In order to demonstrate Django’s rapid development potential, we will begin by constructing a simple, but fully-featured, e-commerce store. The goal is to be up and running with a product catalog and products for sale, including a simple payment processing interface, in about half-an-hour. If this seems ambitious, remember that Django offers a lot of built-in shortcuts for the most common web-related development tasks. We will be taking full advantage of these and there will be side discussions of their general use.
In addition to building our starter storefront, this article aims to demonstrate some other Django tools and techniques. In this article by Jesse Legg, author of Django 1.2 e-commerce, we will:
- Create our Django Product model to take advantage of the automatic admin tool
- Build a flexible but easy to use categorization system, to better organize our catalog of products
- Utilize Django’s generic view framework to expose a quick set of views on our catalog data
- Finally, create a simple template for selling products through the Google Checkout API
(Read more interesting articles on Django 1.2 e-commerce here.)
Before we begin, let’s take a moment to check our project setup. Our project layout includes two directories: one for files specific to our personal project (settings, URLs, and so on), and the other for our collection of e-commerce Python modules (coleman). This latter location is where the bulk of the code will live. If you have downloaded the source code from the Packt website, the contents of the archive download represents everything in this second location.
Designing a product catalog
The starting point of our e-commerce application is the product catalog. In the real world, businesses may produce multiple catalogs for mutually exclusive or overlapping subsets of their products. Some examples are: fall and spring catalogs, catalogs based on a genre or sub-category of product such as catalogs for differing kinds of music (for example, rock versus classical), and many other possibilities. In some cases a single catalog may suffice, but allowing for multiple catalogs is a simple enhancement that will add flexibility and robustness to our application.
As an example, we will imagine a fictitious food and beverage company, CranStore.com, that specializes in cranberry products: cranberry drinks, food, and desserts. In addition, to promote tourism at their cranberry bog, they sell numerous gift items, including t-shirts, hats, mouse pads, and the like. We will consider this business to illustrate examples as they relate to the online store we are building.
We will begin by defining a catalog model called Catalog. The basic model structure will look like this:
name = models.CharField(max_length=255
slug = models.SlugField(max_length=150)
publisher = models.CharField(max_length=300)
description = models.TextField()
pub_date = models.DateTimeField(default=datetime.now)
This is potentially the simplest model we will create. It contains only five, very simple fields. But it is a good starting point for a short discussion about Django model design. Notice that we have not included any relationships to other models here. For example, there is no products ManyToManyField. New Django developers tend to overlook simple design decisions such as the one shown previously, but the ramifications are quite important.
The first reason for this design is a purely practical one. Using Django’s built-in admin tool can be a pleasure or a burden, depending on the design of your models. If we were to include a products field in the Catalog design, it would be a ManyToManyField represented in the admin as an enormous multiple-select HTML widget. This is practically useless in cases where there could be thousands of possible selections.
If, instead, we attach a ForeignKey to Catalog on a Product model (which we will build shortly), we instantly increase the usability of Django’s automatic admin tool. Instead of a select-box where we must shift-click to choose multiple products, we have a much simpler HTML drop-down interface with significantly fewer choices. This should ultimately increase the usability of the admin for our users.
For example, CranStore.com sells lots of t-shirts during the fall when cranberries are ready to harvest and tourism spikes. They may wish to run a special catalog of touristy products on their website during this time. For the rest of the year, they sell a smaller selection of items online. The developers at CranStore create two catalogs: one is named Fall Collection and the other is called Standard Collection.
When creating product information, the marketing team can decide which catalog an individual product belongs to by simply selecting them from the product editing page. This is more intuitive than selecting individual products out of a giant list of all products from the catalog admin page.
Secondly, designing the Catalog model this way prevents potential “bloat” from creeping into our models. Imagine that CranStore decides to start printing paper versions of their catalogs and mailing them to a subscriber list. This would be a second potential ManyToManyField on our Catalog model, a field called subscribers. As you can see, this pattern could repeat with each new feature CranStore decides to implement.
By keeping models as simple as possible, we prevent all kinds of needless complexity. In addition we also adhere to a basic Django design principle, that of “loose coupling”. At the database level, the tables Django generates will be very similar regardless of where our ManyToManyField lives. Usually the only difference will be in the table name. Thus it generally makes more sense to focus on the practical aspects of Django model design. Django’s excellent reverse relationship feature also allows a great deal of flexibility when it comes time to using the ORM to access our data.
Model design is difficult and planning up-front can pay great dividends later. Ideally, we want to take advantage of the automatic, built-in features that make Django so great. The admin tool is a huge part of this. Anyone who has had to build a CRUD interface by hand so that non-developers can manage content should recognize the power of this feature. In many ways it is Django’s “killer app”.
Creating the product model
Finally, let’s implement our product model. We will start with a very basic set of fields that represent common and shared properties amongst all the products we’re likely to sell. Things like a picture of the item, its name, a short description, and pricing information.
name = models.CharField(max_length=300)
slug = models.SlugField(max_length=150)
description = models.TextField()
photo = models.ImageField(upload_to=’product_photo’,
manufacturer = models.CharField(max_length=300,
price_in_dollars = models.DecimalField(max_digits=6,
Most e-commerce applications will need to capture many additional details about their products. We will add the ability to create arbitrary sets of attributes and add them as details to our products later in this article. For now, let’s assume that these six fields are sufficient.
A few notes about this model: first, we have used a DecimalField to represent the product’s price. Django makes it relatively simple to implement a custom field and such a field may be appropriate here. But for now we’ll keep it simple and use a plain and built-in DecimalField to represent currency values.
Notice, too, the way we’re storing the manufacturer information as a plain CharField. Depending on your application, it may be beneficial to build a Manufacturer model and convert this field to a ForeignKey.
Lastly, you may have realized by now that there is no connection to a Catalog model, either by a ForeignKey or ManyToManyField. Earlier we discussed the placement of this field in terms of whether it belonged to the Catalog or in the Product model and decided, for several reasons, that the Product was the better place. We will be adding a ForeignKey to our Product model, but not directly to the Catalog. In order to support categorization of products within a catalog, we will be creating a new model in the next section and using that as the connection point for our products.