What are the best practices for using clean methods in Django models?

What are the best practices for using clean methods in Django models?

When using clean methods in Django models, it's important to ensure that you validate data effectively. Here are some best practices:

1. Use the clean() method for model-wide validation.
2. Implement field-specific validation in the clean_<fieldname>() methods.
3. Keep validation logic separate from business logic.
4. Raise ValidationError for any invalid data.
5. Test your clean methods thoroughly.

Can you give an example of a clean method in a Django model?

Sure! Here's a simple example:

from django.core.exceptions import ValidationError
from django.db import models

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=10, decimal_places=2)

    def clean(self):
        if self.price < 0:
            raise ValidationError('Price cannot be negative.')

What should I do if I have multiple fields to validate?

You can still use the clean() method to validate multiple fields together. For example:

def clean(self):
    if self.start_date > self.end_date:
        raise ValidationError('Start date must be before end date.')

Are there any performance considerations I should keep in mind?

Yes, be mindful of performance when validating large datasets. Avoid complex queries in the clean() method, and consider using database constraints for critical validations.