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Unable to call a class using Django

If I do that :
from myapp import models
User.objects.first()
I got that error :
NameError : name 'User' is not defined
whereas if I do that
import myapp
myapp.models.User.objects.first()
it works
I don't understand at all why I have that problem
Thank you very much for your help !

Replace:
from myapp import models
with the following:
This way, you are telling Django which model classes to import rather than leaving Django guessing what to do with it.
It prevents you from loading unnecessary models which might not be used right away and could potentially increase load time.
from myapp.models import User

In your example, your have not imported class User actually. You have imported it's module called models
You can do one of these:
from myapp import models
models.User.objects.first()
Or:
from myapp.models import User
User.objects.first()

Importing Model Class into another app - Django

I am trying to import a model class from another app. My structure looks like the following:
mysite/
-- main/
models.py
-- webshop/
models.py
I'd like to import a model class from my webshop app into the main/models.py. I run the following in my main/models.py file:
from django.db import models
from ..webshop.models import Item
# Create your models here.
class Test(models.Model):
item = models.ForeignKey(Item, on_delete=models.CASCADE)
In my text editor everything seems fine. It finds the appropriate app and finds the model class Item which I need to import there.
When I run makemigrations I am getting the following error:
ValueError: attempted relative import beyond top-level package
I've read some other questions on SO on how to make this work but can't figure it out. Tried:
mysite.webshop.models import Item
aswell. But then I get a: ModuleNotFoundError: No module named 'mysite.webshop'.
Does anyone have suggestions?

From the error ValueError: attempted relative import beyond top-level package, I'm going to assume in your text editor, your current working directory is mysite/. And so using ..webshop.models you're trying to go up two directories above mysite/ which is why you're getting the error.
What you need to do is:
from django.db import models
from webshop.models import Item

Expose a Django app's models at the module level

I've made a django app, which is designed to be easily pluggable, and only has 1 view, and 1 model that project planning to use the app need to be aware of.
For ease, I'd like to just make the view and model available from the app-level. So rather than:
from mything.views import MyView
from mything.models import MyModel
You can instead just do:
from mything import MyView, MyModel
I changed the __init__.py file in the app to be like this:
from .views import MyView
from .models import MyModel
Of course I get the old django.core.exceptions.AppRegistryNotReady raised, since it's attempting to run the models.py code before the apps are loaded.
So I came up with the following workaround, and I'm wondering if it's a reasonable pattern to use or not. Now in __init__.py I have:
def _expose_items():
from .views import MyView
from .models import MyModel
globals()['MyView'] = MyView
globals()['MyModel'] = MyModel
And in my app's apps.py:
from . import _expose_items
class MyThingConfig(AppConfig):
name = 'mything'
def ready(self):
_expose_items()
So now indeed, I can directly import the view and model from the outside. Is this useful, or horrible?

Most Django apps do not collect views or models to the top level module. Refer to django.contrib.auth as an example.

Most Django apps do not collect views or models to the top level module. Use clear documentation to demonstrate how to import from your app. Hacks including globals() will probably create more trouble than help.
Refer to django.contrib.auth as an example.

Python, Flask, SQLAlchemy: cannot import from models

I've got a weird problem.
I am building a Flask app with SQLAlchemy. I have a file with models, namely, models.py. And I have a User model there.
If I open my "views.py" and insert a string
import models
and then use the User model like
u=models.User.query.filter_by(name='John',password='Doe').first()
everything works fine.
But if instead of "import models" i put
from models import User
Python crashes and says:
ImportError: cannot import name User
how can this be possible?

you most likely have a circular import; your, lets say 'app' module:
# app.py
import models
...
def doSomething():
models.User....
but your models module also imports app
import app
class User:
...
since models imports app, and app imports models, python has not finished importing models at the point app tries to import models.User; the User class has not been defined (yet). Either break the cyclic import (make sure models doesn't import anything that also imports models), or you'll just have to make do with models.User instead of the shorter User in app.

Instead of
from models import User
use
from models import *

In this case, you are importing the models into views.py therefore if you need a class from models, import it from views.py and the circular import problem will be resolved.

ReferenceField in mongoengine

I use mongoengine with django. I have two applications with models.
app1/models.py:
from mongoengine import fields
from mongoengine.document import Document
class Model1(Document):
name = fields.StringField()
lists = fields.ListField(fields.ReferenceField("Model2", dbref=False))
app2/models.py:
from mongoengine import fields
from mongoengine.document import Document
class Model2(Document):
name = fields.StringField()
All applications were added to INSTALLED_APPS. When I use the django dev-server, everything is fine. But using this code with uwsgi-server there is an error:
Model2 has not been registered in the document registry.
Importing the document class automatically registers it, has it
been imported?
What I should do?

You should import app2.models somewhere. Put a comment by the import saying why it's there, so nobody removes the useless-looking import in the future.
When the django dev server starts up it imports the models from all installed apps and validates them. You'll see
Validating models...
0 errors found
This does not happen in a production environment. It is just a nicety of the dev server.