Sm0ke

Posted on Jun 23, 2021 • Edited on Sep 27, 2023 • Originally published at docs.appseed.us

Django Custom Commands - Tutorial for Beginners

#django #python #beginners #webdev

Hello Coders,

This article explains how to write our own Django Custom Commands that might help us to test, upload data, or extract valuable information in a production environment from a Django project. For newcomers, Django is a popular web framework designed and written in Python by experienced developers.

The main advantage of a custom command is that all Django machinery is loaded and ready to be used. That means you can import models, execute queries to the database using Django’s ORM, and interact with all your project’s resources.

Topics covered

Create a new Django App and Update Django to use it
Visualize the required directory structure inside the app
Code end execute a few custom commands:
- cmd_time.py - show current timestamp
- cmd_apps - list all registered apps
- cmd_models - list all apps and associated models
- cmd_showcfg - list all CFG keys and values
The source code can be found on Github (MIT License)

Create a new Django App

This tutorial assumes that we have a working Django project and we will move forward and create a new app via startapp subcommand:

$ python manage.py startapp app_customcmd

Inside the new app directory, we need to create a directory structure as shown below:

< PROJECT ROOT >                          <-- project directory
 |
 |-- app_customcmd/                                <-- app directory
 |    |-- management/
 |    |    +-- __init__.py
 |    |    +-- commands/
 |    |         +-- __init__.py
 |    |         +-- cmd_....py  <-- module where all commands are saved

Once we have built and configure Django to use the new app, all commands defined in commands directory are automatically discovered even without an application restart.

Configure Django to use the app

To execute our custom commands we need to activate app_customcmd in the project configuration:

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'app_customcmd',               # <-- NEW
]

Custom Commands

This section presents for custom commands that will access and report a few things related to a Django project internals - Let's go!

Show Current Time

This simple custom command help us to accommodate with the concept. Here is the code, saved in the app_customcmd/management/commands directory:

from django.core.management.base import BaseCommand
from django.utils import timezone

class Command(BaseCommand):
    help = 'Displays current time'

    def handle(self, *args, **kwargs):
        time = timezone.now().strftime('%X')
        self.stdout.write("It's %s" % time)

The actual executed code resides in the handle method and the execution should display something similar to this:

$ python manage.py cmd_time
It's 09:18:08                <-- The output from our custom CMD

The most important aspect regarding the code is the usage of BaseCommand as a super-class for our definition.

Show Registered Apps

This sample will iterate over all registered and active apps and print their names.

from django.core.management.base import BaseCommand
from django.apps import apps

class Command(BaseCommand):
    help = 'Displays registered apps'

    def handle(self, *args, **kwargs):
        for app in apps.get_app_configs():
            self.stdout.write(" APP -> %s" % app.verbose_name)

Script execution and output:

$ python manage.py cmd_apps
 APP -> Administration                     # Default Django App   
 APP -> Authentication and Authorization   # Default Django App
 APP -> Content Types                      # Default Django App
 APP -> Sessions                           # Default Django App
 APP -> Messages                           # Default Django App
 APP -> Static Files                       # Default Django App
 APP -> App_Customcmd                      # <-- Our NEW App

Show models for each app

This command is quite similar with the previous one, but provide also the registered models for each app.

from django.core.management.base import BaseCommand

from django.apps import apps

class Command(BaseCommand):
    help = 'Displays registered apps and models'

    def handle(self, *args, **kwargs):

        # Iterate over apps
        for app in apps.get_app_configs():
            self.stdout.write(" APP -> %s" % app.verbose_name)

            # Iterate over models                                # <-- New Code 
            for model in app.get_models():                       # <-- New Code 
                self.stdout.write("\t |- (model) -> %s" % model) # <-- New Code

The execution and output

$ python manage.py cmd_models
 APP -> Administration
         |- (model) -> <class 'django.contrib.admin.models.LogEntry'>
 APP -> Authentication and Authorization
         |- (model) -> <class 'django.contrib.auth.models.Permission'>
         |- (model) -> <class 'django.contrib.auth.models.Group'>
         |- (model) -> <class 'django.contrib.auth.models.User'>
 APP -> Content Types
         |- (model) -> <class 'django.contrib.contenttypes.models.ContentType'>
 APP -> Sessions
         |- (model) -> <class 'django.contrib.sessions.models.Session'>        
 APP -> Messages
 APP -> Static Files
 APP -> App_Forms
 APP -> App_Pdf
 APP -> App_Customcmd
 APP -> App
         |- (model) -> <class 'app.models.Book'>

Print Config Variables

This custom command scan the settings object for proprieties and print all values.

from django.core.management.base import BaseCommand
from django.utils import timezone

from django.conf import settings

class Command(BaseCommand):
    help = 'Displays project config'

    def handle(self, *args, **kwargs):

        # type( settings ) => <class 'django.conf.LazySettings'>
        # settings.__dict__

        # Iterate over apps
        for key in settings.__dict__.keys():

            self.stdout.write(" Cfg Key: " + key + " -> %s" % settings.__dict__[ key ] )

The output and execution:

(env) PS D:\work\repo-samples\django-learn-by-coding> python manage.py cmd_showcfg
 Cfg Key: _wrapped -> <Settings "config.settings">
 Cfg Key: INSTALLED_APPS -> ['django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.staticfiles', 'app_forms', 'app_pdf', 'app_customcmd', 'app']
 Cfg Key: DEBUG -> True
 Cfg Key: LOGGING_CONFIG -> logging.config.dictConfig
 Cfg Key: LOGGING -> {}
 Cfg Key: DEFAULT_EXCEPTION_REPORTER -> django.views.debug.ExceptionReporter
 Cfg Key: FORCE_SCRIPT_NAME -> None
 Cfg Key: DEFAULT_TABLESPACE ->
 Cfg Key: DEFAULT_AUTO_FIELD -> django.db.models.BigAutoField
 Cfg Key: ABSOLUTE_URL_OVERRIDES -> {}
 Cfg Key: AUTH_USER_MODEL -> auth.User
 Cfg Key: DATABASES -> {'default': {'ENGINE': 'django.db.backends.sqlite3', 'NAME': WindowsPath('D:/work/repo-samples/django-learn-by-coding/db.sqlite3'), 'ATOMIC_REQUESTS': False, 'AUTOCOMMIT': True, 'CONN_MAX_AGE': 0, 'OPTIONS': {}, 'TIME_ZONE': None, 'USER': '', 'PASSWORD': '', 'HOST': '', 'PORT': '', 'TEST': {'CHARSET': None, 'COLLATION': None, 'MIGRATE': True, 'MIRROR': None, 'NAME': None}}}
...
(truncated output)

Writing custom commands in our Django projects might help us to extract stats, execute cron jobs, and check the health of a project that runs in production.