Installing The Captcha

The captcha field I use is quite simple and effective. I originally got it from http://django.agami.at/media/captcha/, but the project seems to be unmaintained now. Along the road to Django 1.0, some changes were made to the way form fields work, and there is a minor change required in the base code for this captcha field if you want it to work. Alternatively, you can use a copy of the field that I'm currently using.

All you need to do is extract the captcha directory somewhere on your PYTHONPATH. The author recommends putting it in django.contrib, but I usually just place it straight on the PYTHONPATH so all I need to do is from captcha import CaptchaField instead of from django.contrib.captcha import CaptchaField. Minor details...

Adding The Captcha

The first thing you'll want to do after installing the captcha field is add the field itself to your comments form. Instead of subclassing the built-in django.contrib.comments.forms.CommentForm form, I simply decorated the constructor of the form as such:

1
2
3
4
5
6
7
8
9

from django.contrib.comments.forms import CommentForm
from captcha import CaptchaField

def add_captcha(func):
    def wrapped(self, *args, **kwargs):
        func(self, *args, **kwargs)
        self.fields['security_code'] = CaptchaField()
    return wrapped
CommentForm.__init__ = add_captcha(CommentForm.__init__)

This adds a field called security_code to the CommentForm, and it works the same way as if you had done something like this:

1
2
3
4
5
6
7

from django import forms
from captcha import CaptchaField

class MyCommentForm(forms.Form):
    name = forms.CharField()
    ...
    security_code = CaptchaField()

You can put the decorating snippet from above anywhere you'd like so long as the module you put it in is loaded at some point in your project. I usually put this sort of magic in my main urls.py file so it's harder to forget about when I debug things.

Fixing the Form

The first problem with this little trick seems to be that the CaptchaField is rendered as unsafe HTML in the default form.html template in the built-in comments application. That just means that, instead of seeing the captcha, you will see the HTML necessary to render the CaptchaField directly on the page, like this:

<input type="hidden" name="security_code" value="captcha.caZ1SqQ" />
<img src="/static/captchas/caZ1SqQ/0656f09d3974850397dd4c4974f23a35.gif"
 alt="" /><br /><input type="text" name="security_code"
 id="id_security_code" />

To fix that, you can apply the safe filter to the field and make the template look something like this:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

{% load comments i18n %}
<form action="{% comment_form_target %}" method="post">
<table>
{% for field in form %}
    {% if field.is_hidden %}
    {{ field }}
    {% else %}
    <tr{% ifequal field.name "honeypot" %} style="display:none;"{% endifequal %}>
        <th>{{ field.label_tag }}:</th>
        <td {% if field.errors %} class="error"{% endif %}>
            {{ field|safe }} &nbsp;
            {% if field.errors %}{{ field.errors|join:"; " }}{% endif %}
        </td>
    </tr>
    {% endif %}
{% endfor %}
</table>
<p class="submit">
    <input type="submit" name="post" class="submit-post"
     value="{% trans "Post" %}" />
    <input type="submit" name="preview" class="submit-preview"
     value="{% trans "Preview" %}" />

</form>

Notice the {{ field|safe }} in there. Also note that I prefer the table layout for the comment form over the default mode. If you change your form template as I have done, you should put the updated copy in your own project's template directory. It belongs in templates/comments/form.html, assuming that your templates directory is called templates. You'll probably also want to check out the preview.html template for the django.contrib.comments application. I changed mine to look like this:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23

{% extends "comments/base.html" %}
{% load i18n %}

{% block title %}{% trans "Preview your comment" %}{% endblock %}

{% block content %}
    {% load comments %}
    {% if form.errors %}
    <h1>{% blocktrans count form.errors|length as counter %}Please
     correct the error below{% plural %}Please correct the errors below
     {% endblocktrans %}</h1>
    {% else %}
    <h1>{% trans "Preview your comment" %}</h1>
        <blockquote>{{ comment|linebreaks }}</blockquote>

        {% trans "and" %} <input type="submit" name="submit"
         class="submit-post" value="{% trans "Post your comment" %}"
         id="submit" /> {% trans "or make changes" %}:

    {% endif %}

    {% include 'comments/form.html' %}
{% endblock %}

See how I just use the include tag to pull in the comments/form.html template I mentioned above? Saves a lot of typing and potential for problems... If you update the preview.html template, you should save your copy in templates/comments/preview.html, assuming your templates directory is called templates.

Testing It Out

At this point, you should be able to try out your newly installed captcha-fied comments. If it doesn't work, please comment on this article and perhaps we can figure out the problem!

Install Python

Site5 (and many other shared hosting providers that offer SSH access) already has Python installed, but you will want to have your own copy so you can install various tools without affecting other users. So go ahead and download virtual python:

mkdir ~/downloads
cd ~/downloads
wget http://peak.telecommunity.com/dist/virtual-python.py

Virtual Python will make a local copy of the installed Python in your home directory. Now you want to make sure you execute this next command with the newest version of Python available on your host. For example, Site5 offers both Python 2.3.4 and Python 2.4.3. We want to use Python 2.4.3. To verify the version of your Python, execute the following command:

python -V

If that displays Python 2.3.x or anything earlier, try using python2.4 -V or python2.5 -V instead. Whichever command renders the most recent version of Python is the one you should use in place of python in the next command. Since python -V currently displays Python 2.4.3 on my Site5 sandbox, I will execute the following command:

python ~/downloads/virtual-python.py

Again, this is just making a local copy of the Python installation that you used to run the virtual-python.py script. Your local installation is likely in ~/lib/python2.4/ (version could vary).

Make Your Local Python Be Default

To reduce confusion and hassle, let's give our new local installation of Python precedence over the system-wide Python. To do that, open up your ~/.bashrc and make sure it contains a line similar to this:

export PATH=$HOME/bin:$PATH

If you're unfamiliar with UNIX-based text editors such as vi, here is what you would type to use vi to make the appropriate changes:

• vi ~/.bashrc to edit the file
• go to the end of the file by using the down arrow key or the j key
• hit o (the letter) to tell vi you want to start typing stuff on the next line
• type export PATH=$HOME/bin:$PATH
• hit the escape key
• type :x to save the changes and quit. Don't forget the : at the beginning. Alternatively, you can type :wq, which works exactly the same as :x.

Once you've made the appropriate changes to ~/.bashrc, you need to make those changes take effect in your current SSH session:

source ~/.bashrc

Now we should verify that our changes actually took place. Type the following command:

which python

If they output of that command is not something like ~/bin/python or /home/[your username]/bin/python, something probably didn't work. If that's the case, you can try again, or simply remember to use ~/bin/python instead of python throughout the rest of this HOWTO.

Install Python's setuptools

Now we should install Python's setuptools to make our lives easier down the road.

cd ~/downloads
wget http://peak.telecommunity.com/dist/ez_setup.py
python ez_setup.py

This gives us access to a script called easy_install, which makes it easy to install many useful Python tools. We will use this a bit later.

Download Django

Let's now download the most recent development version of Django. SSH into your account and execute the following commands (all commands shall be executed on your host).

svn co http://code.djangoproject.com/svn/django/trunk ~/downloads/django-trunk

Now we should make a symlink (or shortcut) to Django and put it somewhere on the Python Path. A sure-fire place is your ~/lib/python2.4/site-packages/ directory (again, that location could vary from host to host):

ln -s ~/downloads/django-trunk/django ~/lib/python2.4/site-packages
ln -s ~/downloads/django-trunk/django/bin/django-admin.py ~/bin

Now verify that Django is installed and working by executing the following command:

python -c "import django; print django.get_version()"

That command should return something like 1.0-final-SVN-8964. If you got something like that, you're good to move onto the next section. If, however, you get something more along the lines of...

Traceback (most recent call last):
    File "<string>", line 1, in ?
ImportError: No module named django

...then your Django installation didn't work. If this is the case, make sure that you have a ~/downloads/django-trunk/django directory, and also verify that ~/lib/python2.4/site-packages actually exists.

Installing Dependencies

In order for your Django projects to become useful, we need to install some other packages: PIL (Python Imaging Library, required if you want to use Django's ImageField), MySQL-python (a MySQL database driver for Python), and flup (a utility for fastcgi-powered sites).

easy_install -f http://www.pythonware.com/products/pil/ Imaging
easy_install mysql-python
easy_install flup

Sometimes, using easy_install to install PIL doesn't go over too well because of your (lack of) permissions. To circumvent this situation, you can always download the actual PIL source code and install it manually.

cd ~/downloads
wget http://effbot.org/downloads/Imaging-1.1.6.tar.gz
tar zxf Imaging-1.1.6.tar.gz
cd Imaging-1.1.6
ln -s ~/downloads/Imaging-1.1.6/PIL ~/lib/python2.4/site-packages

And to verify, you can try this command:

python -c "import PIL"

If that doesn't return anything, you're good to go. If it says something about "ImportError: No module named PIL", it didn't work. In that case, you have to come up with some other way of installing PIL.

Setting Up A Django Project

Let's attempt to setup a sample Django project.

mkdir -p ~/projects/django
cd ~/projects/django
django-admin.py startproject mysite
cd mysite
mkdir media templates

If that works, then you should be good to do the rest of your Django development on your server. If not, make sure that ~/downloads/django-trunk/django/bin/django-admin.py exists and that it has a functioning symlink (shortcut) in ~/bin. If not, you'll have to make adjustments according to your setup. Your directory structure should look something like:

• projects
  • django
    • mysite
      • media
      • templates
      • __init__.py
      • manage.py
      • settings.py
      • urls.py

Making A Django Project Live

Now we need to make your Django project accessible from the Web. On Site5, I generally use either a subdomain or a brand new domain when setting up a Django project. If you plan on having other projects accessible on the same hosting account, I recommend you do the same. Let's assume you setup a subdomain such as mysite.mydomain.com. On Site5, you would go to ~/public_html/mysite for the next few commands. This could differ from host to host, so I won't go into much more detail than that.

Once you're in the proper place, you need to setup a few things: two symlinks, a django.fcgi, and a custom .htaccess file. Let's begin with the symlinks.

ln -s ~/projects/django/mysite/media ~/public_html/mysite/static
ln -s ~/lib/python2.4/site-packages/django/contrib/admin/media ~/public_html/mysite/media

This just makes it so you can have your media files (CSS, images, javascripts, etc) in a different location than in your public_html.

Now for the django.fcgi. This file is what tells the webserver to execute your Django project.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14

#!/home/[your username]/bin/python
import sys, os

# Add a custom Python path.
sys.path.insert(0, "/home/[your username]/projects/django")

# Switch to the directory of your project. (Optional.)
os.chdir("/home/[your username]/projects/django/mysite")

# Set the DJANGO_SETTINGS_MODULE environment variable.
os.environ['DJANGO_SETTINGS_MODULE'] = "mysite.settings"

from django.core.servers.fastcgi import runfastcgi
runfastcgi(method="threaded", daemonize="false")

And finally, the .htaccess file:

1
2
3
4
5
6

RewriteEngine On
RewriteBase /
RewriteRule ^(media/.*)$ - [L]
RewriteRule ^(static/.*)$ - [L]
RewriteCond %{REQUEST_URI} !(django.fcgi)
RewriteRule ^(.*)$ django.fcgi/$1 [L]

The .htaccess file makes it so that requests to http://mysite.mydomain.com/ are properly directed to your Django project. So, now you should have a directory structure that something that looks like this:

• public_html
  • mysite
    • media
    • static
    • .htaccess
    • django.fcgi

If that looks good, go ahead and make the django.fcgi executable and non-writable by others:

chmod 755 ~/public_html/mysite/django.fcgi

After that, head over to http://mysite.mydomain.com/ (obviously, replace the mydomain accordingly). If you see a page that says you've successfully setup your Django site, you're good to go!

Afterthoughts

I've noticed that I need to "restart" my Django sites on Site5 any time I change the .py files. There are a couple methods of doing this. One includes killing off all of your python processes (killall ~/bin/python) and the other simply updates the timestamp on your django.fcgi (touch ~/public_html/mysite/django.fcgi). I find the former to be more destructive and unreliable than the latter. So, my advice is to use the touch method unless it doesn't work, in which case you can try the killall method.

Good luck!

Create a Django Project

The first step is to create a Django project. If you already have a project that you can play with, you can skip this step. To create a project, go to a place where you want to keep your code (like C:\projects or /home/me/projects) in a command prompt/terminal and run the following command:

django-admin.py startproject myproject

This will create a new directory in your current location called myproject (you can replace myproject with whatever you'd like so long as you're consistent). This new directory will contain a few files:

• __init__.py
• manage.py
• settings.py
• urls.py

If you get an error message when running the above command, you might not have Django installed properly. See Step-by-Step: Installing Django for details on installing Django.

Create An Application

Once you have a Django project setup, you should create a new application.

Note: If you're using Windows, you will probably need to omit the ./ on the ./manage.py commands. I will include them here for everyone else who's using Linux or a Mac.

cd myproject
./manage.py startapp specialapp

This will create a new directory in your myproject directory. This new directory will contain three files: __init__.py, models.py, and views.py. We are only concerned with the models.py file in this article.

Create Your Models

Models are usually a direct representation of what your database will be. Django makes creating these models extremely easy, and Python's syntax makes them quite readable. The Django framework asks for models to be defined in the models.py file that was created in the last step. Here's an example (for my buddy who prompted the creation of this article):

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13

from django.db import models

class Component(models.Model):
    item_number = models.CharField(max_length=20)
    name = models.CharField(max_length=50)
    size = models.CharField(max_length=10)
    quantity = models.IntegerField(default=1)
    price = models.DecimalField(max_digits=8, decimal_places=2)

class Project(models.Model):
    name = models.CharField(max_length=50)
    components = models.ManyToManyField(Component)
    instructions = models.TextField()

(for more information about models, see the Django Model API Reference)

I don't know about you, but that code seems pretty straightforward to me. I'll spare you all the details about what's going on (that can be a future article).

Install Your New Application

Once you have your models setup, we need to add our specialapp to our list of INSTALLED_APPS in order for Django to register these models. To do that, open up settings.py in your myproject directory, go to the bottom of the file, until you see something like

1
2
3
4
5
6

INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
)

When you find that, add your specialapp to the list

1
2
3
4
5
6
7

INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
    'specialapp'
)

Setup Your Database

Now you need to let Django know what kind of database you're using. Django currently supports MySQL, SQLite3, PostgreSQL, and Oracle natively, but you can get third-party tools that allow you to use other database (like SQL Server).

Still in your settings.py, go to the top until you see DATABASE_ENGINE and DATABASE_NAME. Set that to whatever type of database you are using:

1
2

DATABASE_ENGINE = 'sqlite3'
DATABASE_NAME = 'myproject.db'

Save your settings.py and go back to your command prompt/terminal.

Get Django's Opinion For Your Schema

Make sure you're in your myproject directory and run the following command:

./manage.py sqlall specialapp

This command will examine the models that we created previously and will generate the appropriate SQL to create the tables for your particular database. For SQLite, we get something like this for output:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

BEGIN;
CREATE TABLE "specialapp_component" (
      "id" integer NOT NULL PRIMARY KEY,
      "item_number" varchar(20) NOT NULL,
      "name" varchar(50) NOT NULL,
      "size" varchar(10) NOT NULL,
      "quantity" integer NOT NULL,
      "price" decimal NOT NULL
)
;
CREATE TABLE "specialapp_project" (
      "id" integer NOT NULL PRIMARY KEY,
      "name" varchar(50) NOT NULL,
      "instructions" text NOT NULL
)
;
CREATE TABLE "specialapp_project_components" (
      "id" integer NOT NULL PRIMARY KEY,
      "project_id" integer NOT NULL REFERENCES "specialapp_project" ("id"),
      "component_id" integer NOT NULL REFERENCES "specialapp_component" ("id"),
      UNIQUE ("project_id", "component_id")
)
;
COMMIT;

Notice how Django does all sorts of nifty things, like wrapping the table creation queries in a transaction, setting up indexes, unique keys, and defining relationships between tables. The output also offers a solution to the original problem my buddy had: an intermediate table that just keeps track of relationships between projects and components (the specialapp_project_components table).

Notice that the SQL above may not work with database servers other than SQLite.

Enhancing The Intermediate Table

After my buddy reviewed this article, he asked a very interesting and valid question: What if a project needs 3 of one component? In response, I offer the following models (this requires a modern version of Django--it doesn't work on Django 0.96.1 or earlier):

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21

from django.db import models

class Component(models.Model):
    item_number = models.CharField(max_length=20)
    name = models.CharField(max_length=50)
    size = models.CharField(max_length=10)
    quantity = models.IntegerField(default=1)
    price = models.DecimalField(max_digits=8, decimal_places=2)

class Project(models.Model):
    name = models.CharField(max_length=50)
    components = models.ManyToManyField(Component, through='ProjectComponent')
    instructions = models.TextField()

class ProjectComponent(models.Model):
    project = models.ForeignKey(Project)
    component = models.ForeignKey(Component)
    quantity = models.PositiveIntegerField()

    class Meta:
        unique_together = ['project', 'component']

Running ./manage.py sqlall specialapp now generates the following SQL:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27

BEGIN;
CREATE TABLE "specialapp_component" (
    "id" integer NOT NULL PRIMARY KEY,
    "item_number" varchar(20) NOT NULL,
    "name" varchar(50) NOT NULL,
    "size" varchar(10) NOT NULL,
    "quantity" integer NOT NULL,
    "price" decimal NOT NULL
)
;
CREATE TABLE "specialapp_project" (
    "id" integer NOT NULL PRIMARY KEY,
    "name" varchar(50) NOT NULL,
    "instructions" text NOT NULL
)
;
CREATE TABLE "specialapp_projectcomponent" (
    "id" integer NOT NULL PRIMARY KEY,
    "project_id" integer NOT NULL REFERENCES "specialapp_project" ("id"),
    "component_id" integer NOT NULL REFERENCES "specialapp_component" ("id"),
    "quantity" integer unsigned NOT NULL,
    UNIQUE ("project_id", "component_id")
)
;
CREATE INDEX "specialapp_projectcomponent_project_id" ON "specialapp_projectcomponent" ("project_id");
CREATE INDEX "specialapp_projectcomponent_component_id" ON "specialapp_projectcomponent" ("component_id");
COMMIT;

As you can see, most of the SQL is the same. The main difference is that the specialapp_project_components table has become specialapp_projectcomponent and it now has a quantity column. This can be used to keep track of the quantity of each component that a project requires. You can add however many fields you want to this new intermediate table's model.

Using This SQL

There are several ways you can use the SQL generated by Django. If you want to make your life really easy, you can have Django create the tables for you directly. Assuming that you have specified all of the appropriate database information in your settings.py file, you can simply run the following command:

./manage.py syncdb

This will execute the queries generated earlier directly on your database, creating the tables (if they don't already exist). Please note that this command currently will not update your schema if the table exists but is missing a column or two. You must either do that manually or drop the table in question and then execute the syncdb command.

Another option, if you want to keep your DDL(Data Definition Language) in a separate script (maybe if you want to keep it in some sort of version control) is something like:

./manage.py sqlall specialapp > specialapp-ddl-080813.sql

This just puts the output of the sqlall command into a file called specialapp-ddl-080813.sql for later use.

Benefits of Using Django To Create Your Schema

• Simple: I personally find the syntax of Django models to be very simple and direct. There is a comprehensive API that explains and demonstrates what Django models are capable of.
• Fast: Being that the syntax is so simple, I find that it makes designing and defining your schema much faster than trying to do it with raw SQL or using a database administration GUI.
• Understandable: Looking at the model code in Django is not nearly as intimidating as similar solutions in other frameworks (think about Java Persistence API models).
• Intelligent: Using the same model code, Django can generate proper Data Definition Language SQL for several popular database servers. It handles indexes, keys, relationships, transactions, etc. and can tell the difference between server types.

Downfalls of Using Django To Create Your Schema

• The Table Prefix: Notice how all of the tables in the SQL above were prefixed with specialapp_. That's Django's safe way of making sure models from different applications in the same Django project do not interfere with each other. However, if you don't plan on using Django for your end project, the prefix could be a major annoyance. There are a couple solutions:
  • A simple "search and replace" before executing the SQL in your database
  • Define the db_table option in your models
• Another Technology: Django (or even Python) may or may not be in your organization's current development stack. If it's not, using the methods described in this article would just become one more thing to support.

Other Thoughts

I first thought about doing the things mentioned in this application when I was working on a personal Java application. I like to use JPA when developing database-backed applications in Java because it abstracts away a lot of the database operations. However, I don't like coming up with the model classes directly, so I usually reverse engineer them from existing database tables.

Before thinking about the things discussed in this article, I created the tables by hand, making several modifications to the schema before I was satisfied with my JPA models. This proved to be quite bothersome and time-consuming.

After using Django to develop my tables, the JPA models turned out to be a lot more reliable, and they were usually designed properly from the get-go. I haven't created tables manually ever since.

If you find yourself designing database schemas often, and you find that you have to make several changes to your tables before you/the project requirements are satisfied, you might consider using Django to do the grunt work. It's worked for me, and I'm sure it will work for you too.

Good luck!