[Fixed]-Django admin validation for inline form which rely on the total of a field between all forms


I know the question was asked a long time ago, but since I struggled with the same problem, I think it might be usefull.

The key here is to define a custom formset to embed into the tabular admin form, then to override the formset clean’s method.

Here’s an example : a composition is made of composition_elements, each composition_element has a percent field, and I want to validate that the total percent is equal to 100.

from django import forms
from django.forms.models import BaseInlineFormSet
from django.core.exceptions import ValidationError
from django.utils.translation import ugettext_lazy as _
from django.contrib import admin
from .models import Composition, CompositionElement

class CompositionElementFormSet(BaseInlineFormSet):
    Validate formset data here
    def clean(self):
        super(CompositionElementFormSet, self).clean()

        percent = 0
        for form in self.forms:
            if not hasattr(form, 'cleaned_data'):
            data = form.cleaned_data
            percent += data.get('percent', 0)

        if percent != 100:
            raise ValidationError(_('Total of elements must be 100%%. Current : %(percent).2f%%') % {'percent': percent})

class CompositionElementAdmin(admin.TabularInline):
    model = CompositionElement
    formset = CompositionElementFormSet

class CompositionAdmin(admin.ModelAdmin):
    inlines = (CompositionElementAdmin,)

admin.site.register(Composition, CompositionAdmin)

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