Django forms, inheritance and order of form fields

user_109070 0
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I'm using Django forms in my website and would like to control the order of the fields.

Here's how I define my forms:

class edit_form(forms.Form):
    summary = forms.CharField()
    description = forms.CharField(widget=forms.TextArea)


class create_form(edit_form):
    name = forms.CharField()

The name is immutable and should only be listed when the entity is created. I use inheritance to add consistency and DRY principles. What happens which is not erroneous, in fact totally expected, is that the name field is listed last in the view/html but I'd like the name field to be on top of summary and description. I do realize that I could easily fix it by copying summary and description into create_form and loose the inheritance but I'd like to know if this is possible.

Why? Imagine you've got 100 fields in edit_form and have to add 10 fields on the top in create_form - copying and maintaining the two forms wouldn't look so sexy then. (This is not my case, I'm just making up an example)

So, how can I override this behavior?

Edit:

Apparently there's no proper way to do this without going through nasty hacks (fiddling with .field attribute). The .field attribute is a SortedDict (one of Django's internal datastructures) which doesn't provide any way to reorder key:value pairs. It does how-ever provide a way to insert items at a given index but that would move the items from the class members and into the constructor. This method would work, but make the code less readable. The only other way I see fit is to modify the framework itself which is less-than-optimal in most situations.

In short the code would become something like this:

class edit_form(forms.Form):
    summary = forms.CharField()
    description = forms.CharField(widget=forms.TextArea)


class create_form(edit_form):
    def __init__(self,*args,**kwargs):
        forms.Form.__init__(self,*args,**kwargs)

        self.fields.insert(0,'name',forms.CharField())

That shut me up :)

django-forms django python
11 Answers

From Django 1.9+

Django 1.9 adds a new Form attribute, field_order, allowing to order the field regardless their order of declaration in the class.

class MyForm(forms.Form):
    summary = forms.CharField()
    description = forms.CharField(widget=forms.TextArea)
    author = forms.CharField()
    notes = form.CharField()

    field_order = ['author', 'summary']

Missing fields in field_order keep their order in the class and are appended after the ones specified in the list. The example above will produce the fields in this order: ['author', 'summary', 'description', 'notes']

See the documentation: https://docs.djangoproject.com/en/stable/ref/forms/api/#notes-on-field-ordering

Up to Django 1.6

I had this same problem and I found another technique for reordering fields in the Django CookBook:

class EditForm(forms.Form):
    summary = forms.CharField()
    description = forms.CharField(widget=forms.TextArea)


class CreateForm(EditForm):
    name = forms.CharField()

    def __init__(self, *args, **kwargs):
        super(CreateForm, self).__init__(*args, **kwargs)
        self.fields.keyOrder = ['name', 'summary', 'description']
user_1389280

See the notes in this SO question on the way Django's internals keep track of field order; the answers include suggestions on how to "reorder" fields to your liking (in the end it boils down to messing with the .fields attribute).

user_958100

The above answers are right but incomplete. They only work if all the fields are defined as class variables. What about dynamic form fields which have to be defined in the intitialiser (__init__)?

from django import forms

class MyForm(forms.Form):
    field1 = ...
    field2 = ...

    field_order = ['val', 'field1', 'field2']

    def __init__(self, val_list, *args, **kwargs):
        super(MyForm, self).__init__(*args, **kwargs)
        vals = zip(val_list, val_list)
        self.fields['val'] = forms.CharField(choices=vals)

The above will never work for val but will work for field1 and field2 (if we reorder them). You might want to try defining field_order in the initialiser:

class MyForm(forms.Form):
    # other fields

    def __init__(self, val_list, *args, **kwargs):
        super(MyForm, self).__init__(*args, **kwargs)
        vals = zip(val_list, val_list)
        self.fields['val'] = forms.CharField(choices=vals)
        self.field_order = ['val', 'field1', 'field2']

but this will also fail because the field order is fixed before the call to super().

Therefore the only solution is the constructor (__new__) and set field_order to a class variable.

class MyForm(forms.Form):
    # other fields

    field_order = ['val', 'field1', 'field2']

    def __new__(cls, val_list, *args, **kwargs):
        form = super(MyForm, cls).__new__(cls)
        vals = zip(val_list, val_list)
        form.base_fields['val'] = forms.CharField(choices=vals)
        return form
user_7506700
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