Django ModelForm inheritance and Meta inheritance

Question

I have this ModelForm:

class Event(forms.ModelForm):

    def __init__(self, *args, **kwargs):
        super(Event, self).__init__(*args, **kwargs)
        ##Here make some changes such as:
        self.helper = FormHelper()
        self.helper.form_method = 'POST'
        ##Many settings here which **i don't want to rewrite in 10 child classes**

    class Meta:
        model = Event
        exclude = something...
        widgets = some settings here also.

And this child ModelForm:

class UpgradedEvent(Event):

    def __init__(self, *args, **kwargs):
        super(UpgradedEvent,self).__init__(*args,**kwargs)

    class Meta(Event.Meta):
        model = UpgradedEvent

UpgradedEvent is a child of Event model but has some extra fields. How can i inherit all the settings from the Event FORM into UpgradedEvent FORM?

When running the above code, it renders the Event form. Is there a way to inherit only the settings inside __init__ ?

EDIT

Check out the answer, it works great but keep in mind: you need to create another instance of FormHelper in your child class, otherwise it won't work. So child class should look something like:

class UpgradedEvent(Event):

    def __init__(self, *args, **kwargs):
        super(UpgradedEvent,self).__init__(*args,**kwargs)
        self.helper = FormHelper()

    class Meta(Event.Meta):
        model = UpgradedEvent

willeM_ Van Onsem · Accepted Answer · 2018-05-23 11:41:10Z

You can obtain the fields the Meta above, and extend the lists, etc.:

class UpgradedEventForm(EventForm):

    def __init__(self, *args, **kwargs):
        super(UpgradedEventForm,self).__init__(*args,**kwargs)
        # some extra settings
        # ...
        # for example
        self.fields['extra_field'].initial = 'initial value of extra field'

    class Meta(EventForm.Meta):
        model = UpgradedEvent
        exclude = EventForm.Meta.exclude + ['extra_exclude1', 'extra_exclude2']
        fields = EventForm.Meta.fields + ['extra_field']

So by using inheritance, we can add extra procedures to the __init__ function by performing some extra actions after the super(UpgradedEventForm, self) call, and wwe can access the attributes of our parent, and extend these.

Note that you better name your forms with a Form suffix, since now your models clash with your forms. As a result, your Form seems to have as model a reference to the Form itself. By using proper "nomenclature", you avoid a lot of mistakes.

Sardorbek Imomaliev · Accepted Answer · 2018-05-23 11:59:00Z

7

Create FormWithSettings which will hold common settings for you form classes and inherit it

class FormWithSettings(forms.ModelForm):

    def __init__(self, *args, **kwargs):
        super(FormWithSettings, self).__init__(*args, **kwargs)
        ##Here make some changes such as:
        self.helper = FormHelper()
        self.helper.form_method = 'POST'
        ##Many settings here which **i don't want to rewrite in 10 child classes**

    class Meta:
        exclude = something...
        widgets = some settings here also.

class EventForm(FormWithSettings):

    def __init__(self, *args, **kwargs):
        super(EventForm, self).__init__(*args,**kwargs)

    class Meta(FormWithSettings.Meta):
        model = Event

class UpgradedEventForm(FormWithSettings):

    def __init__(self, *args, **kwargs):
        super(UpgradedEventForm, self).__init__(*args,**kwargs)

    class Meta(FormWithSettings.Meta):
        model = UpgradedEvent

edited May 23, 2018 at 11:59

answered May 23, 2018 at 11:35

Sardorbek Imomaliev

15.6k3 gold badges55 silver badges69 bronze badges

6 Comments

Mike Vlad Over a year ago

The thing is i have many settings in __init__ which i don't want to copy-paste in 10 child classes of Event Form.

Mike Vlad Over a year ago

I did try to implement this idea and i have absolutely no idea why it's not working. If i inherit the meta, it works, if i try UpgradedEventForm(FormWithSettings) i lose the extra fields from the Upgraded class and i have absolutely no idea why since they work fine if i just inherit the meta.

Sardorbek Imomaliev Over a year ago

@MikeVlad post your actual code please, and what you expect of it

Mike Vlad Over a year ago

@i figured out, i ll edit the question. it was that i had to create another instance of FormHelper - Crispy Forms

Aseem Over a year ago

I had to restart the django server to see changes

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