Dynamic fields in Django Admin

Question

I want to have additional fields regarding value of one field. Therefor I build a custom admin form to add some new fields.

Related to the blogpost of jacobian 1 thi

Answer 1

While Jacob's post might work all right for regular ModelForms (even though it's more than a year and a half old), the admin is a somewhat different matter.

All the declarative way of defining models, forms ModelAdmins and whatnot makes heavy use of metaclasses and class introspection. Same with the admin – when you tell a ModelAdmin to use a specific form istead of creating a default one, it introspects the class. It gets the list of fields and other stuff from the class itself without instantiating it.

Your custom class, however, does not define the extra form field at class level, instead it dynamically adds one after it has been instantiated – that's too late for the ModelAdmin to recognize this change.

One way to go about your problem might be to subclass ModelAdmin and override its get_fieldsets method to actually instantiate the ModelForm class and get the list of fields from the instance instead of the class. You'll have to keep in mind, though, that this might be somewhat slower than the default implementation.