python - Django admin: exclude field on change form only

Question

If there a way to detect if information in a model is being added or changed.

If there is can this information be used to exclude fields.

Some pseudocode to illustrate what I'm talking about.

class SubSectionAdmin(admin.ModelAdmin):
    if something.change_or_add = 'change':
        exclude = ('field',)
    ...

Thanks

Answer 1

orwellian's answer will make the whole SubSectionAdmin singleton change its exclude property.

A way to ensure that fields are excluded on a per-request basis is to do something like:

class SubSectionAdmin(admin.ModelAdmin):
    # ...
    def get_form(self, request, obj=None, **kwargs):
        """Override the get_form and extend the 'exclude' keyword arg"""
        if obj:
            kwargs.update({
                'exclude': getattr(kwargs, 'exclude', tuple()) + ('field',),
            })
        return super(SubSectionAdmin, self).get_form(request, obj, **kwargs)

which will just inform the Form to exclude those extra fields.

Not sure how this will behave given a required field being excluded...