Filtering the Aggregate in the Django ORM

Question

I have a function that looks like this:

def post_count(self):
        return self.thread_set.aggregate(num_posts=Count(\'post\'))[\'num_posts\']

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Answer 1

Would it be ok to change around things a bit?

As illustrated below, you could add a post_count property to the Thread class, which counts active Posts in a Thread.

This post_count could then be used to calculate active posts in a category by adding up all active posts in all thread in a category.

class Category(models.Model):
    name = models.CharField(max_length=100)
    slug = models.SlugField(max_length=100, blank=True, primary_key=True)
    ordering = models.IntegerField(max_length=3, default=0)

    @property
    def thread_count(self):
        return self.thread_set.all().count()

    @property
    def post_count(self): # <-- Changed
        return reduce(lambda x,y: x + y, [x.post_count for x in self.thread_set.all()])

class Thread(models.Model):
    user = models.ForeignKey(User)
    category = models.ForeignKey(Category)
    title = models.CharField(max_length=100)
    slug = models.SlugField(max_length=100)
    content = models.TextField()
    created = models.DateTimeField(auto_now_add=True)
    latest_activity = models.DateTimeField(auto_now_add=True)

    @property
    def post_count(self): # <---- Newly added
        return self.post_set.filter(status = 'ACTIVE').count()

class Post(models.Model):
    thread = models.ForeignKey(Thread)
    parent = models.ForeignKey('Post', null=True, blank=True)
    display_name = models.CharField(max_length=100)
    email = models.EmailField(db_index=True)
    ip_address = models.IPAddressField(null=True, blank=True)
    content = models.TextField()
    status = models.CharField(choices=STATUS_CHOICES, max_length=25, db_index=True, default='approved')
    created = models.DateTimeField()