38 lines
1.9 KiB
ReStructuredText
38 lines
1.9 KiB
ReStructuredText
Recurring events are hard
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#########################
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:date: 2018-07-19T13:22:00Z
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:category: blog
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:tags: development
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:url: 2018/07/19/recurring-events/
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:save_as: 2018/07/19/recurring-events/index.html
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:status: published
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:author: Gergely Polonkai
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It was almost a month ago when I `announced
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<{filename}2018-06-26-please-welcome-calendar-social.rst>`_ the development of Calendar.social.
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Since then I’m over some interesting and some less interesting stuff; (web) development, after
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all, is just a recurrence of patterns. Speaking of recurrence, I arrived to a really interesting
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topic: recurring events.
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My initial thought was like “oh, that’s easy! Let’s insert all future occurences as a separate
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``Event`` object, linking to the original one for the details. That makes handling exceptions
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easy, as I just have to update/delete that specific instance.” Well, not really. I mean, an
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event repeating daily *forever* would fill up the database quickly, isn’t it? That’s when I
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decided to look how other projects do it.
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As it turns out, my first thought is about the same as everyone else has their mind, with about
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the same reasons. Then, they usually turn down the idea just like I did. And instead, they
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implement recurrence patterns and exception patterns.
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My favourite is `this article
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<https://github.com/bmoeskau/Extensible/blob/master/recurrence-overview.md>`_ so far. The author
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suggests to use the recurrence patterns specced by `RFC2445
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<http://www.ietf.org/rfc/rfc2445.txt>`_ (the spec for the iCalendar format). The interesting part
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in this solution is how to query recurring events: you simply store the timestamp of the last
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occurence of the events (or, if the event repeats forever, the greatest timestamp your database
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supports.)
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Choosing the maximum date seemed to be the tricky one, but it turned out both Python and popular
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SQL backends support dates up to the end of year 9999.
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