Thursday, January 28, 2010

Django and Ajax Form Submissions

I'm writing this post, in part, to correct a mistake. In Chapter 10 of the book, I cover how to add Ajax functionality to our Django e-commerce site by using the jQuery library. In the interest of keeping the chapter short and easy to understand, I kept the coverage in that chapter very rudimentary.

In hindsight, it was, I believe, a little too rudimentary, and I don't think the code is nearly as good as it could be. It's not very DRY (since we repeat ourselves), it's not degradable (if the user has JavaScript turned off, it doesn't work), and for larger forms with lots dozens of fields, it's likely to become a maintenance headache and possibly hurt performance.

This isn't errata, but it's worth taking another look at. Let's revisit how to do a simple Ajax form submission in a Django project with jQuery, using the submission of product reviews as an example.

(I'm assuming, if you're reading this, that you have the book handy and can follow along with what I'm doing. If you don't, I'll try to explain the concepts well enough so that you don't need the book. Just keep in mind there's a ProductReview model and associated form class being referenced here that I haven't included.)

Let's start with the URL entry that links to the view that accepts product review data, on page 219:

urlpatterns = patterns('ecomstore.catalog.views',
  ( r'^review/product/add/$', 'add_review' ),

One of the main problems is that this URL is defined here, and before, in our JavaScript code, we defined the same URL again, in perfect violation of the DRY principle. We're going to fix this. The first step is to give this URL entry a name parameter:

urlpatterns = patterns('ecomstore.catalog.views',
  ( r'^review/product/add/$', 'add_review', {}, 'product_add_review' ),

That means that, in our templates, we can use the URL tag and refer to 'product_add_review' to reference this URL. If it's in the template, we can make sure it's in the DOM someplace, and if it's in the DOM, then we can make our JavaScript code aware of it. That's exactly what we're going to do next.

In the book, on page 214, the fields are just text inputs on the page, and aren't actually contained in a form element. Actually, they're in a div element with an id attribute of 'review_form'. This is, at best, a missed opportunity.

Here's the new template code. Again, if you don't have the book, just know that 'review_form' is an instance of the review form class and that 'p' refers to the product instance on the current product page:

<div id="review_form">
<form id="review" action="{% url product_add_review %}" method="post">
  <div id="review_errors"></div>
    {{ review_form.as_table }}
    <tbody><tr><td colspan="2">
      <input id="id_slug" value="{{ p.slug }}" type="hidden">
      <input id="submit_review" value="Submit" type="submit">
      <a href="javascript:void(0);" id="cancel_review">Cancel</a>

With this, the DOM has all the semantic information it needs for posting a review form, and it can pass that along to our JavaScript. Also notice that I changed the "Cancel" button from a submit input to an anchor element.

Now, the changes we're going to make to our JavaScript are more than just a little superficial. If you're sitting there with the book in front of you, you won't be able to just change the addProductReview() function and have it work, because we're going to change the events that are fired and how we're attaching those events.

First, we're going to attach the addProductReview() to the form element. Inside of the prepareDocument() function, the contents of which are listed in the middle of page 216, remove this line:


and replace it with this:


Now, the addProductReview() function will fire whenever someone submits the form, which is done by click the "Submit" button.

Let's turn our attention to the addProductReview() function itself and give it an extreme makeover. In the book, we use the function to submit our Ajax request, but here, I'm going to use the jQuery.ajax() function, which allows for some more fine-grained control over the submission process. Here is the reworked version, which I will explain, line-by-line, in a moment:

function addProductReview(e){
  var review_form = jQuery(;
    url: review_form.attr('action'),
    type: review_form.attr('method'),
    data: review_form.serialize(),
    dataType: 'json',
    success: function(json){
      // code to update DOM here
    error: function(xhr, ajaxOptions, thrownError){
      // log ajax errors?

This new addProductReview() function takes a single argument, 'e', which refers to the form submission event itself, passed down on high from when we attached the function to the submit form event. 'e' allows us to do a couple of interesting things.

First, we call preventDefault() on the event. That means that the JavaScript will halt the normal form submission, so the browser won't reload the page. Naturally, if the user has JavaScript disabled in their browser, e.preventDefault won't fire, and the form will post to the "Add Review" URL as usual, the non-ajaxy way. This is the first step to ensure that our form degrades gracefully. (We'll revisit this is a moment, when we look at the view function.)

Next, we can reference the form element itself by using the selector and

var review_form = jQuery(;

'review_form' now refers to the 'form#review' element on the page, which includes all of its attributes and child elements, including the form inputs themselves. We're going to use this for the values we submit with our Ajax request.

The jQuery.ajax() function takes a few parameters. Here are the ones that I've used, along with a quick definition of each:

1. url - The URL path to which we should submit the request.
2. type - the HTTP method, either "get" or "post".
3. data - the form values, as a set of name-value pairs encoded in URL format. (e.g. "name=john&amp;content=good book!")
4. dataType - the type of data we expect as a response. (in this case, "json")
5. success - a function that handles the response after a successful request.
6. error - a function to handle unsuccessful requests. (optional)

The first three items, we get right from the form contents itself. The first two, we obtain by using the attr() function to get the values of the attributes of the form element:

url: review_form.attr('action'),
type: review_form.attr('method'),

The third one uses a new function that allows us to get the values of the form inputs as a set of name-value pairs, as a single URL string:

data: review_form.serialize()

That's much easier than having to spell out a selector and create a new variable for each input on the form, as was done in the book. This is especially true if you have a form with dozens of fields. The serialize() function is a handy shortcut. Also, DOM selection is an expensive operation for JavaScript, so doing a single selection of the form element and serializing it is much quicker than selecting the elements one-by-one, from a performance perspective.

For the last few items: we expect the dataType the server returns to be a JSON object. Inside of the success function, you can define the same code that was in the book, since the DOM update operations will be largely the same. Lastly, while we didn't create an architecture to handle Ajax errors in the book, I included the block where you would put code to handle any errors your Ajax request encounters. This could be useful for logging purposes.

Now that this is done, we just need to make a couple of small changes to our view function. First of all, requests that come into this URL from form submissions might be Ajax requests, or they could be coming from users who have JavaScript turned off and have just submitted a form the traditional, non-Ajax way. Our view function needs to check this and respond accordingly.

Here is the new view function in catalog/

def add_review(request):
if request.method == 'POST':
  form = ProductReviewForm(request.POST)
  slug = request.POST.get('slug')
  product =

  if form.is_valid():
    review =
    review.user = request.user
    review.product = product

    template = "catalog/product_review.html"
    html = render_to_string(template, {'review': review })
    response = simplejson.dumps({'success': 'True', 'html': html})

    html = form.errors.as_ul()
    response = simplejson.dumps({'success':'False', 'html':html})

  if request.is_ajax():
    return HttpResponse(response,
    return HttpResponseRedirect(product.get_absolute_url())

Again, I haven't defined the Review model or form in this case, but you should get the idea. We still handle the validation and saving of the new review instance in the same fashion. Towards the end, we just conditionalize the type of response we return depending on the nature of the request. If it's an Ajax request, we return the JSON object to the JavaScript function that we assume called it. Otherwise, it's a non-Ajax request coming from someone who has JavaScript disabled, and we just reload the current product page, with their new review posted.

They key here is in using request.is_ajax() to check the nature of the request. jQuery, as well as most other major JavaScript libraries, adds a header to the request called HTTP_X_REQUESTED_WITH with a value of "XMLHttpRequest". If Django finds this header in the request with that value, request.is_ajax() returns True.

There's one small problem with this: if a user has JavaScript turned off, and they submit a product review that doesn't validate, we don't communicate this to the user. They just get the page reloaded without their product review and no indication of what went wrong. In the case of our site, we already display a warning to people with JavaScript disabled that stuff might not work as expected. (Depending on your requirements, that might be unacceptable, but I leave it up to you, and the architecture of your own site, to determine how you could fix that particular bug.)

To recap, we've made the following improvements, which I encourage you to do elsewhere in your Django projects:

1. Give the Ajax request URL a name in your file, and use the {% url %} tag in the DOM of your page so jQuery can access it. (If the action attribute should be the current path, you can use {{ request.path }} in most cases in your templates to spell that out explicitly.)

2. Structure the elements of your page so they function all right even if the user has JavaScript disabled in their browser.

3. For forms, define the method for submission in the 'method' attribute of the form and use jQuery's attr() function to get it.

4. You can serialize the contents of a form for Ajax requests using the serialize() function on the form element.

5. In the view function, use the request.is_ajax() method to determine if the request came in via an Ajax request and, based on the origin, send the appropriate response.

As a side note, a lot of readers have complained about problems with the djangodblog app. For one, the installation instructions in the book don't work with current versions, but more importantly, it seems that if your database uses the UTF-8 character set encoding, django-db-log is not compatible with it. That's a bit disappointing, and I'm trying to figure out what to do about it.

Sunday, January 24, 2010

Money Isn't Everything In Branding

It really isn't. If it were, then you could launch any product and, given unlimited money, buy tons of TV ad time and you'd have a successful product on your hands. But that theory just doesn't make sense. In my household, when the television commercials come on, one of two things happen:

1. Everyone either tunes them out and goes back to pecking on their laptops, or

2. We start going MST3K on them, ridiculing them and interjecting our own snide and cynical comments into the inane little stories and dialogue.

Just about everyone I know is pretty good at ignoring commercials. My generation has evolved with a small part of the brain that knows how to ignore media when it's not relevant to us. There are a few that stand out amongst the dross, but most are just clutter and don't get stuck in my head. That means just buying TV ads and running them doesn't work anymore, which comes as no surprise.

Case in point: Dr. Pepper and Coca-Cola came out around the same time (around 1885), but were created by different companies. In 1972, the Coca-Cola company decided they would release a Dr. Pepper-esque clone, called Mr. Pibb, to try and take some of the market share away from Dr. Pepper. I don't have exact figures, but I rarely see Mr. Pibb in convenience stores and it's not very prominent in most grocery stores.

If money were the only thing that mattered, you'd think that a company like Coca-Cola, which has an annual advertising budget that could probably acquire an entire country, would be able to pose a significant threat to the Dr. Pepper brand. But we don't see Mr. Pibb many places other than in restaurants and diners on soda machines that the Coca-Cola company has dominated with its own line of beverages. Sure, it's still around, but Dr. Pepper clearly continues winning the battles in the marketplace.

When someone wants a Dr. Pepper, they immediately think of the name "Dr. Pepper". It's next to impossible for Coca-Cola to dislodge that name from people's minds to replace it with their own. It helps to get there first.

A more relevant, techno-geek example: take the new Bing search engine. Without question, at the time I'm writing this, Google is the largest and most frequently used search engine on the web. Its name has become synonymous with search. When people need to search on the web, they think "Google" and that's what they use. It's lodged in their brains.

Microsoft introduced Bing in mid-2009, a move clearly aimed to take some market share away from Google and Yahoo! In their ad campaigns, they show people who have used Google extensively for search babbling incoherent clanging like schizophrenic patients. They go on to suggest that "search overload" is something we should all be terrified of, and to avoid a similar fate, we should switch to using Bing.

This message seems a little odd to me, since there isn't any truth in it that resonates. It reminds me of the episode of the television show "Arrested Development" where the character Gob Bleuth opens a banana stand right next to his brother's banana stand to compete with them, and their slogan is "A frozen banana that won't make you sick and kill you". It's mudslinging without any truth to the message, and it's easy for the mind to ignore what it can easily discredit.

Moreover, Microsoft has pushed hard to brand Bing as a "decision engine" instead of a mere "search engine". I suppose this is their means of differentiating Bing from Google, but that's like trying to sell a "pop machine" to compete with a "soda machine". When you go to the Bing homepage, it seems just like Google, with a few small differences. It hardly seems like enough to convince people that they should switch over to using Bing instead of Google.

That's not to say Bing will wither and die completely. People are using it, but they're probably never going to be handling the majority of web searches. If that's Microsoft's goal, then they're out of their minds. Google is the Dr. Pepper and they're Mr. Pibb.

An important corollary of that is the fact that Google is currently working to develop its own Chrome operating system, which will be open source and available as an alternative to Windows. Spokespeople for Google have stated that they have no intention of trying to use Chrome to replace Windows as the most common OS.

Positioning tactics are everywhere. The other day I saw a bar of chocolate that said "Chocolate for wine lovers." People drinking wine can easily buy a Hershey's bar, but the company is trying to sneak their own chocolate into the mind of wine drinkers. Does chocolate even go with wine? Who knows? Maybe they'll put the idea in people's heads by putting it out there. (Problem is, I don't remember the name of the brand of chocolate. Fail.)

There's a very good book on the subject of positioning, called (aptly enough) Positioning, that covers this topic very well. It was written over thirty years ago, but the book is a very good overview of modern marketing, full of examples, and is very well written. If you're accustomed to reading long and dense computer books, you can probably finish the book in a few hours. If you're planning to start your own Internet company and don't know anything about branding, I'd say reading the book is well worth your time and money.

The important takeaway here is that money is definitely not everything. If you're a small business owner or just planning to start your own niche e-commerce site, that's great news, because it means there's a good chance you can achieve success without spending a whole lot of money on advertising. If you're selling a new product in a new market space, you'll probably have an easy time getting customers, provided you're selling something that people want to buy and your site seems trustworthy in appearance.

If you're entering an existing market with established competition, you'll have a much easier time if you position yourself relative to your competitors. I did it when I wrote my book on Django. I wanted to write an introductory book that covered the framework, but of course, there are plenty of "Introduction to Django" titles. Choosing to go the e-commerce route was my way of finding an untapped niche and distinguishing my book from others.

In following the "Modern Musician" example in the book, imagine that you want to sell musical instruments and other accessories online. I would first look at who the big players are. In terms of online merchants catering to musicians, Guitar Center and Musician's Friend are two big ones that show up on Google. They're also probably first in line in the mind of our prospects (customers) when they feel the urge to go buy guitar strings, capos, etc.

Now, Guitar Center and the other big players seem to make a strong effort to cater to everyone, no matter what they might need. For Modern Musician, that's probably not a good strategy. Let's start much smaller. These days, with RockBand on Macs and lots of other PC software recording programs, lots of musicians are doing home recording. Perhaps it would make sense to try and brand Modern Musician as an online merchant that supplies instruments to those musicians who have studios in their basements and garages. The slogan could be "The go-to place for DIY home studio recording."

By itself, of course, that's not a very great idea, the slogan's bad, and I'm sure it's being done by someone at the moment. But the hope is that you can find a hole in the minds of your customers, and that your brand can fill it. Give people a reason to think of your name when they are thinking about playing, writing, or recording music. Help them feel your store is helping them self-actualize their aspirations and dreams of being a musician. Remind them of the thrill of performing live or connecting with a raving fan of their music.

Naturally, whatever you promise, just make sure you can follow through on it and that it resonates with the truth. Otherwise, it's no better than the Bing commercials and, unlike Microsoft, you probably can't afford to fail.

Of course, if you happen to have a massive advertising budget and want to spend it on television commercials and billboards, by all means, do that. But I think that no matter how much money you have, creative strategy and careful planning are the most important assets in the marketing department. If you don't have those, there's a good chance that when your commercial airs on TV, me and everyone else will be ignoring it.