Matthew Daly's Blog

I'm a web developer in Norfolk. This is my blog...

13th August 2012 7:54 pm

Falling Back to Local Copies of Jquery and Jquery Mobile

I use jQuery Mobile a lot at work, and it’s brilliant. For quickly knocking together a high-quality user interface that works well on mobile devices, it’s unbeatable.

Like many web developers, I favour using a CDN-hosted version of both jQuery and jQuery Mobile, because it makes it more likely that the user won’t have to download the appropriate files as their web browser has already cached them. However, by doing this you run the risk of your site being negatively affected if the CDN provider goes down for any length of time. So, I think it’s a good idea to have a fallback for both jQuery and jQuery Mobile.

I spent a while looking and finally managed to come up with a solution that works well, and borrows heavily from a similar solution for jQuery UI by Tim James. First of all, load the stylesheets and JavaScript files as usual:

<link rel="stylesheet" href="http://code.jquery.com/mobile/1.1.1/jquery.mobile.structure-1.1.1.min.css" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script src="http://code.jquery.com/mobile/1.1.1/jquery.mobile-1.1.1.min.js"></script>

Below this, place the following inside another set of script tags:

if (typeof jQuery == 'undefined')
{
document.write(unescape("%3Cscript src='http://path-to-jquery.min.js' type='text/javascript'%3E%3C/script%3E"));
}

If jQuery is not defined, this will write another set of script tags that will load the local copy of jQuery. Now, inside a second set of script tags, place the following code:

if(typeof $.mobile == 'undefined')
{
document.write(unescape("%3Cscript src='http://path-to-jquery-mobile.min.js' type='text/javascript'%3E%3C/script%3E"));
}
$(function() {
if($('.ui-helper-hidden:first').is(':visible') === true){
$('<link rel="stylesheet" type="text/css" href="http://path-to-jquery-mobile-structure.min.css" />').appendTo('head');
}
});

This won’t work if it’s placed in the same set of script tags as the code above, because it requires that jQuery be working already. The first part works similarly to the jQuery fallback - if jQuery Mobile is not defined, it writes a new script tag. The second relies on an element in the DOM with a class of ui-helper-hidden, which jQuery Mobile would hide by default if it were loaded. If it is visible, the jQuery Mobile structure CSS file has not been loaded and so a link to the local copy of the stylesheet is created. Of course, this means you have to create this element, so add the following code to the very top of the body, directly under the opening body tag:

<div class='ui-helper-hidden'></div>

If you download copies of the appropriate files and set the paths to them correctly, you should now be able to enjoy all the advantages of using a CDN for hosting jQuery and jQuery Mobile while also having the security of knowing that if the CDN goes down, your application will still work fine. Exactly the same approach will work with jQuery UI as well.

31st May 2012 9:25 pm

Dumping Wordpress for Octopress

Lately I’ve gotten more and more fed up with WordPress as a blogging platform. It’s certainly a great content management system, and for non-technical bloggers it’s absolutely perfect, but I’ve been increasingly finding myself hitting barriers that make it harder than it should be to get stuff done. It’s just not the best platform for blogging about web development.

Take my recent series of Django tutorials, for example. You wouldn’t believe the amount of time I spent trying to format some of the code properly in TinyMCE for those. Furthermore, the end result, even though the theme was a custom one I’d built myself that was somewhat optimised for showing off code, wasn’t exactly great.

In my opinion, Markdown is a far better option for writing blog posts in than using a rich text editor like TinyMCE. You normally have a pretty good idea what the end results will look like, and it’s generally well-formatted HTML. Also, it means I can easily write my blog posts in Vim.

Octopress was therefore an obvious choice. It’s absolutely brilliant for sharing code - compared to WordPress, code samples look stunning. Also, because it generates static HTML, it loads an awful lot faster than WordPress does, and the default theme is extremely nice. So that’s what I’ve gone for.

The only issue is that my web host are a bit funny about offering SSH access, so I’ve resorted to FTP-ing the files across, which isn’t ideal. Still, it’s not that big an issue, and I’ll have to see how it goes with Octopress. I do have a low-end VPS I could point this domain name at instead and run it from there if necessary, so I can always resort to that if this is too cumbersome.

23rd April 2012 9:55 pm

Yet Another Tutorial for Building a Blog Using Python and Django - Part 5

In this instalment I’ll be showing you how we can make our blogging engine a little nicer to look at by adding some CSS and images, as well as expanding on Django’s templating system.

First of all, let’s add some CSS to our blog. When developing a web app with Django, you should place static files such as stylesheets and images in a folder inside your app (not project) folder called static. My project is called DjangoBlog, and my app is called blogengine, so all my static content should go in DjangoBlog/blogengine/static/. Here’s the stylesheet, which I’ve saved as style.css:

body {
background-color: #f0f0f0;
font-family: Arial, Helvetica, sans-serif;
}
#main {
width: 800px;
height: 100%;
margin: 50px auto;
}
ul#pageList {
margin: 0px;
padding: 10px 0px 10px 0px;
}
ul#pageList li {
display: inline;
margin-right: 10px;
font-size: 18px;
}
.post, .page {
width: 600px;
padding: 20px;
margin-bottom: 20px;
background-color: #ffffff;
}

In the same folder, I have a PNG icon for an RSS feed, and if you had some JavaScript files you wanted to use (such as a copy of jQuery), you would put them here too. Note that there’s nothing to stop you creating subfolders within /static, and in fact I would recommend you do so for any future project so you can separate out images, CSS and JavaScript easily.

With that done, we now need to change our templates to make use of this CSS. Here’s what header.html should look like:

<html>
<head>
<title>My Django Blog</title>
<link rel="stylesheet" type="text/css" href="/static/style.css" />
</head>
<body>
<div id="main">
<h1>My Django Blog</h1>
<a href="/feeds/posts/"><img src="/static/rss.png" width="50px" height="50px"></a>
<ul id="pageList">
<li><a href="/">Home</a></li>
{% load flatpages %}
{% get_flatpages as flatpages %}
{% for flatpage in flatpages %}
<li><a href="{{ flatpage.url }}">{{ flatpage.title }}</a></li>
{% endfor %}
</ul>

Next, here’s footer.html:

</div>
</body>
</html>

Now here’s category.html:

{% include 'header.html' %}
{% load comments %}
<h1>Posts for {{ category.title }}</h1>
{% if posts %}
{% for post in posts %}
<div class="post">
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
{{ post.text }}
{% get_comment_count for post as comment_count %}
<h3>Comments: {{ comment_count }}</h3>
</div>
{% endfor %}
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
{% else %}
<div class="post">
<p>No posts matched</p>
</div>
{% endif %}
{% include 'footer.html' %}

Then, posts.html:

{% include 'header.html' %}
{% load comments %}
{% if posts %}
{% for post in posts %}
<div class="post">
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
{{ post.text }}
{% get_comment_count for post as comment_count %}
<h3>Comments: {{ comment_count }}</h3>
</div>
{% endfor %}
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
{% else %}
<div class="post">
<p>No posts matched</p>
</div>
{% endif %}
{% include 'footer.html' %}

Here’s single.html:

{% include 'header.html' %}
{% load comments %}
{% for post in posts %}
<div class="post">
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
<h3>{{ post.pub_date }}</h3>
{{ post.text }}
<h3>By {{ post.author.first_name }} {{ post.author.last_name }}</h3>
<h3>Categories: {% for category in post.categories.all %} {{ category.title }} {% endfor %}</h3>
{% get_comment_count for post as comment_count %}
<h3>Comments: {{ comment_count }}</h3>
<ol>
{% get_comment_list for post as comments %}
{% for comment in comments %}
<li>{{ comment }}</li>
</ol>
{% endfor %}
{% render_comment_form for post %}
{% endfor %}
</div>
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
{% include 'footer.html' %}

And finally, flatpages/default.html:

{% include 'header.html' %}
<div class="page">
<h1>{{ flatpage.title }}</h1>
{{ flatpage.content }}
</div>
{% include 'footer.html' %}

Phew! There’s quite a lot there, so you may wish to grab these files from the GitHub repository rather than enter them yourself.

Now, all of the references to the CSS or image file need to refer to the /static folder under the root of the web server. Here’s the reference to our stylesheet:

<link rel="stylesheet" type="text/css" href="/static/style.css" />

And here’s where we get the image:

<a href="/feeds/posts/"><img src="/static/rss.png" width="50px" height="50px"></a>

All of our static files can be referenced via the /static folder by default, without needing to set up a rule to cover them in urls.py.

One other point worth noting is that we’ve added some code to the header to display links to all of the flat pages. This particular snippet of code in header.html is noteworthy:

{% load flatpages %}
{% get_flatpages as flatpages %}
{% for flatpage in flatpages %}
<li><a href="{{ flatpage.url }}">{{ flatpage.title }}</a></li>
{% endfor %}

Here, we first of all load the flat pages. Then we retrieve them, and loop through each of them. For each page, we create a new list item containing a link to the flat page, with the text being the flat page’s title. Note that we’re just referring to each flatpage object’s attributes here. Then we end the for loop.

The only problem with this is that all of the pages except the flat pages are handled by the blogengine application, not the flatpages one, so we can’t get the values for the flat pages, so we need to amend blogengine/views.py. Open it and add the following line near the top:

from django.contrib.flatpages.models import FlatPage

Now, nowhere else in the view is the FlatPage application needed, but it’s required in the template, so by importing it here we make it available in the template.

With that done, our Django-powered blog is beginning to look a bit more presentable, so I’ll leave it to you to style it however you wish, using this as a starting point. The blog is now pretty much feature-complete, however there’s one more thing I’d like to demonstrate before we finish up, namely generic views.

As you may have gathered by now, Django uses slightly different terminology to many other web development frameworks. Although it can be considered an MVC (Model-View-Controller) framework like many others, it’s generally referred to as an MTV (Model-Template-View) framework, with views containing the logic needed to present the data. While Django ships with a number of built-in applications to do certain repetitive tasks easily, not every task lends itself well to being handled by one generic application. However, these tasks may still require something similar be implemented over and over again, and that’s what generic views are for.

We don’t yet have a list of all of the available categories, so let’s use a generic view to do that. In urls.py, add the following lines at the top:

from django.views.generic import ListView
from blogengine.models import Category

Then, add the following lines at the top of the section for categories:

url(r'^categories/?$', ListView.as_view(
model=Category,
)),

Then, go into your templates folder and create a new folder in there called blogengine (or whatever you’re calling your blog application). In there, create a new file called category_list.html and enter the following code in it:

{% include 'header.html' %}
{% for category in object_list %}
<h3>{{ category.title }}</h3>
<p>{{ category.description }}</p>
{% endfor %}
{% include 'footer.html' %}

Now, ensure the development server is running, and go to http://127.0.0.1:8000/categories/, and you should see a list of your categories.

Now, you didn’t write a view for this at all. Instead, this is handled by a generic view. In urls.py, we imported the ListView generic view, which is nothing more than a list of objects. We then import the Category model. Then, we define a URLconf that maps the categories/ url to ListView, which displays a list of all the Category objects. The template used is determined automatically, and we create that template as normal. Note that in the template we refer to object_list - this demonstrates that we’re referring to the objects passed through generically, and in theory this same template could display any objects with attributes called title and description.

Now, it probably won’t have escaped your notice that a blog is effectively a list of posts, so can’t we use a generic view to display them? Well, yes we can! So why don’t we cut down on the amount of code we need to maintain and use a generic view, rather than writing our own view?

Go into blogengine/views.py and delete the getPosts function in its entirety. Next, go into urls.py and delete the part that deals with showing the posts (the two lines just under the Home page comment), and replace them with this:

url(r'^(?P<page>\d+)?/?$', ListView.as_view(
model=Post,
paginate_by=5,
)),

Note here that we specify how many items we paginate by. The ListView generic view supports pagination, making it ideally suited for any list of objects that may be spread across multiple pages - you just import the model you want and pass it through in the model parameter.

We also need to import the Post object in urls.py. Amend the line where you imported the Category model as follows:

from blogengine.models import Category, Post

Then move posts.html into your templates/blogengine folder and rename it post_list.html, then amend it to look like the following:

{% include 'header.html' %}
{% load comments %}
{% if object_list %}
{% for post in object_list %}
<div class="post">
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
{{ post.text }}
{% get_comment_count for post as comment_count %}
<h3>Comments: {{ comment_count }}</h3>
</div>
{% endfor %}
<br />
{% if page_obj.has_previous %}
<a href="/{{ page_obj.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page_obj.has_next %}
<a href="/{{ page_obj.next_page_number }}/">Next Page</a>
{% endif %}
{% else %}
<div class="post">
<p>No posts matched</p>
</div>
{% endif %}
{% include 'footer.html' %}

The changes here are minimal, just adjusting the names of objects to what the generic view uses. Now, if you refresh the browser, you should be able to see your blog posts, only now they’re being handled by Django’s ListView generic view. But they’re in the wrong order, so go into blogengine/models.py and add this code to the Post model:

class Meta:
ordering = ["-pub_date"]

This defines the order the Post objects should be in the model, rather than the view. If you now refresh the browser, they should be in the right order.

A ListView is only one of the generic views available in Django. There are others that are useful under other circumstances, but they’re beyond the scope of this tutorial, so I suggest that if you’re interested, you take the time to learn more about them on your own. They can save you a lot of time and effort if used well.

Sadly, that brings this series of tutorials to an end. I hope you’ve enjoyed learning about Django, and I hope you’ll be inspired to build something cool with it! As always, the code is available on GitHub, so feel free to download it, use it as the basis for your own projects, or whatever else you’d like to do with it.

29th March 2012 9:29 pm

Yet Another Tutorial for Building a Blog Using Python and Django - Part 4

Welcome back! In this tutorial we’ll continue extending our Django-powered blogging engine. We’ll add the capability to assign blog posts to categories, and comment on posts. We’ll also generate an RSS feed for our blog posts.

Categories are somewhat tougher to implement than most of what we’ve done beforehand. One category can be assigned to many blog posts, and many categories can be assigned to one blog post, so this relationship is described as a “many to many relationship” when drawing up the database structure. What it means is that you can’t directly map categories onto posts and vice versa - you have to create an intermediate database table for the relationship between posts and categories.

Here’s what your models.py should look like:

from django.db import models
from django.contrib.auth.models import User
# Create your models here.
class Category(models.Model):
title = models.CharField(max_length=200)
slug = models.SlugField(max_length=40, unique=True)
description = models.TextField()
class Meta:
verbose_name_plural = "Categories"
def __unicode__(self):
return self.title
def get_absolute_url(self):
return "/categories/%s/" % self.slug
class Post(models.Model):
title = models.CharField(max_length=200)
pub_date = models.DateTimeField()
text = models.TextField()
slug = models.SlugField(max_length=40, unique=True)
author = models.ForeignKey(User)
categories = models.ManyToManyField(Category, blank=True, null=True, through='CategoryToPost')
def __unicode__(self):
return self.title
def get_absolute_url(self):
return "/%s/%s/%s/" % (self.pub_date.year, self.pub_date.month, self.slug)
class CategoryToPost(models.Model):
post = models.ForeignKey(Post)
category = models.ForeignKey(Category)

We’re adding quite a bit of new code here. First of all we’re defining a new model called Category. Each category has a title, a description, and a slug (so we can have a dedicated page for each category). As usual, we define methods for unicode and get_absolute_url, but also note the class Meta. Here we’re defining some metadata for the class (ie, data about the data). The only thing we do here is essentially telling the admin interface that the plural of Category is not “Categorys” but “Categories”.

Then, in Post we add an additional field called Category, which we define as a ManyToManyField. Note the parameters passed through - we’re saying here that a post need not be assigned a category, and that CategoryToPost should be used as an intermediate table to link posts to categories.

Finally, we define the aforementioned CategoryToPost model, which has two fields, post and category. Both of these are foreign keys, mapping to a blog post and a category respectively. By creating entries in this table, a link can be created between a post and a category.

With our model changed, it’s time to update our admin.py as well:

import models
from django.contrib import admin
from django.contrib.auth.models import User
class CategoryAdmin(admin.ModelAdmin):
prepopulated_fields = {"slug": ("title",)}
class CategoryToPostInline(admin.TabularInline):
model = models.CategoryToPost
extra = 1
class PostAdmin(admin.ModelAdmin):
prepopulated_fields = {"slug": ("title",)}
exclude = ('author',)
inlines = [CategoryToPostInline]
def save_model(self, request, obj, form, change):
obj.author = request.user
obj.save()
admin.site.register(models.Post, PostAdmin)
admin.site.register(models.Category, CategoryAdmin)

Here we define a new class called CategoryAdmin, which details how we’re changing the admin interface for Category from the defaults generated from the fields provided. The only change we make here is that we prepopulate the slug field from the title, much like we did with blog posts.

Next, we define an inline for the relationships between categories and post, called CategoryToPostInline. This is a new concept - essentially it means that the category to post relationships can be defined in another model’s admin interface. We define the model this applies to, and that by default we will only add one additional field for adding categories when writing or editing a post (though users can add as many as they wish, or none). Note that the model this is based on is admin.TabularInline - this represents a tabular layout. If you prefer, you can use an alternative layout by using StackedInline instead.

Then, in PostAdmin we add our newly declared CategoryToPostInline to the PostAdmin class as an inline. Finally, at the bottom we register Category with the admin interface, so we can create and manage categories easily.

With that done, it’s time to edit our views.py:

# Create your views here.
from django.shortcuts import render_to_response
from django.core.paginator import Paginator, EmptyPage
from blogengine.models import Post, Category
def getPosts(request, selected_page=1):
# Get all blog posts
posts = Post.objects.all().order_by('-pub_date')
# Add pagination
pages = Paginator(posts, 5)
# Get the specified page
try:
returned_page = pages.page(selected_page)
except EmptyPage:
returned_page = pages.page(pages.num_pages)
# Display all the posts
return render_to_response('posts.html', { 'posts':returned_page.object_list, 'page':returned_page})
def getPost(request, postSlug):
# Get specified post
post = Post.objects.filter(slug=postSlug)
# Display specified post
return render_to_response('single.html', { 'posts':post})
def getCategory(request, categorySlug, selected_page=1):
# Get specified category
posts = Post.objects.all().order_by('-pub_date')
category_posts = []
for post in posts:
if post.categories.filter(slug=categorySlug):
category_posts.append(post)
# Add pagination
pages = Paginator(category_posts, 5)
# Get the category
category = Category.objects.filter(slug=categorySlug)[0]
# Get the specified page
try:
returned_page = pages.page(selected_page)
except EmptyPage:
returned_page = pages.page(pages.num_pages)
# Display all the posts
return render_to_response('category.html', { 'posts': returned_page.object_list, 'page': returned_page, 'category': category})

Here we import the Category model as well as the Post model. Then, the only additional change we need to make is to add a brand new getCategory view function. Note that this is quite similar to the getPosts function - we set up pagination in the same way, and rather than get all the posts, we get just those in the specified category. Also note that we’re using the template category.html rather than posts.html here, and we pass through category as well as posts and page when we return the render_to_response.

The next change we need to make is adding category.html. Go into your template directory and save the code below as category.html:

{% include 'header.html' %}
<h1>Posts for {{ category.title }}</h1>
{% if posts %}
{% for post in posts %}
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
{{ post.text }}
{% endfor %}
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
{% else %}
<p>No posts matched</p>
{% endif %}
{% include 'footer.html' %}

With our template in place, the last step is to add an appropriate URLconf. Edit urls.py to look like this:

from django.conf.urls.defaults import patterns, include, url
# Uncomment the next two lines to enable the admin:
from django.contrib import admin
admin.autodiscover()
urlpatterns = patterns('',
# Examples:
# url(r'^$', 'blog.views.home', name='home'),
# url(r'^blog/', include('blog.foo.urls')),
# Uncomment the admin/doc line below to enable admin documentation:
# url(r'^admin/doc/', include('django.contrib.admindocs.urls')),
# Uncomment the next line to enable the admin:
url(r'^admin/', include(admin.site.urls)),
# Home page
url(r'^$', 'blogengine.views.getPosts'),
url(r'^(?P<selected_page>\d+)/?$', 'blogengine.views.getPosts'),
# Blog posts
url(r'^\d{4}/\d{1,2}/(?P[-a-zA-Z0-9]+)/?$', 'blogengine.views.getPost'),
# Categories
url(r'^categories/(?P<categorySlug>\w+)/?$', 'blogengine.views.getCategory'),
url(r'^categories/(?P<categorySlug>\w+)/(?P<selected_page>\d+)/?$', 'blogengine.views.getCategory'),
# Flat pages
url(r'', include('django.contrib.flatpages.urls')),
)

Now, if you run python manage.py syncdb again, the category system should be up and running.

The next step is to add the facility to handle comments. Again, Django has its own application built in for handling comments, so go into setings.py and enter the following under INSTALLED_APPS:

     'django.contrib.comments',

Then run python manage.py syncdb again to generate the appropriate database tables. You’ll also need to amend urls.py to provide a dedicated URL for comments:

# Comments
url(r'^comments/', include('django.contrib.comments.urls')),

Place this before the URLconf for the flat pages.

Comments can be attached to any type of content, but we only want to attach them to blog posts, and they should only be visible in the single post template. But first of all, let’s add a comment count to posts in posts.html and category.html. Replace posts.html with this:

{% include 'header.html' %}
{% load comments %}
{% if posts %}
{% for post in posts %}
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
{{ post.text }}
{% get_comment_count for post as comment_count %}
<h3>Comments: {{ comment_count }}</h3>
{% endfor %}
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
{% else %}
<p>No posts matched</p>
{% endif %}
{% include 'footer.html' %}

And replace category.html with this:

{% include 'header.html' %}
{% load comments %}
<h1>Posts for {{ category.title }}</h1>
{% if posts %}
{% for post in posts %}
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
{{ post.text }}
{% get_comment_count for post as comment_count %}
<h3>Comments: {{ comment_count }}</h3>
{% endfor %}
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
{% else %}
<p>No posts matched</p>
{% endif %}
{% include 'footer.html' %}

The only significant changes here are that at the top we load comments, and underneath the post text we get the comment count for each post as the variable comment_count, then we display it underneath.

Now, we want to go further with our single post template. As well as a comment count, we want to add the actual comments themselves. Finally, we need a form for adding comments - in theory you can use the admin interface for doing this, but it’s very unlikely you’d want to do so. Open up single.html and edit it to look like this:

{% include 'header.html' %}
{% load comments %}
{% for post in posts %}
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
<h3>{{ post.pub_date }}</h3>
{{ post.text }}
<h3>By {{ post.author.first_name }} {{ post.author.last_name }}</h3>
<h3>Categories: {% for category in post.categories.all %} {{ category.title }} {% endfor %}</h3>
{% get_comment_count for post as comment_count %}
<h3>Comments: {{ comment_count }}</h3>
<ol>
{% get_comment_list for post as comments %}
{% for comment in comments %}
<li>{{ comment }}</li>
{% endfor %}
</ol>
{% render_comment_form for post %}
{% endfor %}
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
{% include 'footer.html' %}

This includes the same changes as the other two templates, so we load comments and display the comment count. Afterwards, we get the comment list for this post as comments, and then loop through the comments, showing them in an ordered list. Afterwards, we then use render_comment_form to show the default comment form for this post. If you’d prefer to create your own comment form, you can use get_comment_form instead to get a form object you can use in the template.

You’ll also need to make some minor changes to the view to get the form working. Save single.html and open blogengine/views.py and add the following line of code to your import statements:

from django.template import RequestContext

Then, amend the final line of the getPost function as follows:

    return render_to_response('single.html', { 'posts':post}, context_instance=RequestContext(request))

The reason this needs to be changed is that the comment form includes the {% csrf_token %} tag, which requires information from the request object, and in order to do so rather than the default context, you need to pass through a RequestContext object instead, but don’t worry too much about the details.

If you now ensure the development server is running and visit a blog post, you should now see that you can post comments. If you want to enhance this very basic comment form, take a look at the excellent documentation on the Django website. Alternatively, there are a number of third-party comment services, such as Disqus and IntenseDebate that can handle comments for you and just require you to paste a snippet of code into whatever template you want to enable comments on, and these may be more convenient.

Finally for this lesson, as promised, we’ll implement our RSS feed. Again, there’s an application bundled with Django that will do this - the syndication framework. Open settings.py and paste the following line in at the bottom of your INSTALLED_APPS:

     'django.contrib.syndication',

Save the file and run python manage.py syncdb to add the appropriate tables to your database. Then, we need to add a URLconf for the RSS feed. We’ll allow a consistent naming scheme for RSS feeds, so this will be /feeds/posts, and if you wanted to you could add /feeds/comments, for instance. Add this to you urls.py, before the url for flat pages:

# RSS feeds
url(r'^feeds/posts/$', PostsFeed()),

We’ll also need to tell urls.py where to find PostsFeed(). In this case, we’re going to put it in the view, so add this import line near the top:

from blogengine.views import PostsFeed

Now open blogengine/views.py and add the following line to the import statements at the top:

from django.contrib.syndication.views import Feed

Then add the following class declaration to the bottom:

class PostsFeed(Feed):
title = "My Django Blog posts"
link = "feeds/posts/"
description = "Posts from My Django Blog"
def items(self):
return Post.objects.order_by('-pub_date')[:5]
def item_title(self, item):
return item.title
def item_description(self, item):
return item.text

This is pretty simple. We import the Feed class from thew views provided by the syndication framework, then we base PostsFeed on Feed. We set the title, the link for the feed, and a description for the feed. Then we get the last 5 Post objects in reverse chronological order, and we define each item’s title as the post title. and each item’s description as the text of the post. From here’ it’s pretty easy to see how you could create feeds based on comments, or pretty much any other object that might exist in the database.

And with that done, our blogging engine is pretty-much feature-complete. We have blog posts with comments, categories, an RSS feed, and flat pages, but the look and feel of the site definitely needs some attention. Next time, we’ll make our blogging engine look a little nicer. Once again, the code is available on GitHub in case you find that more convenient.

24th March 2012 6:23 pm

Yet Another Tutorial for Building a Blog Using Python and Django - Part 3

Welcome back! In this installment, we’ll make some changes to our URL structure for blog posts, we’ll add support for multiple authors and static pages, and we’ll add some more templates.

First of all, our URL structure. The existing structure works fine, but it would be better if we included a representation of the date of publication. If you’re familiar with WordPress, you’ll know it offers several different URL forms, one of which is the post name alone as we’re using here, and another of which is the year, month and name. We’ll use the latter of these URL schemes with our blogging engine.

This seems like a good opportunity to introduce the interactive Python shell that comes with Django. Make sure you have a few dummy posts set up, then in the project directory (DjangoBlog/, not the top-level one but the one inside that), enter the following command:

python manage.py shell

This will start up an interactive Python shell which you can use to interact with your Post objects. Now, the first step is to import your Post model:

>>> from blogengine.models import Post

We now have access to our Post objects – let’s take a look at them:

>>> Post.objects.all()
[<Post: My first blog post>, <Post: My second blog post>, <Post: My third post>, <Post: My fourth post>, <Post: My fifth post>, <Post: My sixth post>]

You may have completely different post objects, or a different number of them, but that’s fine. Remember we set __unicode__(self) to return self.title? Here we see that each blog post is represented by its title. Now let’s get one of our Post objects:

>>> p = Post.objects.get(pk=1)
>>> p
<Post: My first blog post>

In the first line above, we get the Post object with the primary key of 1, and store a reference to it as p. We then demonstrate that it is, indeed, one of our blog posts by outputting its title.

If you’re not familiar with relational database theory, a primary key is a value in a database table that refers uniquely to one entry in the table, so that if you refer to an entry by its primary key, you can be sure you’re getting the correct value. By default, Django models generate a field called id in addition to the ones you define, which is set as the primary key, and this is set to auto-increment, so for instance, every time you add an additional blog post, it gets the next number as its id. Here, we just want to get access to a single blog post object, so we just enter 1 as the primary key in order to get the earliest blog post.

Next, we get the publication date:

>>> p.pub_date
datetime.datetime(2012, 3, 19, 12, 11, 10)

This returns a datetime.datetime object. If you look at the documentation for Python’s datetime module, you’ll notice that it has attributes called day, month and year. Here’s how we can use these to get the information we want:

>>> p.pub_date.month
3
>>> p.pub_date.day
19
>>> p.pub_date.month
3
>>> p.pub_date.year
2012

It’s that simple – we just refer to the attribute we want to retrieve. So, it should now be pretty easy to understand how we can get the date for each blog post.

Exit your Python shell with Ctrl-D and head back into the blogengine/ folder. Then open models.py in your text editor and add the following method to the bottom of your Post class:

def get_absolute_url(self):
return "/%s/%s/%s/" % (self.pub_date.year, self.pub_date.month, self.slug)

Now, you haven’t seen get_absolute_url before. Every time you create a model in Django, you should really create a get_absolute_url method for it. In essence, it defines a single, canonical URL for that object, whether it’s a blog post, a user, or what have you. By creating one method that defines the structure for the URL for this type of object and referring to it elsewhere, we only need to change it in one place if we want to make any changes to how we determine the URL for that type of object.

What we do here is we define the URL as being /year/month/slug/. If you want, you can quite easily make it include the day as well like this:

def get_absolute_url(self):
return "/%s/%s/%s/%s/" % (self.pub_date.year, self.pub_date.month, self.pub_date.day, self.slug)

With our model updated, let’s change our URLconf accordingly. Return to the inner DjangoBlog/ directory and open up urls.py, then amend the lines for the blog posts as follows:

# Blog posts
url(r'^\d{4}/\d{1,2}/(?P<postSlug>[-a-zA-Z0-9]+)/?$', 'blogengine.views.getPost'),

What we’ve changed here is that we’ve told urls.py to expect blog posts that look like 4 digits, then a forward slash, then one or two digits, then another forward slash, then a slug that can include hyphens, upper or lower case letters, and numbers.

With that done, we just need to update our template. Edit templates/posts.html to look like this:

<html>
<head>
<title>My Django Blog</title>
</head>
<body>
{% for post in posts %}
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
<h3>{{ post.pub_date }}</h3>
{{ post.text }}
{% endfor %}
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
</body>
</html>

Literally all we do is replace post.slug with post.get_absolute_url and remove the leading forward slash. If you then run python manage.py syncdb, restart the development server and go clicking around your posts, you should be able to see that our new URL system is now up and running.

With that done, the next step is to add support for multiple authors. Now, you might think that we’re going to have to create a new model for users, but that’s not so – Django ships with a number of useful models already, and we’re going to use one of them here.

Now, first of all, we need to amend our Post model to include the author’s details. Edit your blogengine/models.py to look like this:

from django.db import models
from django.contrib.auth.models import User
# Create your models here.
class Post(models.Model):
title = models.CharField(max_length=200)
pub_date = models.DateTimeField()
text = models.TextField()
slug = models.SlugField(max_length=40, unique=True)
author = models.ForeignKey(User)
def __unicode__(self):
return self.title
def get_absolute_url(self):
return "%s/%s/%s/" % (self.pub_date.year, self.pub_date.month, self.slug)

There are two significant changes here. First, we import User from django.contrib.auth.models. User is a model provided by the auth model, and we’re going to use it here to represent the author of a given post. Then in the class definition of Post, we add a new field called author.

Note here that author is a foreign key field, and is passed a User object. Again for those unfamiliar with relational databases, a foreign key is a field in a database table that is also a primary key in another database table. Here we’re declaring that the author is one of the entries in the User table.

As well as this, we need to make some changes to the admin interface. By default, when we make a field in a model a foreign key, the admin interface will show a dropdown list of all of the instances of that object (so here, it would be a list of all the users on the system). But we don’t want that. We want the author to automatically be set as the current user, and for there to be no way to override this.

Open up admin.py and change it to look like this:

import models
from django.contrib import admin
from django.contrib.auth.models import User
class PostAdmin(admin.ModelAdmin):
prepopulated_fields = {"slug": ("title",)}
exclude = ('author',)
def save_model(self, request, obj, form, change):
obj.author = request.user
obj.save()
admin.site.register(models.Post, PostAdmin)

The changes made here are simple. We import the User model, and in the PostAdmin class definition we exclude the author field – this means that we don’t show this field at all.

Note the addition of the save_model method. In Django it’s easy to create a new object using your models:

>>> from blogengine.models import Post
>>> p = Post()
>>> p
<Post: >
>>> p.title="My new blog post"
>>> p
<Post: My new blog post>

However, the new object won’t actually be stored in the database properly until you call the save() method. Here, you would need to enter p.save() (Note this won’t actually work unless you enter all the fields manually). What we’re doing in admin.py is overriding the default save() method to set the author to the name of the user who wrote the post.

Now run python manage.py syncdb again. Note that as you’ve changed the Post model, your existing posts will be lacking the required author field, and so you may need to add these again manually – this will be a numeric ID mapping to a user id. If you only have one user set up, you should just be able to set this to 1 by using an UPDATE SQL query.

If you now make sure the development server is running and log into the administrative interface, the first page you see should have a section marked “Auth”, with two items underneath named Groups and Users.

Now, cast your mind back to when you activated the admin interface and synced the database. If you recall, at this time you were asked to create a superuser account in order to log into the admin interface. This was actually provided by the django.contrib.auth application, one of the applications that are shipped with Django and are active by default. This contains the User and Group models.

If you’re familiar with Linux or Unix, the Auth application will feel very familiar. The account you created at the start was a superuser account, much like the root account on a Unix system, with unlimited privileges. Other users can be created, and given permissions on an individual basis. You can also create groups and add users to those groups, and then set the privileges for those groups en masse. For instance, in a large collaborative blog with many authors, you may have one group for people who contribute articles who can create new posts, editors who can edit existing posts and so on. Similarly, if you had a working comments system, you could easily set up a moderators group who can delete comments, and add people to that group.

Let’s create another user account so we have more than one. From the main admin page, click on the link for Add next to Users. You’ll be taken to a screen that prompts you for a username and password for the new user. Fill these in (there are two password fields for confirmation purposes) as you wish – here I’m setting the new user as bob. On the next screen you can add some additional details for the new user account, such as first name, last name and email address – do this so you have some information to work with.

Lower down you’ll see a dialogue for entering the permissions. You can make the new user a superuser so that they have permission to do anything, you can say whether or not they are staff (they need to be staff to use the admin interface, so check that), and whether they are active (making it easy to deactivate a user account without the need to delete it). Below you’ll see another dialogue showing the available permissions and allowing you to allocate them to that user. Further down, you’ll see a dialogue for changing the start date and last login date for the user, and finally a dialogue for adding new groups and adding the user to existing groups.

Save the user details once you’re done, then go into your superuser account and add a first and last name so we have some data to work with for that as well. Note that just as with a root account on a Unix box, it’s not a great idea to use a superuser account for everyday work (you should create an account that has the minimum privileges you need and use that), but we’ll stick with it for now just for learning purposes – don’t forget if you should roll out a public facing Django-powered site in future, though!

With that done, we now have some data to work with to identify the author of a given post. Let’s fire up the interactive shell again with python manage.py shell:

>>> from blogengine.models import Post
>>> Post.objects.all()
[<Post: My first post>]
>>> p = Post.objects.get()
>>> p
<Post: My first post>
>>> p.author
<User: root>
>>> p.author.first_name
u'Matthew'
>>> p.author.last_name
u'Daly

Here, we can see that it’s easy to get the author’s details from the post. We define p as a reference to the single Post object,then we get the author, which in this case is called root. As I’ve defined a first and last name, we can get those too with p.author.first_name and p.author.last_name, which are strings containing the first and last name respectively. Note the ‘u’ before the string – this just indicates that the string is Unicode.

So from here, it’s pretty easy to display the author’s name in each post. Go into templates/posts.html and add the following line where you want your author details to appear:

        <h3>By {{ post.author.first_name }} {{ post.author.last_name }}</h3>

Now, as long as you’ve added a first name and last name to that author’s details, if you visit http://127.0.0.1:8000, you should see the appropriate details.

Our next step is to add the facility to create flat pages, somewhat like the Pages functionality in WordPress. Again, Django comes with an application that will handle this, called flatpages, but it’s not enabled by default. Go into DjangoBlog/settings.py and at the bottom of INSTALLED_APPS, add the following:

    'django.contrib.flatpages',

Then run python manage.py syncdb again to add the appropriate tables to your database. Now, we need to add a flat page. Go back to the main page of the admin interface, and you should see that you now have the facility to add flat pages. Click on the Add link for flat pages, and give your page a URL, a title, and some text (here I’m giving it a URL of /about/ and a title of About), add it to a site at the bottom (this will say example.com, but don’t worry about that, it’s to do with the Sites application, which we’re not looking at right now) then save it. You should now have a FlatPage object available.

Let’s take a look at the tables created for flatpages using the sqlall command:

python manage.py sqlall flatpages
BEGIN;
CREATE TABLE "django_flatpage_sites" (
"id" integer NOT NULL PRIMARY KEY,
"flatpage_id" integer NOT NULL,
"site_id" integer NOT NULL REFERENCES "django_site" ("id"),
UNIQUE ("flatpage_id", "site_id")
)
;
CREATE TABLE "django_flatpage" (
"id" integer NOT NULL PRIMARY KEY,
"url" varchar(100) NOT NULL,
"title" varchar(200) NOT NULL,
"content" text NOT NULL,
"enable_comments" bool NOT NULL,
"template_name" varchar(70) NOT NULL,
"registration_required" bool NOT NULL
)
;
CREATE INDEX "django_flatpage_a4b49ab" ON "django_flatpage" ("url");
COMMIT;

So we can see that django_flatpage, which contains the details about the actual flat pages, has the fields id, url, title, content, enable_comments, template_name, and registration_required. Some of these options are under the advanced options in the flat page interface, so you may have missed them. Now fire up python manage.py shell again:

>>> from django.contrib.flatpages.models import FlatPage
>>> f = FlatPage.objects.get()
>>> f
<FlatPage: /about/ -- About>

Here we have one FlatPage object only (note that get() should only be used if you will only get one result back), which is represented by a string that includes the URL and title.

>>> f.content
u'This is my about page.'

We can easily access any of the fields in the flat page. Now, we need to define some URLs for our flat pages. Exit the Python shell and open urls.py, then insert the following rule underneath the one for blog posts:

# Flat pages
url(r'', include('django.contrib.flatpages.urls')),

Note that this must be the last rule in your urls.py, because it will match anything. Now, you can try and load /about/, or whatever page you’ve created, but you’ll get an error stating that the template does not exist, so we need to create that. Go into your template directory, and create a directory inside that called flatpages. Then create a new file in there called default.html, and add the following code to it:

<html>
<head>
<title>My Django Blog</title>
</head>
<body>
<h1>{{ flatpage.title }}</h1>
{{ flatpage.content }}
</body>
</html>

Now, make sure you have the development server running and try to load http://127.0.0.1:8000/about/, or whatever your flat page URL is, and you should see your flat page’s title and content.

One final task for this lesson – we’re going to refactor our templates a little so that as little code as possible is duplicated and if we want to change anything we need to only do so in one place. Go to your template directory and edit posts.html to look like this:

{% include 'header.html' %}
{% for post in posts %}
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
<h3>{{ post.pub_date }}</h3>
{{ post.text }}
<h3>By {{ post.author.first_name }} {{ post.author.last_name }}</h3>
{% endfor %}
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
{% include 'footer.html' %}

Here we’re taking the header and footer of the page out and replacing them with code that includes another file there instead. Next, we need to create those files in the same directory. Here’s header.html:

<html>
<head>
<title>My Django Blog</title>
</head>
<body>

And here’s footer.html:

</body>
</html>

None of this is terribly complex – we’re just moving the code into another file so that other templates can use the same files. Now save a copy of posts.html as single.html – we’re going to create a template for a single blog post. Edit the original posts.html to look like this:

{% include 'header.html' %}
{% for post in posts %}
<h1><a href="{{ post.get_absolute_url }}">{{ post.title }}</a></h1>
{{ post.text }}
{% endfor %}
<br />
{% if page.has_previous %}
<a href="/{{ page.previous_page_number }}/">Previous Page</a>
{% endif %}
{% if page.has_next %}
<a href="/{{ page.next_page_number }}/">Next Page</a>
{% endif %}
{% include 'footer.html' %}

We’re just removing the date and author details from the template that shows multiple posts. Our existing single.html file can remain as it is for now, since that still has all the additional information we want to include in an individual post.

While we’re here, let’s update our flat pages to use the same header and footer. Go into the flatpages directory and change default.html to look like this:

{% include 'header.html' %}
<h1>{{ flatpage.title }}</h1>
{{ flatpage.content }}
{% include 'footer.html' %}

Note that the path to the template files is not relative to flatpages/default.html, but relative to the root of the template directory.

The last thing to do is to amend the view for our blog to use the correct templates. Go into blogengine/views.py and change the getPost (NOT getPosts) function to pass the single.html template to render_to_response, instead of the posts.html template:

# Display specified post
return render_to_response('single.html', { 'posts':post})

You should now notice that the single posts and multiple posts are using different templates.

Hope you’ve enjoyed this lesson, and I’ll do another one as soon as I can. The code is available on GitHub if you prefer to get it that way.

Recent Posts

Mutation Testing With Infection

Switching from Vim to Neovim

Better Strings in PHP

Forcing SSL in Codeigniter

Logging to the ELK Stack With Laravel

About me

I'm a web and mobile app developer based in Norfolk. My skillset includes Python, PHP and Javascript, and I have extensive experience working with CodeIgniter, Laravel, Django, Phonegap and Angular.js.