Why is a Django model taking so long to load in admin?

Question

I have a fairly simple Django set up for a forum, and one of the most basic models is this, for each thread:

class Post(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    last_reply = models.DateTimeField(auto_now_add=True, blank=True, null=True)
    username = models.ForeignKey(User, related_name="forumuser")

    fixed = models.BooleanField(_("Sticky"), default=False)
    closed = models.BooleanField(default=False)
    markdown_enabled = models.BooleanField(default=False)

    reply_count = models.IntegerField(default=0)
    title = models.CharField(_("Title Post"), max_length=255)
    content = models.TextField(_("Content"), blank=False)
    rating = models.IntegerField(default=0)
    followers = models.IntegerField(default=0)

    ip_address = models.CharField(max_length=255)

    def __unicode__(self):
        return self.title

    def get_absolute_url(self):
        return "/post/%s/" % self.id

Then we have some replies:

class PostReply(models.Model):
    user = models.ForeignKey(User, related_name='replyuser')
    post = models.ForeignKey(Post, related_name='replypost')
    created = models.DateTimeField(auto_now_add=True)
    content = models.TextField()
    ip_address = models.CharField(max_length=255)
    quoted_post = models.ForeignKey('self', related_name='quotedreply', blank=True, null=True)
    rating = models.IntegerField(default=0)
    reply_order = models.IntegerField(default=1)

Now, currently there just over 1600 users, 6000 Posts, and 330,000 PostReply objects in the db for this setup. When I run this SQL query:

 SELECT * FROM `forum_post` LIMIT 10000

I see that Query took 0.0241 sec which is fine. When I browse to the Django admin section of my site, pulling up an individual Post is rapid, as is the paginated list of Posts.

However, if I try and pull up an individual PostReply, it takes around 2-3 minutes to load.

Obviously each PostReply admin page will have a dropdown list of all the Posts in it, but can anyone tell me why this or anything else would cause such a dramatically slow query? It's worth noting that the forum itself is pretty fast.

Also, if it is something to do with that dropdown list, has anyone got any suggestions for making that more usable?

Answer 1

Try to add all foreign keys in raw_id_fields in admin

class PostReplyAdmin(ModelAdmin):
     raw_id_fields = ['user', 'post', 'quoted_post']

This will decrease page's load time in change view. The problem is that django loads ForeignModel.objects.all() for each foreign key's dropdowns.