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On Saturday, you can write and deploy a web application. It's an online poll where visitors can view choices (a bit of text, plus an image) and vote the option up and down.
'''Note''': This is one ''long'' page. It will take most of the afternoon to go through it.
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This is based ''heavily'' on the official tutorial for the Django web programming framework.
This page should say what you should actually expect to know. It is okay that you don't understand everything you are typing in. After a lot more learning, you will be able to. The first time, though, it's okay if you don't. Will and Katie have feedback for this page.
== Writing your first Django app, part 1 ==
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Let’s learn by example.
It’ll consist of two parts:
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=== Look at the files ===
Let’s look at files
workshop_mysite/
public/
README.mediawiki
__init__.py
manage.py
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These files are:
* README.mediawiki: Many projects come with ''README'' files that, well, you should read. This one does, too.
* public/: This directory contains files the instructors put together so you can easily deploy your web app to Alwaysdata.com.
* __init__.py: An empty file that tells Python that this directory should be considered a Python module. Because of the __init__.py file, you can use ''import'' to ''import workshop_mysite''.
* manage.py: A command-line utility that lets you interact with this Django project in various ways. You can read all the details about manage.py in django-admin.py and manage.py.
* settings.py: Settings/configuration for this Django project. Django settings will tell you all about how settings work.
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=== The development server ===
Let's verify this worked.
<pre>
python manage.py runserver
</pre>
You'll see the following output on the command line:
<pre>
Validating models...
0 errors found.
Django version 1.
Development server is running at http://127.0.0.1:8000/
Quit the server with CONTROL-C.
</pre>
You've started the Django development server, a lightweight Web server written purely in Python. The Django maintainers include this web server, but on a "deployment" like alwaysdata.com, you typically tie Django into an existing server like Apache.
Now that the server's running, visit http://127.0.0.1:8000/ with your Web browser. You'll see a "Welcome to Django" page, in pleasant, light-blue pastel. It worked!
Exit the server by pressing CONTROL-C on your keyboard.
=== Fixing security settings ===
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=== Database setup ===
Keep looking at settings.py:
The value is itself another dictionary with information about the site's default database. You can see from the ''NAME'' that the Django project uses a file called ''database.db'' to store information.
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Here are the things to know:
* An ''app'' is component of a website that does something. For example, the ''Django administration'' app is something you'll see later in this tutorial.
* A ''project'' corresponds to a website: it contains a '''settings.py''' file, so it has a corresponding database.
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In our simple poll app, we'll create two models: polls and choices. A poll has a question and a publication date. A choice has two fields: the text of the choice and a vote tally. Each choice is associated with a poll. (FIXME: Add image to Choice.)
These concepts are represented by
from django.db import models
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class Poll(models.Model):
question = models.CharField(max_length=200)
pub_date = models.DateTimeField(
class Choice(models.Model):
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choice = models.CharField(max_length=200)
votes = models.IntegerField()
Save the models.py file.
All models in Django code are represented by a class that subclasses django.db.models.Model. Each model has a number of class variables, each of which represents a database field in the model.
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Each field is represented by an instance of a Field class -- e.g., CharField for character fields and DateTimeField for datetimes. This tells Django what type of data each field holds.
The name of each Field instance (e.g. question or pub_date
Some Field classes have required elements. CharField, for example, requires that you give it a max_length. That's used not only in the database schema, but in validation, as we'll soon see.
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'polls',
)
Save the settings.py file.
Now Django knows to include the polls app.
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Read the django-admin.py documentation for full information on what the manage.py utility can do.
=== Playing with the API ===
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[<Poll: Poll object>]
Wait a minute. <Poll: Poll object> is
Use your '''text editor''' to open the polls/models.py file and adding a __unicode__() method to both Poll and Choice:
class Poll(models.Model):
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Note the addition of import datetime to reference Python's standard datetime module.
FIXME: add explanation of why we did this
Save these changes to the models.py file, and then start a new Python interactive shell by running python manage.py shell again:
>>> from polls.models import Poll, Choice
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If you want to search your database, you can do it using the '''filter''' method on the ''objects'' attribute of Poll. For example:
>>>
>>>
[<Poll: What's up?>]
>>>
1
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Right now, we have a Poll in the database, but it has no Choices. See:
>>> p = Poll.objects.get(
>>> p.choice_set.all()
[]
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<Choice: The sky>
>>> c = p.choice_set.create(choice='Just hacking again', votes=0)
>>> c
<Choice: Just hacking again>
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=== Visualize the database in SQLite Manager ===
When you call ''.save()'' on a model instance, Django saves that to the database. (Remember, Django is a web programming framework built around the idea of saving data in a SQL database.)
Where ''is'' that database? Take a look at '''settings.py''' in your text editor. You can see that ''database.db'' is the filename. In '''settings.py''' Python calculates the path to the current file.
So now:
* Open up Firefox
* Find SQLite Manager in '''Tools'''->'''SQLite Manager'''
* In the SQLite Manager menus, choose: '''Database'''->'''Connect Database'''
* Find the '''workshop_mysite/database.db''' file.
Browse your tables! This is another way of looking at the data you just created.
'''Note''': In order to find the ''database.db'' file, you might need to ask SQLite Manager to show you all files, not just the ''*.sqlite'' files.
I (the author of this tutorial) think it's really important that you be able to find this database file. So go ahead and do this step. Browse around! Hooray.
When you're satisfied with your Poll data, you can close it.
=== Save and share our work ===
We've done something! Let's share it with the world.
We'll do that with ''git'' and ''Github''. On your own computer, get to a Terminal or a GitBash.
Use '''cd''' to get into the '''workshop_mysite''' directory. If it's a fresh Terminal, this is what you'll do:
cd Desktop
cd django_projects
cd workshop_mysite
Use ''git add'' to add the content of your files to git:
git add polls/*.py
And use ''git commit'' to ''commit'' those files:
git commit -m "I made these files and this is a message describing them"
Finally, use ''git push'' to push those up to your Github repository:
git push
Go to your Github account. Find the ''workshop_mysite'' repository. Do you see your files?
If so, proceed!
=== Enough databases for now ===
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ROOT_URLCONF = 'workshop_mysite.urls'
That means that the default URLconf
Time for an example. Edit
<pre>
from django.conf.urls.defaults import *
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(r'^polls/(\d+)/vote/$', 'polls.views.vote'),
)
</pre>
This is worth a review. When somebody requests a page from your Web site -- say, "/polls/23/", Django will load the ''urls.py'' Python module, because it's pointed to by the ROOT_URLCONF setting. It finds the variable named urlpatterns and traverses the regular expressions in order. When it finds a regular expression that matches -- r'^polls/(\d+)/$' -- it loads the function detail() from polls/views.py. Finally, it calls that detail() function like so:
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return HttpResponse("Hello, world. You're at the poll index.")
This is the simplest view possible.
Now
def detail(request, poll_id):
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return HttpResponse("You're voting on poll %s." % poll_id)
=== Write views that actually do something ===
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All Django wants is that HttpResponse. Or an exception.
Most of the Django views in the world use Django's own database API, which we covered in Tutorial 1. Let's do that, too. Here's one stab at the index() view, which displays the latest 5 poll questions in the system, separated by commas, according to publication date. Continue editing the file views.py:
from polls.models import Poll
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return HttpResponse(output)
Now go to "http://localhost:8000/polls/" in your Web browser. You should see the text of the first poll. There's a problem here, though: The page's design is hard-coded in the view. If you want to change the way the page looks, you'll have to edit this Python code. So let's use Django's template system to separate the design from Python:
from django.shortcuts import render_to_response
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</pre>
Load the page
=== Raising 404 ===
Now, let's tackle the poll detail view -- the page that displays the question for a given poll. Continue editing the ''views.py'' file. This view uses Python ''exceptions'':
from django.http import Http404
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def detail(request, poll_id):
try:
p = Poll.objects.get(
except Poll.DoesNotExist:
raise Http404
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The new concept here: The view raises the Http404 exception if a poll with the requested ID doesn't exist.
If you'd like to quickly get the above example working, just create a new template file and name it ''detail.html''. Enter in it just one line of code:
<pre>
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</pre>
Does your detail view work? Try it: http://127.0.0.1:8000/polls/1/
=== Adding more detail ===
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Method-calling happens in the {% for %} loop: poll.choice_set.all is interpreted as the Python code poll.choice_set.all(), which returns a sequence of Choice objects and is suitable for use in the {% for %} tag.
Load the new detail page in your browser: http://127.0.0.1:8000/polls/1/ The poll choices now appear.
=== Adding some style ===
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FIXME: CSS
== Part 3: Let people vote ==
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* Since we're creating a POST form (which can have the effect of modifying data), we need to worry about Cross Site Request Forgeries. Thankfully, you don't have to worry too hard, because Django comes with a very easy-to-use system for protecting against it. In short, all POST forms that are targeted at internal URLs should use the {% csrf_token %} template tag.
The {% csrf_token %} tag requires information from the request object, which is not normally accessible from within the template context. To fix this, a small adjustment needs to be made to the detail view in the "views.py" file, so that it looks like the following:
<pre>
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</pre>
The details of how this works are explained in the [http://docs.djangoproject.com/en/dev/ref/templates/api/#subclassing-context-requestcontext documentation for RequestContext].
Now, let's create a Django view that handles the submitted data and does something with it. Remember, in Tutorial 3, we created a URLconf for the polls application that includes this line:
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Does it work?! If so, show your neighbor!
== Part 3.5: Deploy
You've done a lot of work. It's time to share it with the world.
This workshop follows a workflow very similar to what I personally use in my professional Django projects: using ''git'' to store the history of my project on my computer, and using that to synchronize with a web server other people can see.
You've already pushed some work to Github. To get our changes over to alwaysdata. you'll:
# Add and commit files on your own computer.
# Push your changes to Github.
# Connect to your alwaysdata.com account via SSH/PuTTY
# Run "git pull" to get the latest version to your Alwaysdata account.
So we'll do those steps in order.
To do the ''add and commit'', open up your Terminal or GitBash:
git add .
git commit -m "More changes"
To push:
git push
Now, open up SSH or PuTTY and connect to your alwaysdata.com account.
Finally, in '''that''' terminal:
cd workshop_mysite
git pull
Okay, not quite finally. You might need to go to https://admin.alwaysdata.com/advanced/processes/ and click ''Restart my applications''.
Go to your alwaysdata site's /polls/ page. For me, I'd go to:
* http://paulproteus.alwaysdata.com/polls/
You should see your poll!
== Part 4: Editing your polls in the Django admin interface ==
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* An unnecessary lack of color.
Generating admin sites for your staff or clients to add, change and delete content is tedious work that doesn’t require much creativity. For that reason, Django entirely automates creation of admin interfaces for models.
Django was written in a newsroom environment, with a very clear separation between “content publishers” and the “public” site. Site managers use the system to add news stories, events, sports scores, etc., and that content is displayed on the public site. Django solves the problem of creating a unified interface for site administrators to edit content.
The admin isn’t necessarily intended to be used by site visitors; it’s for site managers.
=== Activate the admin site ===
The Django admin site is not activated by default – it’s an opt-in thing. To activate the admin site for your installation, do these three things:
* Open up '''workshop_mysite/settings.py''' and add "django.contrib.admin" to your INSTALLED_APPS setting.
* Run python manage.py syncdb. Since you have added a new application to INSTALLED_APPS, the database tables need to be updated.
* Edit your '''workshop_mysite/urls.py''' file and uncomment the lines that reference the admin – there are three lines in total to uncomment.
=== Start the development server ===
Let’s make sure the development server is running and explore the admin site.
Try going to http://127.0.0.1:8000/admin/. If it does not load, make sure you are still running the development server. You can start the development server like so:
python manage.py runserver
http://127.0.0.1:8000/admin/ should show you the admin site's login screen.
=== Enter the admin site ===
Now, try logging in. (You created a superuser account earlier, when running ''syncdb'' for the fist time. If you didn't create one or forgot the password you can create another one.) You should see the Django admin index page.
You should see a few other types of editable content, including groups, users and sites. These are core features Django ships with by default.
=== Make the poll app modifiable in the admin ===
But where's our poll app? It's not displayed on the admin index page.
Just one thing to do: We need to tell the admin that Poll objects have an admin interface. To do this, create a file called admin.py in your polls directory, and edit it to look like this:
<pre>
from polls.models import Poll
from django.contrib import admin
admin.site.register(Poll)
</pre>
You'll need to restart the development server to see your changes. Normally, the server auto-reloads code every time you modify a file, but the action of creating a new file doesn't trigger the auto-reloading logic. You can stop it by typing '''Ctrl-C''' ('''Ctrl-Break''' on Windows); then use the '''up''' arrow on your keyboard to find the command again, and hit enter.
=== Explore the free admin functionality ===
Now that we've registered Poll, Django knows that it should be displayed on the admin index page.
Click "Polls." Now you're at the "change list" page for polls. This page displays all the polls in the database and lets you choose one to change it. There's the "What's up?" poll we created in the first tutorial.
Things to note here:
* The form is automatically generated from the Poll model.
* The different model field types (DateTimeField, CharField) correspond to the appropriate HTML input widget. Each type of field knows how to display itself in the Django admin.
* Each DateTimeField gets free JavaScript shortcuts. Dates get a "Today" shortcut and calendar popup, and times get a "Now" shortcut and a convenient popup that lists commonly entered times.
The bottom part of the page gives you a couple of options:
* Save -- Saves changes and returns to the change-list page for this type of object.
* Save and continue editing -- Saves changes and reloads the admin page for this object.
* Save and add another -- Saves changes and loads a new, blank form for this type of object.
* Delete -- Displays a delete confirmation page.
Change the "Date published" by clicking the "Today" and "Now" shortcuts. Then click "Save and continue editing." Then click "History" in the upper right. You'll see a page listing all changes made to this object via the Django admin, with the timestamp and username of the person who made the change:
History page for poll object
=== Adding related objects ===
OK, we have our Poll admin page. But a Poll has multiple Choices, and the admin page doesn't display choices.
Yet.
There are two ways to solve this problem. The first is to register Choice with the admin just as we did with Poll. That's easy:
<pre>
from polls.models import Choice
admin.site.register(Choice)
</pre>
Now "Choices" is an available option in the Django admin. Check out the '''Add Choice''' form.
In that form, the "Poll" field is a select box containing every poll in the database. Django knows that a ForeignKey should be represented in the admin as a <select> box. In our case, only one poll exists at this point.
Also note the "Add Another" link next to "Poll." Every object with a ForeignKey relationship to another gets this for free. When you click "Add Another," you'll get a popup window with the "Add poll" form. If you add a poll in that window and click "Save," Django will save the poll to the database and dynamically add it as the selected choice on the "Add choice" form you're looking at.
But, really, this is an inefficient way of adding Choice objects to the system. It'd be better if you could add a bunch of Choices directly when you create the Poll object. Let's make that happen.
Remove the register() call for the Choice model. Then, edit the Poll registration code to read:
<pre>
class ChoiceInline(admin.StackedInline):
model = Choice
extra = 3
class PollAdmin(admin.ModelAdmin):
fieldsets = [
(None, {'fields': ['question']}),
('Date information', {'fields': ['pub_date'], 'classes': ['collapse']}),
]
inlines = [ChoiceInline]
admin.site.register(Poll, PollAdmin)
</pre>
This tells Django: "Choice objects are edited on the Poll admin page. By default, provide enough fields for 3 choices."
Load the "Add poll" page to see how that looks, you may need to restart your development server:
It works like this: There are three slots for related Choices -- as specified by extra -- and each time you come back to the "Change" page for an already-created object, you get another three extra slots.
=== Customize the admin change list ===
Now that the Poll admin page is looking good, let's make some tweaks to the admin "change list" page -- the one that displays all the polls in the system.
By default, Django displays the str() of each object. But sometimes it'd be more helpful if we could display individual fields. To do that, use the list_display admin option, which is a tuple of field names to display, as columns, on the change list page for the object:
<pre>
class PollAdmin(admin.ModelAdmin):
# ...
list_display = ('question', 'pub_date')
</pre>
Just for good measure, let's also include the was_published_today custom method from Tutorial 1:
<pre>
class PollAdmin(admin.ModelAdmin):
# ...
list_display = ('question', 'pub_date', 'was_published_today')
</pre>
Now, check out the polls list.
You can click on the column headers to sort by those values -- except in the case of the was_published_today header, because sorting by the output of an arbitrary method is not supported. Also note that the column header for was_published_today is, by default, the name of the method (with underscores replaced with spaces).
This is shaping up well. Let's add some search capability. Add this to '''class PollAdmin''':
class PollAdmin(admin.ModelAdmin):
# ...
search_fields = ['question']
That adds a search box at the top of the change list. When somebody enters search terms, Django will search the question field. You can use as many fields as you'd like -- although because it uses a LIKE query behind the scenes, keep it reasonable, to keep your database happy.
Finally, because Poll objects have dates, it'd be convenient to be able to drill down by date. Add this line:
class PollAdmin(admin.ModelAdmin):
# ...
date_hierarchy = 'pub_date'
That adds hierarchical navigation, by date, to the top of the change list page. At top level, it displays all available years. Then it drills down to months and, ultimately, days.
That's the basics of the Django admin interface!
Create a poll! Create some choices. Find your views, and show them to the world.
== Part 4.5: Deploy again, again! ==
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