Category: Computer

A Wedge of Django: Covers Python 3.8 and Django 3.x
We also get some points from this book…

• Terminology “Wire in the URL”, meaning to associate the Django view with a web location on the site.
• Python List: a list consists of comma-separated values wrapped in square brackets
  ['Abc', 2, 'Fine', 3, 4]
• Python Dictionary: A set of key: value pairs
  {
    'a1': 'Model A',
    'B3': 'Color 1',
    'coffee': 'cafe',
}

• <p>{{ my_statement }}</p>
  The curly braces around my_statement mean that it won’t be displayed on the page as-is.
  It’ll be evaluated on the Python side and then the result will be displayed. It can be any of the following:
  • A Python expression, e.g., string, number, or instantiated object
  • A function or method call
• Create a PostgreSQL database and add the database configuration in config\settings\base.py
  Setting the environment variable: DATABASE_URL environment variable
  DATABASES = {
    # Raises ImproperlyConfigured Exception
    # if DATABASE_URL Not in os.environ
    "default": env.db(
        "DATABASE_URL", default="postgres://db_username:[email protected]:5432/db_name",
    )
}
• <p>{{ object.bio|linebreaksbr }}<p>
  The “|” or “pipe” symbol in a template is a “filter”. Filters are used to modify variables in Django Templates.
  The “linebreakbr” filter modifies text to replace every carriage return with the HTML <br> tag in teh page being rendered.
• assert key, is used when debugging code. It lets you test if a condition in your code
  returns True, if not, the program will raise an AssertionError.
  x = 1
 
#if condition returns True, then nothing happens:
assert x == 1
 
#if condition returns False, AssertionError is raised:
assert x == 2

• It is a common practice in the Django world to keep all our Django apps inside one directory.
• A good rule of thumb is to use TextField rather than CharField whenever there might be a need for more than 255 characters.
• Don’t Use list_editable.
  As records are tracked not by primary keys but by their position in a displayed list.
• CBV (Class-based View)
  from django.http import HttpResponse
from django.views.generic import View
 
class MyView(View):
 
    def get(self, request, *args, **kwargs):
        return HttpResponse('Response to GET request')
 
    def post(self, request, *args, **kwargs):
        return HttpResponse('Response to POST request')
 
    def delete(self, request, *args, **kwargs):
        return HttpResponse('Response to DELETE request')

  FBV (Function-based View)
  def my_view(request, *args, **kwargs):
    if request.method == 'POST':
        return HttpResponse('Response POST request')
    elif request.method == 'DELETE':
        return HttpResponse('Response DELETE request')
    return HttpResponse('Response GET request')

  or this FBV approach:
  def my_view(request, *args, **kwargs):
    METHOD_DISPATCH = {
      'POST': HttpResponse('Response POST request'),
      'DELETE': HttpResponse('Response DELETE request'),
    }
    DEFAULT = HttpResponse('Response GET request')
    return METHOD_DISPATCH.get(request.method, DEFAULT)

• HTTP methods used by clients (web browsers) to access application servers (Django).
  GET: Used to read web pages
  POST: Used to submit forms
  DELETE: Used with an API to delete a resource such as a web page
• In a DetailView’s template, the object is accessible as the lowercased model name.
• get_FOO_display() is a utility method created automatically for any Django model field.
• We set blank=True for the optional field. But we don’t set null=True because Django’s convention is to store empty values as the empty string, and to retrieve NULL/empty values as the empty string.

To be continued…

Readings:
บล็อกของ phyblas
Qiita (@phyblas)
django-braces’s documentation
Class-based View
What is a REPL?
How to configure your Django project for multiple environments?
Deploy A Django Project
Deploying a Django application in Windows with Apache and mod_wsgi
How to Remove Services in Windows 10
Anaconda + Django + Apache Webserver
How to run Django on Apache using Windows 10, Virtualenv Python and mod_wsgi
Manage your Python Virtual Environment with Conda
Deploying Django on Windows Server 2019 and Apache with MOD_WSGI

Just bought this book from feldroy.com.

GitHub for Two-Scoop-of-Django-3.x

Key Points:

• Keep It Simple, Stupid
• Fat Models, Utility Modules, Thin Views, Stupid Templates
• Follow the PEP8;
  • Use 4 spaces per indentation level.
  • Separate top-level function and class definitions with two blank lines.
  • Method definitions inside a class are separated by a single blank line.
• Limit of text per line is 79 characters (for private projects, it is relaxed to 99 characters).
• The imports should be grouped in the following order:
  • Standard library imports
  • Core Django imports
  • Related third-party imports
  • Local application or library-specific imports
• Using aliases to avoid Python Module collisions
  from django.db.models import CharField as ModelCharField
from django.forms import CharField as FormCharField

• Use underscores in URL Pattern Names rather than dashes
  patterns = [
    path(route='add/',
        view=views.add_topping,
        name='toppings:add_topping'),
    ]

  Dashes in actual URLs are fine (e.g. route=‘add-topping/’).
• Using static/ for the (non-user-generated) static media directory.
• A Django project is a web application powered by the Django web framework.
  Django apps are small libraries designed to represent a single aspect of a project. A Django project is made up of many Django apps. Some of those apps are internal to the project and will never be reused; others are third-party Django packages.
  INSTALLED_APPS is the list of Django apps used by a given project available in its INSTALLED_APPS setting.
  Third-party Django packages are simply reusable Django apps that have been packaged with the Python packaging tools.
• Each app should be tightly focused on its task.
  James Bennett: “The art of creating and maintaining a good Django app is that it should follow the truncated Unix philosophy according to Douglas McIlroy: ‘Write programs that do one thing and do it well.’“
• Name the Django Apps
  • Keep to single word names, like flavors, animals, blog, and finances.
  • The app’s name should be a plural version of the app’s main model. There are many good exceptions, blog is the example.
  • Consider naming the app according to the URLs to be appeared. For example, http://www.example.com/weblog/, then consider naming your app weblog rather than blog, posts, or blogposts, even if the main model is Post.
  • Use PEP8-compliant, importable Python package names: short, all-lowercase names without numbers, dashes, periods, spaces, or special characters. Using underscores to separate words, although the use of underscores is discouraged.
• Try to keep your apps small.
• Sample Project Layout (any module ending with a slash (‘/’) represents a Python package)
  yourprojname_reporoot #This is the <repository_root>.
|--config/
|  |--settings/
|  |--__init__.py
|  |--asgi.py
|  |--urls.py
|  |--wsgi.py
|--docs/
|--yourprojname_project/ #The <django_project_root> of the project.
|  |--media/ #development only!
|  |--apps1/
|  |--apps2/
|  |--apps3/
|  |--static/ #Non-user-generated static media assets (CSS, JavaScript, and images).
|  |--templates/ #Your site-wide Django templates
|--.gitignore
|--Makefile
|--README.md
|--manage.py
|--requirements.txt #Current dependencies ($ pip freeze > requirements.txt)

• When coding in Django, the classic example is the process of creating user objects and related data cross multiple models and apps.
• Service layer example
  
apps1/
|--api/
|--models.py
|--services.py #Service layer location for business logic
|--selectors.py #Service layer location for queries
|--tests/

• Each Django app should be tightly-focused on its own task and possess a simple, easy-to-remember name. If an app seems too complex, it should be broken up into smaller apps.
• Settings module is loaded when your server starts up.
• Instead of having one settings.py file, you have settings/ directory containing your settings files.
  (Each settings module should have its own corresponding requirements file.)
  settings/
|--__init__.py
|--base.py #Settings common to all instances of the project.
|--local.py #Settings file when working on the project locally.
|--staging.py #Staging version for running a semi-private version of the site on a production server.
|--test.py #Settings for running tests including test runners, in-memory database definitions, and log settings.
|--production.py #Settings file used by your live production server(s). Sometimes called prod.py.

  To start Python interactive interpreter with Django, using your settings/local.py settings file:
  python manage.py shell --settings=config.settings.local

  To run the local development server with your settings/local.py settings file:
  python manage.py runserver --settings=config.settings.local

• Never hardcoding file paths in Django settings files.
• The golden rule of Web application security is to never trust data from untrusted sources.
• Everything except for passwords and API keys ought to be tracked in version control.
• If there are 20+ models in a single app, break it down into smaller apps, as it probably means the app is doing too much.
  In practice, no more than five to ten models per app.
• Simple rules of thumb for knowing which type of inheritance to use and when:
  • If the overlap between models is minimal, there might not be needed for model inheritance.
    Just add the fields to both models.
  • If there is enough overlap between models, the code should be refactored so that
    the common fields are in an abstract base model.
  • Proxy models are an occasionally-useful convenient feature, but they’re very different from
    the other two model inheritance styles.
  • Avoid multi-table inheritance. Instead of multi-table inheritance, use explicit OneToOneFields and ForeignKeys
    between models so you can control when joins are traversed.
• It’s very common in Django projects to include a created and modified timestamp field on all models.

To be continued…

Further readings:
The Twelve-Factor App
PEP8 — Style Guide for Python Code