive list of pages this MR concerns:

• /club/:id/sellings: the sellings page of a club (id=1 for the AE club).
• /com/news/create: the news creation page.
• /com/news/:id/edit: the news edit page (create on on /com/news/create then test editing it).
• /counter/admin/cash_summary/list: by default there is nothing in local (but there is something on the prod). I don't know what needs to be done to have something in local.
• /election/add: the election creation page.
• /election/:id/edit: the election edit page (id=1 is populated).
• /subscription/stats: the subscription statistics page.
• /subscription: the subscription creation page.

I await (async hehe) your reviews. :)

[Juknum]

In GitLab by @tleb on Apr 17, 2020, 22:40

An aside: is core/templates/core/poster_list.jinja ever used? A global search brings up nothing. It seems like a duplicate (not exactly the same though) to com/templates/com/poster_list.jinja.

[Juknum]

In GitLab by @tleb on Apr 18, 2020, 08:56

added 1 commit

• b0780b42 - [com] simplify imports

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[Juknum]

In GitLab by @tleb on Apr 18, 2020, 13:18

fixes #102

[Juknum]

In GitLab by @sli on Apr 20, 2020, 18:29

Really nice job ! I was thinking, since we are making a wrapper in core, why also not harmonizing the input format so we don't have this wierd copy and paste all over the codebase :)

[Juknum]

In GitLab by @tleb on Apr 21, 2020, 08:47

added 1 commit

• 85692edf - TzAwareDateTimeField: input_formats and widget have default values

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[Juknum]

In GitLab by @tleb on Apr 21, 2020, 08:49

Done! I did it through default values in the constructor.

[Juknum]

In GitLab by @tleb on Apr 21, 2020, 09:00

added 1 commit

• 3cebe92c - fix errors on TzAwareDateTimeField (should not be used for DateField like date of birth)

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[Juknum]

In GitLab by @sli on Apr 21, 2020, 17:57

Commented on core/views/forms.py line 409

You can also do

def __init__(self, input_formats=["format"], widget=SelectDateTime, **kwargs):

[Juknum]

In GitLab by @sli on Apr 21, 2020, 17:58

Except for my last comment, really nice job, if you could rename your commit to match our pseudo naming convention that would be nice (module_touched1/module_touched2: change).

[Juknum]

In GitLab by @sli on Apr 22, 2020, 23:16

Moved to https://ae-dev.utbm.fr/ae/Sith/-/merge_requests/270

[Juknum]

In GitLab by @sli on Apr 22, 2020, 23:16

closed

[Juknum]

In GitLab by @skia on Sep 29, 2021, 15:53

mentioned in commit 007157e2e8aae7b2313614a65805b27090e6dffd