#9739: Admin does not correctly prefill DataTimeField from URL -------------------------------+--------------------------------------- Reporter: gilhad | Owner: Fabian Binz Type: Bug | Status: assigned Component: contrib.admin | Version: 1.0 Severity: Normal | Resolution: Keywords: | Triage Stage: Accepted Has patch: 1 | Needs documentation: 0 Needs tests: 0 | Patch needs improvement: 1 Easy pickings: 0 | UI/UX: 0 -------------------------------+--------------------------------------- Comment (by Fabian Binz):
I've looked at this ticket for quite some time during and after the recent sprint at the Cologne Django Meetup. For now, I've come to the conclusion, that - while there are definitely ways to build the functionality that's requested in the ticket - it's actually quite hard to do that in a manner that's general enough to cover all cases. What follows is a lengthy discussion of my current understanding of the problem, partly to just have a record of this for myself, but maybe we could also discuss a way forward: 1. Handling of initial data for multi-value fields 2. Parsing of localized datetime strings 3. Deviation from the way HTML forms normally work The source of the "bug" is actually pretty simple: The SplitDateTimeWidget.decompress method expects its input to be a datetime object, which is not the case when the initial data is passed via a query parameter. According to the docs, this is a reasonable behavior, since the decompress method actually should only receive valid inputs (i.e. a datetime object). So, I guess it's not unreasonable to crash if passed a plain string. So, why is this contract violated in this case? Because the initial data specified via query parameters is passed verbatim - via a bunch of indirections - to the widget's decompress method, without any form of validation or parsing. Now, how could we actually parse or validate the input properly? In the case of a datetime field, I think we'd either have to settle on some standard way of formatting datetimes (datetime.isofromat seems reasonable as opposed to a comma- or space-separated representation discussed above) or we could take into account the DATETIME_FORMAT setting that the user has set. However, this doesn't really seem feasible. Fundamentally, I think the issue is that POST and GET data are not handled in a similar manner for MultiValueFields/MultiWidgets: Let's say we have a datetime field named "created_at". The SplitDateTimeWidget would render HTML similar to the following: <input name="created_at_0" ...> <input name="created_at_1" ...> Normally, we'd use query parameters like "created_at_0=2024-01-02" and "created_at_1=15:31:23" to pre-fill both the date and the time. For multi- value fields however, we expect that we can set both values using a single query parameter. When data is POSTed, we don't have that problem, since both inputs are simply separate values and can easily be passed to the MultiValueField.compress method. For my taste, having this difference between POST and GET does not make much sense and it would seem more consistent to just use the individual input names to pre-fill fields. This also enables partially pre-filling inputs, which is much harder when expecting to have a single representation of a value. But I also see the convenience of having a single URL parameter to set multiple fields. There are even test cases which kind-of test this behavior (though not for the SplitDateTimeWidget). So maybe an alternative would be to make the serialization/deserialization to/from string a part of the interface of the MultiValueField/MutliWidget classes, so that those methods can be used where needed. -- Ticket URL: <https://code.djangoproject.com/ticket/9739#comment:29> Django <https://code.djangoproject.com/> The Web framework for perfectionists with deadlines. -- You received this message because you are subscribed to the Google Groups "Django updates" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-updates+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/django-updates/0107018d3dcd1e44-b675a0b9-702d-430a-8d88-ec9e80e14ce2-000000%40eu-central-1.amazonses.com.