Snippet

Django ModelForm Custom Validation with clean()

The clean() method validates across multiple fields. It raises ValidationError for invalid combinations. This runs after field-specific clean methods and enables complex business rule validation.

snippet.py

python

from django import forms
from .models import Product
 
class ProductForm(forms.ModelForm):
    class Meta:
        model = Product
        fields = ['name', 'price', 'stock']
 
    
    def clean(self):
        cleaned_data = super().clean()
        price = cleaned_data.get('price')
        stock = cleaned_data.get('stock')
        if price and price < 0:
            raise forms.ValidationError('Price cannot be negative')
        if stock is not None and stock < 0:
            raise forms.ValidationError('Stock cannot be negative')
        if price and stock and price * stock > 1000000:
            raise forms.ValidationError('Inventory value exceeds limit')
        return cleaned_data

django

Breakdown

def clean(self)

Override to implement cross-field validation logic

raise forms.ValidationError()

Django's standard way to signal validation failures

price * stock > 1000000

Example of business rule validation across related fields

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Django ModelForm Custom Validation with clean()

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