===================
Forms
===================

request.POST binding to wrong parameter in forms
---------------------------------------------------

This is a common idiom in a view.::

    def view_func(request):
        form = FormClass()
        if request.method == 'POST':
            form=FormClass(request.POST)#Gotcha
            ....
        payload = {'form':form}
        return render_to_response(...)
        
Now suppose we edited our form class to::

    class FormClass(forms.Form):
        def __init__(self, user = None, *args, **kwargs):
            ...
            
request.POST will bind to user, when we meant to be the POST data.

Solution:

Rewrite the gotcha line as
    
    form=FormClass(data=request.POST)
    

Using form.cleaned_data before calling form.is_valid
-------------------------------------------------------

Even if you are sure your form passes validation, you still need to call
`is_valid`. `form.cleaned_data` is calculated after `form.is_valid` is called,
which you probably are using in your `form.save()`.

Overriding form.save in ModelForms:
-----------------------------------------
Similar to `models.save`, forms.save are often (wrongly) overriden as `forms.save`::

    def forms.save(self):
        ...
        super(FormCLass, self).save()

This won't work in many cases, for example `form.save(commit=False)`

Solution:

Always save as::

    def forms.save(self, *args, **kwargs):
        ...
        super(FormClass, self).save(*args, **kwargs)


Not calling superclass __init__
---------------------------------

You might want to change the widget of a particular form field and this can be
done by overriding Form's __init__.::

    from django.contrib.admin.widgets import AdminFileWidget

    class FormClass(forms.ModelForm):

        class Meta:
            model = Profile

        def __init__(self, *args, **kwargs):
            self.fields['picture'].widget = AdminFilewidget() #Gotcha

self.fields is populated after __init__ of ModelForm has executed. So, make sure to call superclass __init__ before accessing self.fields.::

        def __init__(self, *args, **kwargs):
            super(FormClass, self).__init__(*args, **kwargs)
            self.fields['picture'].widget = AdminFilewidget()