How to Lazy Load a model in a managers to stop circular imports?

Question

In Django you can create managers for your models. I do this by added a new file called managers.py and in my model objects = MyManager().

To stop circular imports I do self.model. However, if I need to reference a different model in my manager i.e.

from models import SecondModel
second= SecondModel(name=test).save()
self.model(second=second)

I get the following error: ImportError: cannot import name SecondModel

So is there a way in Django to lazy load a model?

score 38 · Answer 1 · edited May 23 '17 at 12:26

38

The currently accepted answer is deprecated as of Django 1.7; from this answer, you can adapt your code like this.

from django.apps import apps

class SomeModelManager(...):
    ...

    def some_function(self):
        model = apps.get_model(app_label='your_app', model_name='YourModel')

edited May 23 '17 at 12:26

Community

1
1

answered Nov 17 '15 at 00:13

Saturnix

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How do I import enum object which contain choices from models? – Михаил Павлов Jul 31 '17 at 08:34
@МихаилПавлов put the choices in the model class. – Florian Jul 06 '19 at 07:44
1

How can I do this with typechecking if `some_function` returns an instance of `YourModel`? i.e. `def some_function(self) -> YourModel:` – Andrew Oct 02 '20 at 02:39

score 17 · Accepted Answer · edited May 23 '17 at 10:29

You have a few options:

1. Import by name

Django has a utility function for importing by string name so you don't need to import yourself. There are several methods available for this (see this question: Django: Get model from string?)

from django.db.models.loading import get_model

class SomeModelManager(...):
    ...

    def some_function(self):
        model = get_model('your_app', 'YourModel')
        object = model()

2. Imports at the bottom

Add the import at the bottom of the managers.py file and make sure to simply import the module and not the models themselves.

So...

models.py:

import managers

class SomeModel(models.Model):
    ...
    objects = managers.SomeModelManager()

managers.py

class SomeModelManager(...):
    ...

    def some_function(self):
        object = models.SomeOtherModel()

import models

does Django not have a lazy import? I was always told that imports at the bottom of the page were bad! — Prometheus, Apr 20 '15 at 09:57
@OrbiterFleet: true, I've added that as an alternative option :) — Wolph, Apr 20 '15 at 10:49

How to Lazy Load a model in a managers to stop circular imports?

2 Answers2

1. Import by name

2. Imports at the bottom

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