Specifying the value format for a DateTimeInput using type=datetime-local, especially when using inline formsets

[bnmng]

I think I found a fix to a bug that I don't know was affecting anyone other than me.

You can see a better formatted version of what I've typed below at https://bnmng.wordpress.com/2022/01/22/make-sure-the-widget-is-correct-in-a-django-inline-model-formset/

TL;DR: For a DateTimeInput widget where type=’datetime-local’, specify the default format to include the T in the middle of the date-time string:

widgets={ 'when':forms.DateTimeInput( format='%Y-%m-%dT%H:%M:%S', attrs={'type':'datetime-local'} ), ... }

This was driving me crazy!

I had a model inline formset using a form:

forms.py:

TicketNoteFormset = inlineformset_factory(Ticket, TicketNote, form=TicketNoteForm, extra=10)

The specified form (TicketNoteForm) had a widget specified for a DateTime field:

forms.py:

class TicketTicketNoteForm(forms.ModelForm): class Meta: model = TicketNote fields = [ 'when', 'text', ] widgets={ 'when':forms.DateInput(attrs={'type':'date'}), 'text':forms.TextInput(attrs={'class':'len100'}) }

My mistake was using DateInput for the field ‘when’, which was a DateTimeField, not a DateField
models.py:

class TicketNote(models.Model): when = models.DateTimeField( 'when', default=datetime.now, help_text='The date that the note was submitted' )

In the HTML forms, the initial value, as expected, was a date-time value but the value attribute of the field was a date value without the time

<input type="date" name="ticketnote_set-0-when" value="2022-01-22 06:52:09" id="id_ticketnote_set-0-when"> <input type="hidden" name="initial-ticketnote_set-0-when" value="2022-01-22 06:52:09" id="initial-ticketnote_set-0-id_ticketnote_set-0-when">

The difference between initial and non-initial caused a record to be created even if the form was blank

But it was still broken after I fixed it

Leaving out the widget declaration works, but then I just get a plain text field and I want to take advantage of the browser’s popup calendar

I thought I had the problem fixed by specifying the widget as

forms.py:

DateTimeInput(attrs={'type':'datetime-local'}),

but that’s still giving me some problems. It worked fine in Firefox, but Chrome ignored the value attribute. So in Chrome

<input type="datetime-local" value="2022-01-01 08:01:00">

displays a blank datetime input and submits an empty string if not updated

I’ll update if I find a good solution.

Update: This works in Firefox and Chrome:
forms.py:

widgets={ 'when':forms.DateTimeInput( format='%Y-%m-%dT%H:%M:%S', attrs={'type':'datetime-local'} ), ... }

What Chrome was rejecting was having the value specified without the T between the date portion and the time portion. Django was producing the value without the T. By adding the format argument, I was able to make Django produce a default value that Chrome accepts.