Django Model Meta Options with Custom Manager Chaining

Snippet

Django Model Meta Options with Custom Manager Chaining

This snippet showcases Django's powerful Model Meta options and custom manager chaining. The Article model implements a layered manager approach where PublishedManager extends ActiveManager, creating a chain of filtered querysets. The Meta class defines composite indexes for performance, database-level constraints for data integrity, and default ordering. Custom classmethods provide user-specific visibility logic.

snippet.py
python
from django.db import models
from django.db.models import Q
from django.utils import timezone
 
class ActiveManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(is_active=True)
 
class PublishedManager(ActiveManager):
    def get_queryset(self):
        return super().get_queryset().filter(
            Q(published_at__isnull=True) | Q(published_at__lte=timezone.now())
        )
 
class Article(models.Model):
    title = models.CharField(max_length=200)
    slug = models.SlugField(unique=True)
    content = models.TextField()
    is_active = models.BooleanField(default=True)
    published_at = models.DateTimeField(null=True, blank=True)
    author = models.ForeignKey('auth.User', on_delete=models.CASCADE)
    created_at = models.DateTimeField(auto_now_add=True)
 
    objects = models.Manager()
    active = ActiveManager()
    published = PublishedManager()
 
    class Meta:
        indexes = [
            models.Index(fields=['slug']),
            models.Index(fields=['-published_at', 'is_active']),
        ]
        constraints = [
            models.UniqueConstraint(
                fields=['author', 'slug'],
                name='unique_author_slug'
            )
        ]
        ordering = ['-created_at']
        verbose_name = 'Article'
        verbose_name_plural = 'Articles'
 
    def __str__(self):
        return self.title
 
    @classmethod
    def get_visible_for_user(cls, user):
        if user.is_staff:
            return cls.objects.all()
        return cls.published.all()

django

Breakdown

class ActiveManager(models.Manager):

Create custom manager that filters for active records, reusable across multiple models

objects = models.Manager(); active = ActiveManager(); published = PublishedManager()

Assign multiple manager instances to the model enabling different query perspectives simultaneously

models.Index(fields=['-published_at', 'is_active'])

Define composite index with descending order for efficient chronological queries with status filtering

models.UniqueConstraint(fields=['author', 'slug'])

Add database-level constraint ensuring author-slug combination uniqueness at the database level

@classmethod def get_visible_for_user(cls, user):

Create classmethod that returns appropriate queryset based on user permissions for visibility logic

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Django Model Meta Options with Custom Manager Chaining

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