Django Notes

June 9, 2019 667 words 4 minutes

Contents

Start the Django project (foo as the project name and bar as the app name)
The admin site
The Django shell (Control-d to exit)
Making pages
References

Start the Django project (foo as the project name and bar as the app name)

Create a virtual environment (where we can install packages and isolate them from all other packages): (venv is the virtual environment module.)
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python3 -m venv foo
Activate the virtual environment: (Packages inside will be available only when the environment is active.) (use deactivate to deactivate.)
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source foo/bin/activate
Install Django (Note: use python and pip instead of python3 or pip3) in the virtual environment.
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pip install django
Start the project. (The dot at the end creates the project with a directory structure, i.e. with __init__.py, settings.py, urls.py, and wsgi.py (web server gateway interface.))
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django-admin startproject foo .
Create the database (SQLite): (Run the command anytime we modify the database.)
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python manage.py migrate
Start and view the project:
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python manage.py runserver
A Django project is a group of individual apps that work together. Let’s start an app: （creating the following in the bar folder: __init__.py, admin.py, apps.py, migrations, models.py, test.py, and view.py.）
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python manage.py startapp bar

Code-wise, a model is just a class. An example model:

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from django.db import models

# Create your models here.
class Topic(models.Model):
    """The class that manages the topic the user is learning about."""
    text = models.CharField(max_length=200)
    date_added = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        """The string representation of the model."""
        return self.text

Activate the models:

Add the apps to INSTALLED_APPS in settings.py;

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INSTALLED_APPS = [
    # My apps
    'bar',

    # Default django apps
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

Migrate:

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python manage.py makemigrations bar
python manage.py migrate

The admin site

Add a superuser: (Django only stores the hash of the password)
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python manage.py createsuperuser

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from django.contrib import admin

# Register your models here.

from .models import Topic, Entry # . means looking for the file in the same directory as admin.py

admin.site.register(Topic)
admin.site.register(Entry)

The Django shell (Control-d to exit)

Example:

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python manage.py shell
>>> from bar.models import Topic
>>> Topic.objects.all() # returns a queryset

Making pages

Defining URLs:

Include the URLs in foo/urls.py:

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from django.contrib import admin
from django.urls import path, include

urlpatterns = [
    path('admin/', admin.site.urls),
    path('', include('bar.urls')),
]

Create a new bar/urls.py file and add the following:

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from django.urls import path

from . import views

app_name = 'bar'
urlpatterns = [ # a list of individual pages that can be requested.
    # Homepage
    path('', views.index, name='index'), # '' means the base URL; call the index() function in views.py
]

Writing views:

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from django.shortcuts import render

def index(request):
    """The homepage."""
    return render(request, 'bar/index.html')

Writing templates:

Make the directory bar/templates/bar

Write the file index.html:

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<p>Learning Log</p>

<p>Learning Log helps you keep track of your learning, for any topic you're learning about.</p>

If we see the error: ModuleNotFoundError: No module named 'learning_logs.urls', just CTRL-C and rerun the server by python manage.py runserver.

Template inheritance:

Make a base.html file and include it on every page: (template tag:{percent percent}; bar is the namespace defined in bar/urls.py app_name) (in reality, use % instead of percent! here is just for avoiding the markdown error.)
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<p> <a href="{percent url 'bar:index' percent}">Foo</a> </p> {percent block content percent}{percent endblock content percent}

Inherit the base.html: (index.html)

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{percent extends "bar/base.html" percent}

{percent block content percent}
<p>Learning Log helps you become a better learner by keeping track of the topic you're learning.</p>
{percent endblock content percent}

References

Python Crash Course, 2nd Edition: A Hands-On, Project-Based Introduction to Programming