Django Formsets

Django Formsets

What: Multiple instances of the same form on one page (e.g. many products in one order). Same form, N times, one submit.

• formset_factory(Form, extra=2, max_num=10) — plain forms, no model.
• modelformset_factory(Model, fields=…, extra=…, can_delete=True) — tied to model, can save/update/delete.
• inlineformset_factory(Parent, Child, fields=…) — for related objects (e.g. Order + OrderItems). Pass instance=order in the view.

Template must have: `` (TOTAL_FORMS, INITIAL_FORMS, etc.). Without it, formset breaks.

View pattern:
POST → formset = FormSet(request.POST, request.FILES) (and for inline: instance=parent).
GET → formset = FormSet() or FormSet(queryset=...) for existing data.
If valid: loop for form in formset and only save when form.cleaned_data (and not form.cleaned_data.get('DELETE') for model formsets with delete).

Gotchas:

• Check form.cleaned_data before saving — empty rows still appear in the formset.
• File uploads: pass request.FILES into the formset.
• Dynamic add/remove: update id_form-TOTAL_FORMS in the management form and renumber indices when adding rows in JS.

Custom validation: subclass BaseFormSet, override clean(), call super().clean(), then add your checks (e.g. at least one row, no duplicate names).

Use model formset when you’re editing DB rows; inline when editing parent + children together; plain formset when it’s just a bunch of forms not tied to one model.