Author Archives: Tom de Simone

Content types and Django CMS

Screenshot of the new ENB website

The new ENB website

One of our latest projects to go live is a new website for the English National Ballet. Part of a major rebrand, we completely replaced their old PHP site with a new content-managed site powered by Django CMS.

Django CMS is very flexible, largely due to its minimalistic approach. It provides no page templates out of the box, so you can construct your HTML from the ground up. This is great if you want to make a CMS with a really strong design, because there is very little interference from the framework. However, its minimalistic approach also means that you sometimes have to write extra code to tie all the content together.

A good example of this is content types. In Django CMS, there is only one content type: Page. It has certain fields associated with it e.g. title, slug, published. Any other information that appears on a page comes courtesy of plugins. The default Django CMS plugins give you everything you need to add arbitrary text, images and video to a page. But what if you want more fields for your page? Let’s say, for example, you are representing a ballet production and you want category, thumbnail and summary text fields, which don’t appear on the page itself but are needed for listings elsewhere on the site?

We decided to create a special “metadata” plugin to be added to the production pages, that would only be visible to content editors and not end users. This was seen as the best solution that achieved our goal while maintaining a decent user experience for the editors.

The plugin model looks something like this:

class ProductionDetails(CMSPlugin):
    summary = models.CharField(max_length=200) # Short summary, shown in listings
    image = FilerImageField() # Thumbnail image, shown in listings
    audiences = models.ManyToManyField(Audience) # Categorisation

Note the use of django-filer for the image field. This is simply the best add-on I have encountered for dealing with image uploads and the inevitable cropping and resizing of said images. You can also use cmsplugin-filer (by the same author) to replace the standard image plugin that comes with Django CMS.

Now querying the database for, say, the first 10 productions for a family audience (audience id 3) is as simple as:

ProductionDetails.objects.filter(audiences=3, placeholder__page__published=True)[:10]

So now we have a plugin model that we can query, and we don’t need a template as we don’t want it to appear on the actual page, right? Wrong. We still want to provide a good user experience for the editors, and this includes looking at a page in edit mode and being able to tell whether the page already has the plugin or not. So we use request.toolbar.edit_mode in the template to decide whether to render the plugin:

{% load thumbnail %}

{% if request.toolbar.edit_mode %}
<div id="production-details">
 <img src="{% thumbnail instance.image 100x100 crop upscale subject_location=instance.image.subject_location %}" />
 <p>Summary: {{ instance.summary }}</p>
 <p>Audiences: {{ instance.audiences.all|join:', ' }}</p>
</div>
{% endif %}

Now this information will only appear if an editor has activated the inline editing mode while looking at the page. If they look at the page and the information is missing, they know they need to add the plugin!

This solution works quite well for us, although it is still fairly easy to create a page and forget to give it any metadata. Ideally it would be mandatory to add a metadata plugin. Perhaps the subject of a future blog post!

Running a Django (or any other) dev instance over HTTPS

Being able to run your dev instance over HTTPS is really useful: you might spot some weird bug that would have bitten you in production, and if you do find one, you can debug it much more easily. Googling for this subject resulted in several different tutorials using stunnel, but all of them broke in some way on my machine running Ubuntu Maverick. So here is how I got stunnel working – perhaps it will help someone else too:

sudo aptitude install stunnel
sudo su -
cd /etc
mkdir stunnel
cd stunnel
openssl req -new -x509 -days 365 -nodes -out stunnel.pem -keyout stunnel.pem
openssl gendh 2048 >> stunnel.pem
chmod 600 stunnel.pem
logout
cd

Now create a file called dev_https with the following text:

pid=
foreground=yes
debug = 7

[https]
accept=8443
connect=8000
TIMEOUTclose=1

Note: this assumes your web server is running on port 8000. If it’s not, change the value of “connect” to the appropriate port.

Finally, run:

sudo stunnel4 dev_https

Now if you go to https://localhost:8443/, you should see your HTTPS-enabled dev instance!

Note: To properly simulate a HTTPS connection in Django, you should also set an environment variable HTTPS=on. Without this, request.is_secure() will return False. You could set it at the same time as starting your dev instance e.g:

HTTPS=on python manage.py runserver

 

HTML5 input type=number and decimals/floats in Chrome

As you may already know, HTML5 has introduced a number of new input types, one of which is the “number” type. As you might expect, this is a form field which accepts numeric input. So what happens in Chrome with the following HTML when we try to enter a decimal (floating point) number and submit the form?

<input type="number" />

Answer: Chrome pops up a validation error:

Decimal number failing validation

So what’s going on here? Is it a bug? It doesn’t fail in Firefox.

Well actually it’s not a bug; the form field is behaving as defined by the W3C. Numeric input fields can take additional attributes “min” and “step”, which constrain the range of values allowed in your input. The “min” attribute is fairly obvious: it’s the minimum value your number can be. The “step” attribute is less intuitive: by playing with different values, you would most likely work out that it controls the increase/decrease when clicking the up/down buttons on the field. If you input the number 1 and click the up arrow, it will increase to 2. This is because the default step is 1. So far, so obvious. However, the step attribute also determines which values are valid, so a step of 1 means you can enter 1, 2, 3 etc. and a step of 2 means you can enter 2, 4, 6 etc, and when you click the up/down buttons the number will increase/decrease by 2 each time, but entering 3 or 5 in the box will cause a validation error. You can also use a decimal value: for example, a step of 0.3 will allow values such as 0.3, 0.6, 0.9 etc, but not 1 or 2.

But what if you want all the numbers to be valid, integers and decimals alike? In this case, set step to “any”:

<input type="number" step="any" />

Now you don’t get a validation error. Yay! Also note that if you only want to accept positive numbers, you’ll want to add min=”0″.

So the lesson here is that the “step” attribute is linked to both the up/down buttons and the range of values allowed in the field. When step=”any”, the up/down buttons will increase/decrease the number by 1. As far as I can tell, there is no way to have step=”any” and an increase/decrease of more (or less) than 1 when clicking the up/down buttons. Feel free to enlighten me in the comments though!