#30407: Modelform initial values override instance values when both are set
-----------------------------+--------------------------------------
Reporter: Alper Cugun | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 2.2
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Description changed by Alper Cugun:
Old description:
> We ran into a bug (on our side) where our data was not being displayed in
> a ModelForm for existing instance because we were setting both initial
> values as the instance in the ModelForm.
>
> Digging into the documentation it turns out that for [ModelForm initial
> overrides instance values
> https://docs.djangoproject.com/en/2.2/topics/forms/modelforms/#providing-
> initial-values] ("Initial values provided this way will override both
> initial values from the form field and values from an attached model
> instance.") whereas for [normal Forms initial
> https://docs.djangoproject.com/en/2.2/ref/forms/api/#dynamic-initial-
> values] does not take precedence over bound data ("These values are only
> displayed for unbound forms, and they’re not used as fallback values if a
> particular value isn’t provided."). Maybe that's my mistake for thinking
> a bound Form and a ModelForm with an instance are roughly equivalent.
>
> I tracked this down to [this commit
> https://github.com/django/django/commit/51dc4ecf943d1dcc044ed956925760f9d480f56c]
> 12 years ago and it seems that nobody has complained much about this
> piece of code in the mean time. So maybe it isn't a problem but I think
> there is something to be said for reversing the precedence in ModelForm.
>
> I've attached a draft diff to fix this.
New description:
We ran into a bug (on our side) where our data was not being displayed in
a ModelForm for existing instance because we were setting both initial
values as the instance in the ModelForm.
Digging into the documentation it turns out that for [ModelForm
https://docs.djangoproject.com/en/2.2/topics/forms/modelforms/#providing-
initial-values] initial overrides instance values ("Initial values
provided this way will override both initial values from the form field
and values from an attached model instance.") whereas for normal [Forms
https://docs.djangoproject.com/en/2.2/ref/forms/api/#dynamic-initial-
values] initial does not take precedence over bound data ("These values
are only displayed for unbound forms, and they’re not used as fallback
values if a particular value isn’t provided."). Maybe that's my mistake
for thinking a bound Form and a ModelForm with an instance are roughly
equivalent.
I tracked this down to [this commit
https://github.com/django/django/commit/51dc4ecf943d1dcc044ed956925760f9d480f56c]
12 years ago and it seems that nobody has complained much about this piece
of code in the mean time. So maybe it isn't a problem but I think there is
something to be said for reversing the precedence in ModelForm.
I've attached a draft diff to fix this.
--
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Ticket URL: <https://code.djangoproject.com/ticket/30407#comment:1>
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