Cannot change CheckboxSelectMultiple, FileInput, MultiWidget, SplitDateTimeWidget, and SelectDateWidget with model field default since Django 1.10.1

[Michael Käufl]

Since Django 1.10.1 (it worked in 1.10.0), it is not possible to change the value of a DateTimeField in the admin if the field has a default.

Changing the value and saving the object results in the old value still being in the database.

How to reproduce

I created a small ​example project to easily reproduce the problem.

It has a ​model ''Dummy'' with two DateTimeFields. One with and one without a default (django.utils.timezone.now). The ​admin is the default django.contrib.admin.ModelAdmin.

git clone https://github.com/michael-k/datetimefieldbroken.git && cd datetimefieldbroken
docker-compose build --pull
docker-compose run web migrate
docker-compose run web createsuperuser
docker-compose up -d

Head your browser to ​http://localhost:8023/admin/main/dummy/add/, login and create a new Dummy using Save and continue editing. Change the values all for input fields and press Save and continue editing again. The values of Dt with default are unchanged.

Patch that introduced the issue

We believe that ​PR 7068 (regarding issue 27039) introduced the problem, but did not validate this. Supposedly this happens because DateTimeField is split into two fields (date + time) in the admin.

We tried it however with Django 1.10.0 and it works just fine.

[Tim Graham]

​PR

[Tim Graham <timograham@…>]

In 3507d4e7:

Fixed #27186 -- Fixed model form default fallback for MultiWidget, FileInput, SplitDateTimeWidget, SelectDateWidget, and SplitArrayWidget.

Thanks Matt Westcott for the review.

[Tim Graham <timograham@…>]

In 0b59ea33:

[1.10.x] Fixed #27186 -- Fixed model form default fallback for MultiWidget, FileInput, SplitDateTimeWidget, SelectDateWidget, and SplitArrayWidget.

Thanks Matt Westcott for the review.

Backport of 3507d4e773aa9ff2336e7230ba231c4ba6eb568f from master

[Tim Graham]

As reported in #27291, CheckboxSelectMultiple is also affected.

[Tim Graham]

​PR for CheckboxSelectMultiple.

[GitHub <noreply@…>]

In 87c5e7e:

Refs #27186 -- Fixed model form default fallback for CheckboxSelectMultiple.

[Tim Graham <timograham@…>]

In f23c03e:

[1.10.x] Refs #27186 -- Fixed model form default fallback for CheckboxSelectMultiple.

Backport of 87c5e7efebd040aef0f0479ccf86877155bb5cea from master