Django model managers for custom querysets

                  from django.db import models
from django.utils import timezone


class PostQuerySet(models.QuerySet):
    def published(self):
        return self.filter(
            status='published',
            published_at__lte=timezone.now()
        )

    def by_author(self, author):
        return self.filter(author=author)


class PostManager(models.Manager):
    def get_queryset(self):
        return PostQuerySet(self.model, using=self._db)

    def published(self):
        return self.get_queryset().published()


class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    author = models.ForeignKey('auth.User', on_delete=models.CASCADE)
    status = models.CharField(
        max_length=20,
        choices=[('draft', 'Draft'), ('published', 'Published')]
    )
    published_at = models.DateTimeField(null=True, blank=True)

    objects = PostManager()

    def __str__(self):
        return self.title