The Error "Models aren't loaded yet" keeps bugging me!

Using Django
1

I have some code being written where I have tried to automate adding and deleting model objects as I have shown below in my models.py:

from django.db import models
from django.contrib.auth.models import User
from django.db.models.signals import post_save, post_delete
from django.dispatch import Signal
from django.db.models import Max, Count
from django.apps import apps

# Create your models here.
class Player(models.Model):
    player_name = models.CharField(max_length=150)
    current_level_no = models.IntegerField(null=True)
    no_of_moves = models.IntegerField(null=True)    

    class Meta:
        verbose_name_plural = 'Players'

    def __str__(self):
        return self.player_name

class PlayerStats(models.Model):
    player_name = models.ForeignKey(to=Player, on_delete=models.CASCADE)
    level_no = models.IntegerField(null=True)
    moves = models.IntegerField(null=True)

    class Meta:
        verbose_name_plural = 'Players Stats'

# It works!
TotalLevels = 15

MaxCurrentLevel = PlayerStats.objects.aggregate(max_levels=Max('level_no'))['max_levels']
PlayerCount = Player.objects.aggregate(count_players=Count('player_name', distinct=True))['count_players']


def create_player(sender, instance, created, **kwargs):
    if created:
        new_username=instance.username
        Player.objects.create(player_name=new_username, current_level_no=None, no_of_moves=None)

def delete_player(sender, instance, **kwargs):
    deleted_username=instance.username
    Player.objects.filter(player_name=deleted_username).delete()

def create_player_stat(sender, instance, **kwargs):
    for x in range(1, TotalLevels+1):
        PlayerStats.objects.create(player_name=instance, level_no=x, moves=None)

if MaxCurrentLevel != TotalLevels and PlayerCount != 0:
    if MaxCurrentLevel < TotalLevels:
        for x in Player.objects.all().values_list('player_name', flat=True):
            instance = Player.objects.get(player_name=x)
            for y in range(TotalLevels-MaxCurrentLevel, TotalLevels+1):
                PlayerStats.objects.create(player_name=instance, level_no=y, moves=None)
    else:
            for y in range(MaxCurrentLevel-TotalLevels, MaxCurrentLevel+1):
                b = PlayerStats.objects.filter(level_no=y, moves=None)
                print(b)
                b.delete()

post_save.connect(create_player, sender=User)
post_delete.connect(delete_player, sender=User)

post_save.connect(create_player_stat, sender=Player)

What I have done is make sure that there are only as many Foreign Key model objects of PlayerStats associated with each Player(kinda like Primary key in this case) of the Player Model and that number is governed by the Total levels number. So if there are more or less levels associated with each player in PlayerStats Model than the Total levels value, I made a conditional piece of code with a couple of loops to accordingly delete or add the Model objects.

The problem really is that the creation part works fine when I need more levels and increase Total Levels. But when I decrease it, that is delete the extra, I get an error: “Models aren’t loaded yet”.
Here is the full error if you need it:

C:\Users\Prithvi\Desktop\Prithvi\PROJECTS\Rahul stuff\bloxnsims\website>python manage.py runserver
<QuerySet [<PlayerStats: PlayerStats object (70)>, <PlayerStats: PlayerStats object (86)>, <PlayerStats: PlayerStats object (104)>]>
<QuerySet [<PlayerStats: PlayerStats object (70)>, <PlayerStats: PlayerStats object (86)>, <PlayerStats: PlayerStats object (104)>]>
Watching for file changes with StatReloader
Exception in thread django-main-thread:
Traceback (most recent call last):
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\threading.py", line 916, in _bootstrap_inner
    self.run()
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\utils\autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\management\commands\runserver.py", line 109, in inner_run
    autoreload.raise_last_exception()
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\utils\autoreload.py", line 77, in raise_last_exception
    raise _exception[1]
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\management\__init__.py", line 337, in execute    
    autoreload.check_errors(django.setup)()
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\utils\autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\apps\registry.py", line 114, in populate
    app_config.import_models()
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\apps\config.py", line 211, in import_models
    self.models_module = import_module(models_module_name)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\importlib\__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "C:\Users\Prithvi\Desktop\Prithvi\PROJECTS\Rahul stuff\bloxnsims\website\bloxors\models.py", line 79, in <module>
    b.delete()
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\query.py", line 710, in delete
    collector.collect(del_query)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\deletion.py", line 188, in collect
    if self.can_fast_delete(objs):
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\deletion.py", line 150, in can_fast_delete  
    for related in get_candidate_relations_to_delete(opts)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\deletion.py", line 58, in get_candidate_relations_to_delete
    f for f in opts.get_fields(include_hidden=True)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\options.py", line 734, in get_fields        
    return self._get_fields(include_parents=include_parents, include_hidden=include_hidden)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\options.py", line 794, in _get_fields       
    all_fields = self._relation_tree
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\utils\functional.py", line 80, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\options.py", line 707, in _relation_tree    
    return self._populate_directed_relation_graph()
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\options.py", line 678, in _populate_directed_relation_graph
    all_models = self.apps.get_models(include_auto_created=True)
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\apps\registry.py", line 178, in get_models
    self.check_models_ready()
  File "C:\Users\Prithvi\AppData\Local\Programs\Python\Python36\lib\site-packages\django\apps\registry.py", line 140, in check_models_ready    
    raise AppRegistryNotReady("Models aren't loaded yet.")
django.core.exceptions.AppRegistryNotReady: Models aren't loaded yet.

What utterly made me go mad about this is that this error is so vague and I have had it come up a bunch of times. I have had to scratch ideas I have had in mind and start fresh to get done what I want, always with fear about if my new method or approach will also become an error! All I get to know is that I need to do something else and that my current method/approach is a dead-end! I am sorry if this is a little ranty, but I have been pulling my hair out about this so much to the point that if I keep this up, I might actually go bald in a year!

I am clearly not as well-versed with django as much as you all are and as a fellow django user, I request your help on this issue. I am greatful for whatever help I get!

2

Django needs to load all of the apps before you can work with them. So adding code which queries the database below your model definitions throws this error. For more details, check out https://docs.djangoproject.com/en/2.2/ref/applications/#how-applications-are-loaded

Thankfully, the fix is to move the non-model code into a ready() method so that the code is ran immediately after Django has loaded everything into memory and your database is ready. Check out https://docs.djangoproject.com/en/2.2/ref/applications/#django.apps.AppConfig.ready for more details.

Good luck!

1 Like
3

Hey, Thanks for the answer, it makes a lot of sense now! One last thing, there are so many topics when going through the django documentation that it seems that if I don’t go in the right order, I end in trouble. So what would be your best way to follow along in the documentation?

1 Like
4

I highly recommend over-skimming the docs from time-to-time. Let’s say you have the section up on different form fields. Most Django users are aware of the 3 to 6 common field types, but there are three or four times that many types. I have learned a lot over the years but making myself more aware of what exists (even if all I do is read the side bar contents) helps in the long run.

I like to look for the phrase, “New in Django” while in the docs to highlight what has recently changed and to know if I pick up an older codebase what to not use.

Other than that, I tend to search outside of the docs while paying attention to djangoproject.com, blogs, and stack overflow links.

1 Like
5

Thanks a lot, I will keep these tips in mind!

1 Like