from django.db import models

class Article(models.Model):
    title = models.CharField(max_length=200)
    slug = models.SlugField(null=True, blank=True)
    published = models.BooleanField(default=False)
    
    class Meta:
        constraints = [
            models.UniqueConstraint(
                fields=['slug'],
                condition=models.Q(published=True),
                name='unique_published_slug'
            )
        ]

pip install -U djangorestframework