[Django] #35696: ModelAdmin is overruling the fields of ModelForm

[Django]

#35696: ModelAdmin is overruling the fields of ModelForm
-------------------------------+--------------------------------------
Reporter: Jurrian Tromp | Type: Bug
Status: new | Component: Forms
Version: 4.2 | Severity: Normal
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------+--------------------------------------
It seems that in ModelForm both `field_order` and `Meta.fields` ordering
is being overruled by the admin change view. When rendering, the `form`
object initially has the correct order, but when `admin_form`
(django.contrib.admin.options:1826) is created, the `fieldsets`
(django.contrib.admin.options:1781) coming from `get_fieldsets()`
overrides the correct order in `form.fields`.

Something similar in #19514 has been reported before, more or less saying
that ModelAdmin order should be leading. The problem with this however is
that the reason you have a ModelForm here this way is because you try to
do something more specialized. Consider this:

{{{
class Message(models.Model):
some_readonly = models.CharField(...)
overruled_model_m2m_field = models.ManyToManyField(through=SomeModel,
...)

class MessageForm(forms.ModelForm):
some_form_field = forms.CharField()
overruled_model_m2m_field = forms.CharField()

field_order = ['some_form_field', 'overruled_model_m2m_field']

class Meta:
model = Message
fields = ['some_form_field', 'overruled_model_m2m_field']
exclude = ['some_readonly']

class MessageAdmin(admin.ModelAdmin):
readonly_fields = ['some_readonly']
form = MessageForm
}}}

**Resulting in the following unexpected behavior:**
1. For the fields MessageForm is ignored for the most part,
MessageAdmin.get_fields() is de-facto shown.
a. ModelAdmin `readonly_fields` are shown, even when they are excluded in
the ModelForm.
b. `MessageForm.field_order` has no effect when used in an admin view.
2. When a model field has `through`, it is not shown, as it should be an
inline. Although it will be added to the fields again in the form
(`MessageForm.overruled_model_m2m_field`)
a. This makes it appear "randomly" in the ordering as it is updated to
the end of base_fields (django.forms.models:324)

**Expected behavior:**
1. `MessageForm` takes precedence over `MessageAdmin`.
a. Excluded fields are not shown
b. `ModelForm.Meta.fields` and `ModelForm.field_order` are used in favor
of `ModelAdmin.get_fields()`
2. a. Fields with a through that are also specified in the form itself are
ordered correctly according to 1b.
--
Ticket URL: <https://code.djangoproject.com/ticket/35696>
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[Django]

#35696: ModelAdmin is overruling the fields of ModelForm
-------------------------------+--------------------------------------

Reporter: Jurrian Tromp | Owner: (none)

Type: Bug | Status: new
Component: Forms | Version: 4.2

Severity: Normal | Resolution:

Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------+--------------------------------------

Description changed by Jurrian Tromp:

Old description:

New description:

There are workarounds to get both the field order and readonly fields
right, which comes down to defining `MessageAdmin.get_fields()` and/or
`MessageAdmin.get_readonly_fields()`, to take full control. However, IMHO
this should not be the default.

--
--
Ticket URL: <https://code.djangoproject.com/ticket/35696#comment:1>

[Django]

#35696: ModelAdmin is overruling the fields of ModelForm
-------------------------------+--------------------------------------
Reporter: Jurrian Tromp | Owner: (none)

Type: Bug | Status: closed
Component: Forms | Version: 4.2
Severity: Normal | Resolution: invalid

Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------+--------------------------------------

Changes (by Carlton Gibson):

* resolution: => invalid
* status: new => closed

Comment:

This is the expected behaviour as far as I can see. The
[https://docs.djangoproject.com/en/5.1/ref/contrib/admin/#django.contrib.admin.ModelAdmin.form
ModelAdmin.form docs] state that the `fields` meta option is ignored on
any provided form. (The provided form class is used as the base, but
fields are derived from the admin options `fields`/`fieldsets`.)

If you want to bypass the form generation you should override
`get_form()`.

I'd suggest following up in TicketClosingReasons/UseSupportChannels if you
need to dig further.
--
Ticket URL: <https://code.djangoproject.com/ticket/35696#comment:2>