Re: FormSet issue. Pre-populating from queryset

[maeck]

Malcolm,

Thanks for the comment.
I truly understand where this is coming from. This issue is completely
my issue of taking things for granted.
I have been coding around in Django for a while now (hooked on in the
0.95 days), and have been coding most of the form stuff (including
inlines) all by hand.
When I noticed the Formset class, I tried to make it work in the wrong
place.
Brian pointed me to the inlineformsets documentation and I have not
been happier.
It really is easy now to build forms with inlines.

This stuff has come a long way, and life will be much easier than it
was before.

Thanks for Django,

Maeck
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Re: FormSet issue. Pre-populating from queryset

[Malcolm Tredinnick]

On Thu, 2008-12-11 at 20:55 -0800, maeck wrote:
[...]
> Now I can pass the fieldnames as values('parent') for now, It would be
> easier if initial did not care if the _id is provided or not.
> Or am I missing something else?

What you're missing, or rather, assuming, is that querysets are ideal or
intended to be used directly as initial data, and that isn't the case.
Forms are separate pieces of code from models and shouldn't have to
understand all the foibles of models (i.e. enforce loose coupling). If
you want to pass in the results of a queryset directly, it's easy, but
you do have to take care and pass in the right values by specifying the
names of the fields. You know the models you are using, so writing down
their field names isn't particularly onerous.

It happens that values(), by default, returns "parent_id" for historical
reasons. However, we set things up so that you an also ask it to return
"parent" by specifying that in the fields list. So use that
functionality.

If you still think that's all just nit-picking and we should compromise
to avoid the inconvenience, realise how bad it is: first you have to
teach Form's initial data that when they expect "foo", it might really
be spelt "foo_id". The form doesn't know this is a foreign key, it just
knows it's a choice field. But since "_id" isn't the only possible
suffix, now the form has to be able to handle any possible suffix --
"foo_blah", for example -- since the database column name can be
specified in the model. So we're looking at all sorts of possible
alternate names for the key. Thus, the form really needs to have
reference to the full model to inspect all that. Now we're passing in
models and tying the form to the model and it's starting to look like
you really should be using ModelFormSet. Short version: it's just not
worth all the complexity. We have ModelFormSets for standard model->
form conversions and an easy way to produce sequences of dictionaries if
you have other situations where a FormSet is more useful.

These things have a way of being much more complicated than they look on
the surface. :-)

Regards,
Malcolm


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Re: FormSet issue. Pre-populating from queryset

[Brian Rosner]

On Thu, Dec 11, 2008 at 9:55 PM, maeck  wrote:
> Now I can pass the fieldnames as values('parent') for now, It would be
> easier if initial did not care if the _id is provided or not.
> Or am I missing something else?

You shouldn't be using a regular formset. Django provides model
formsets that know how to deal with this internally. Go read up on
inline formsets which is a layer on top of model formsets.

http://docs.djangoproject.com/en/dev/topics/forms/modelforms/#inline-formsets

-- 
Brian Rosner
http://oebfare.com

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Re: FormSet issue. Pre-populating from queryset

[maeck]

Thanks Malcolm,

Just figured out the values transformation on querysets myself.
Nevertheless, in my experience there seems to be an issue with
foreignkeys when using queryset values in combination with formsets.
Values returns keys like 'parent_id', however formsets expect the
fieldname as 'parent'.
(I am using Django 1.0.2)

Now I can pass the fieldnames as values('parent') for now, It would be
easier if initial did not care if the _id is provided or not.
Or am I missing something else?

Maeck


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Re: FormSet issue. Pre-populating from queryset

[Malcolm Tredinnick]

On Thu, 2008-12-11 at 20:19 -0800, maeck wrote:
> The example below is a snippet from a view where I use a form to show
> 'Parent' and a formset to show its 'Children'.
> If I get the children as a queryset and pass it on to the formsets
> initial property, it errors out with: 'Parent' object is not iterable
> 
> InlineFormSet   = formset_factory(InlineForm)
> data  = Parent.objects.get(id = data_id)
> form  = ParentForm(instance=data)
> inlinedata= Child.objects.filter(parent_id  = data_id)
> inlineform= InlineChildFormSet(initial=inlinedata)

Initial for data should be a something that is, or at least behaves
like, a sequence of dictionaries. A queryset is behaves like a sequence,
but the elements of that sequence don't behave like dictionaries
(they're objects -- in this case, Parent objects).

So whilst, "for key in obj:" works when "obj" is a dictionary, it
doesn't work when "obj" is a Django Model subclass (e.g. a Parent).

Since the requirement is to pass in a list of dictionaries, using the
values() method on your inlinedata call will get you a long way there.

Regards,
Malcolm



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