The Django {% url %} templatetag raises a NoReverseMatch error when it can't reverse the provided URL. This is useful in development, but in production, this stops the user dead in their tracks with an ugly 500 error, blocking the whole page, and leading them to think our site is broken.
Template developers shouldn't be able to bring down the whole site with a typo. What I want to do is transparently override this behavior so that, in production only, if a reverse match can't be found, it outputs a default url, like "#", and reports the error to our exception tracking system in the background, but still lets the user continue with what they were doing without raising the 500 error.
Is there a way to replace the default {% url %} tag with my own safer version, transparently? I don't want to have to add a {% load my_custom_url_tag %} at the top of every single template on the site, because at some point people will forget, and the behavior of the tag is will otherwise be the same, the only difference is how it handles errors.
You can use the built-in url tag in silent mode, try the lookup, and then use the URL it finds—if it finds something.
From the Django docs:
This {% url ... as var %} syntax will not cause an error if the view is missing. In practice you’ll use this to link to views that are optional:
{% url 'path.to.view' as the_url %}
{% if the_url %}
Link to optional stuff
{% endif %}
Hope that helps.
By implementing your own url tag, you're opening yourself up to lots of forward compatibility issues. My recommendation would be to add custom 500 error handler instead: https://docs.djangoproject.com/en/1.4/topics/http/views/#the-500-server-error-view
I would think you would actually want the view to throw an error if a template developer has made a typo. Trying to mask that behavior seems illogical - isn't that reason enough to have some simple unit tests to make sure your views are at least returning a 200 response code?
Related
According to the docs of url the_url is empty if the reverse of the url fails:
{% url 'some-url-name' as the_url %}
In my case I would like to get an exception, since I want my tests to fail if my code is broken.
How to store the result of reverse to a variable (and get an exception if the reverse failed)?
Depends on what you really want to test...
If you only want to test whether "'some-url-name'" can be reversed (regardless of how it's used in templates), the {% url %} tag is mainly a wrapper around django.core.urlresolvers.reverse so that's easy to unittest.
If you want to test that your urls are correctly reversed in your templates, well, the solution is simple: render the template and parse the html to check if the url is ok ;-)
NB: Django has some doc on the topic and a couple useful tools
When I read django code sometimes, I see in some templates "load url from future". I am not quite sure what this is but I do know it has something to do with URLs. How and when is this load url from future supposed to be used?
It's due to a change to the url tag enacted in 1.3:
Changes to url and ssi
Most template tags will allow you to pass in either constants or variables as arguments – for example:
{% extends "base.html" %}
allows you to specify a base template as a constant, but if you have a context variable templ that contains the value base.html:
{% extends templ %}
is also legal.
However, due to an accident of history, the url and ssi are different. These tags use the second, quoteless syntax, but interpret the argument as a constant. This means it isn’t possible to use a context variable as the target of a url and ssi tag.
Django 1.3 marks the start of the process to correct this historical accident. Django 1.3 adds a new template library – future – that provides alternate implementations of the url and ssi template tags. This future library implement behavior that makes the handling of the first argument consistent with the handling of all other variables. So, an existing template that contains:
{% url sample %}
should be replaced with:
{% load url from future %}
{% url 'sample' %}
The tags implementing the old behavior have been deprecated, and in Django 1.5, the old behavior will be replaced with the new behavior. To ensure compatibility with future versions of Django, existing templates should be modified to use the new future libraries and syntax.
I will put this in a separate answer due to the following salient Exception in connection with templates:
If you get a django.core.urlresolvers.NoReverseMatch Exception thrown from within a django template (Django version >1.4) parser, it may just be the usage of {% load url from future %} within the template.
In this case, simply quote the url that is passed to the url-tag. That is {% url someurl %} should become {% url 'someurl' %}. Thanks to Ignacio VA for pointing me in that direction.
I don't know if this SO question is of the same problem that I am about to describe, but it does share the same symptoms. Unfortunately, it still remains unresolved as I am writing.
So here is my problem. I am trying to add James Bennett's django-registration app to my django project. I have pretty much finished configuring it to my needs - custom templates and urls. Just when I thought everything was good to go. I got NoReverseMatch error from using {% url 'testing' item_id=123 %} (I also tried using the view name, myapp.views.test, instead but no luck) in one of the custom templates required by django-registration. Interestingly, I tried reverse('testing', kwargs={'item_id':123}) in the shell and the url was returned just fine. I thought {% url %} uses reverse() in the back-end but why did I get different outcomes?
urls.py: (the URLconf of my site)
urlpatterns = patterns('myapp.views',
url(r'^test/(?P<item_id>\d+)/$', 'test', name='testing'),
)
activation_email.txt: (the said template. Note it's intentionally in .txt extension as required by django-registration and that shouldn't be the cause of the problem.)
{% comment %}Used to generate the body of the activation email.{% endcomment %}
Welcome to {{ site }}! Please activate your account by clicking on the following link:
{% url 'testing' item_id=123 %}
Note the activation link/code will be expired in {{ expiration_days }} days.
I don't know if it matters but just thought I should mention activation_email.txt is stored in the templates directory of myapp though it is used by django-registration.
Also, I am using django 1.4
I have a feeling that the problem has something to do with the url namespaces, a topic that I have never understood, but it's just a naive guess. (IMO, the django documentation is great in explaining everything about django, except when it comes to url namespaces)
I'm no expert here, but in a Django project I'm working on at the moment I use the name of the url without quotes. I just added quotes around a similar line in one of my templates and it produced the same error as your error.
Try:
{% url testing item_id=123 %}
Is it possible to implement facebook style loading of content while scrolling down? I would like to implement it in an ecommerce site. There are a lot of items in each category and the category page becomes too long. I could implement page numbers but my client wants me to implement that facebook type of loading. Is there anything I can use? Rest of the site has already been built.
I did look into django-endless-pagination but was not able to get it to work. Is there any demo of it so that I can look into it?
We used django endless pagination on www.mymommemories.com without too much problem. Because we were using html5media we did have to add a line to run that function with a one second delay. (setTimeOut("html5media()", 1000). Running it without the delay caused problems in some browsers. If your not using html5media, this should not be a concern however.
Core part of the template code.
{% load endless %}
{% paginate memories %}
{% for memory in memories %}
.
.
.
{% endfor %}
{% show_more %}
In the view we have the following to handle the ajax request.
if request.is_ajax():
template = page_template
return render_to_response(template,context,context_instance=RequestContext(request))
The page_template is not the whole page, just the portion related to the "paging".
I thinks the easiest way to do endless pagination is use jQuery (use $.loads).
You even don't need change the back-end code.
http://www.infinite-scroll.com/infinite-scroll-jquery-plugin/
Perhaps take a look at that?
for some reason, templatetags do not render in templates for django admin.
with this snippet from:
http://docs.djangoproject.com/en/dev/ref/templates/api/?from=olddocs#shortcut-for-simple-tags
{% if is_logged_in %}Thanks for logging in!{% else %}Please log in.{% endif %}
when placed in admin index.html, if a user is logged in, it shows "Please log in"
same with templatetags, can not get any app ones to show, do anything. there is no error/they do not get processed either
That's only an example, the is_logged_in variable is not actually defined in any templates unless you put it in the context.
If you added that line and got Please log in. it does mean that the tag is rendering. If it fails the if and goes to the else it is clearly being run. You need to find something in the template you can actually use for the if case, though. I haven't messed with the admin templates in newforms-admin, but depending if they use RequestContext and on which ContextProcessors you have enabled - you might be able to say {% if not request.user.is_anonymous %} ... or something similar.
I just tried this one:
request.user.is_authenticated
Right in the template and just worked as we wish!