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Building a page with data

Most pages in a project need to present data that’s specific to the current user.

URL parameters

A URL often needs to accept a parameter telling it which data to access from the database. The second URL pattern shown here looks for the ID of a specific topic and stores it in the parameter topic_id.

urlpatterns = [
  url(r'^$', views.index, name='index'),
  url(r'^topics/(?P<topic_id>\d+)/$',
  views.topic, name='topic'),
]

Using data in a view

The view uses a parameter from the URL to pull the correct data from the database. In this example the view is sending a context dictionary to the template, containing data that should be displayed on the page.

def topic(request, topic_id):
  """Show a topic and all its entries."""
  topic = Topics.objects.get(id=topic_id)
  entries = topic.entry_set.order_by('-date_added')
  context = {
    'topic': topic,
    'entries': entries,
  }
  return render(request,
    'learning_logs/topic.html', context)

Using data in a template

The data in the view function’s context dictionary is available within the template. This data is accessed using template variables, which are indicated by doubled curly braces. The vertical line after a template variable indicates a filter. In this case a filter called date formats date objects, and the filter linebreaks renders paragraphs properly on a web page

{% extends 'learning_logs/base.html' %}
{% block content %}
 <p>Topic: {{ topic }}</p>
 <p>Entries:</p>
 <ul>
 {% for entry in entries %}
 <li>
 <p>
 {{ entry.date_added|date:'M d, Y H:i' }}
 </p>
 <p>
 {{ entry.text|linebreaks }}
 </p>
 </li>
 {% empty %}
 <li>There are no entries yet.</li>
 {% endfor %}
 </ul>

{% endblock content %}

Template Inheritance

Template InheritanceMany elements of a web page are repeated on every page in the site, or every page in a section of the site. By writing one parent template for the site, and one for each section, you can easily modify the look and feel of your entire site.

The parent template

The parent template defines the elements common to a set of pages, and defines blocks that will be filled by individual pages

<p>
 <a href="{% url 'learning_logs:index' %}">
 Learning Log
 </a>
</p>
{% block content %}{% endblock content %}

The child template

The child template uses the {% extends %} template tag to pull in the structure of the parent template. It then defines the content for any blocks defined in the parent template.

{% extends 'learning_logs/base.html' %}
{% block content %}
 <p>
 Learning Log helps you keep track
 of your learning, for any topic you're
 learning about.
 </p>
{% endblock content %}

Another model

A new model can use an existing model. The ForeignKey attribute establishes a connection between instances of the two related models. Make sure to migrate the database after adding a new model to your app.

Defining a model with a foreign key

class Entry(models.Model):
 """Learning log entries for a topic."""
  topic = models.ForeignKey(Topic)
  text = models.TextField()
  date_added = models.DateTimeField(
  auto_now_add=True)

  def __str__(self):
    return self.text[:50] + "..."

Building a simple homepage

Users interact with a project through web pages, and a project’s home page can start out as a simple page with no data. A page usually needs a URL, a view, and a template.

Mapping a project’s URLs

The project’s main urls.py file tells Django where to find the urls.py files associated with each app in the project

from django.conf.urls import include, url
from django.contrib import admin
urlpatterns = [
  url(r'^admin/', include(admin.site.urls)),
  url(r'', include('learning_logs.urls',
  namespace='learning_logs')),
]

Mapping an app’s URLs

An app’s urls.py file tells Django which view to use for each URL in the app. You’ll need to make this file yourself, and save it in the app’s folder.

from django.conf.urls import url
from . import views
urlpatterns = [
  url(r'^$', views.index, name='index'),
]

Writing a simple view

A view takes information from a request and sends data to the browser, often through a template. View functions are stored in an app’s views.py file. This simple view function doesn’t pull in any data, but it uses the template index.html to render the home page

from django.shortcuts import render
def index(request):
  """The home page for Learning Log."""
  return render(request, 'learning_logs/index.html')

Writing a simple template

A template sets up the structure for a page. It’s a mix of html and template code, which is like Python but not as powerful. Make a folder called templates inside the project folder. Inside the templates folder make another folder with the same name as the app. This is where the template files should be saved

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

Working with Model

Defining a model

To define the models for your app, modify the file models.py that was created in your app’s folder. The __str__() method tells Django how to represent data objects based on this model.

from django.db import models
class Topic(models.Model):
 """A topic the user is learning about."""
  text = models.CharField(max_length=200)
  date_added = models.DateTimeField(
  auto_now_add=True)

  def __str__(self):
    return self.text

Activating a model

To use a model the app must be added to the tuple INSTALLED_APPS, which is stored in the project’s settings.py file.

INSTALLED_APPS = (
  --snip--
  'django.contrib.staticfiles',

  # My apps
  'learning_logs',
)

Migrating the database

The database needs to be modified to store the kind of data that the model represents.

$ python manage.py makemigrations learning_logs 
$ python manage.py migrate

Creating a superuser

A superuser is a user account that has access to all aspects of the project.

$ python manage.py createsuperuser

Registering a model

You can register your models with Django’s admin site, which makes it easier to work with the data in your project. To do this, modify the app’s admin.py file. View the admin site at http://localhost:8000/admin/.

from django.contrib import admin
from learning_logs.models import Topic
admin.site.register(Topic)

Starting a Project

Create a virtual environment

$ virtualenv venv 
$ source venv/bin/activate

Install Django

$ pip install Django

Setup Django Project

$ django-admin.py startproject projectname

Create database

$ python manage.py syncdb

Run Server

$ python manage.py runserver

Create App

$ python manage.py startapp appname

Add to INATALLED_APPS list

Create Templates

$ mkdir appname/templates
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