Django 1.2 released
djangoproject.com
djangoproject.com
>"One of Django's core design philosophies is that template languages shouldn't try to be programming languages. To that end, we've kept the template language deliberately simplisitic so that you'd be more or less forced to push advanced logic up into the view."
Very view people seem to understand this at first unfortunately and try to do crazy things like swap out the template language for something else or add on a bunch of hacks. Why create additional custom template logic and the parsing instructions for converting it to python when you can just write the functionality in probably one line of standard python in your view fuction and have it run faster.
Generic summary: templates should only be able to do substitution, iteration, and existence checks on variables.
There is a reason Django is introducing range checking and simple logic into their template statements. How often do you specify something like:
"If the amount owed is more than $100, make it red in the table"
That's not a question of separation of view/logic in my mind. It's a question of formatting. Forcing the view to resolve it down to a simple boolean statement results in a lot of cruft in the view layer that really doesn't belong there. It is just as evil to move presentation logic into a view as it is the other way around.
Well, my usual advice on this goes back to the first time I encountered someone pushing a similar situation. In that case he was showing government safety ratings for cars, and if the rating was above a certain level wanted to show a special graphic because that got it some special certification.
Rather than try to force that logic into a template, I suggested giving the relevant model a "meets_certification_standard()" method, since that's the sort of thing you'd probably want to reuse for more than just presentation. And in your case I'd bet a similar approach would be the best solution.
And for some reason, i don't personally enjoy polluting my views with statements that do nothing but populate context variables.
That's pretty much all I like to put in views. The rest goes in models/managers, or forms, or elsewhere.
As a very simplistic (and somewhat contrived) example:
% for label in ('Home','Features','Pricing','Contact'):
<li>{{ label }}</li>
% endfor
In my mind, the view should be responsible for dealing with application logic and business logic. E.g. stuff like pulling things out of the database, dealing with GET/POST request data, validating forms, verifying user authentication and permissions, and whatever application specific logic is necessary.
The views should pass their data to the template, but not assume anything about how the template is being rendered, and not be doing things for the template. E.g. if you're doing something that renders a HTML snippet to pass into the template, you've done something wrong.
Once you start going down that road you make it much more difficult to render alternate versions of your templates (for mobile users for example).
Another case where the crippled templating system ends up pushing concerns into the wrong layer is rendering hierarchical data: e.g. a nested comments tree. Deciding how to render that data should be entirely within the scope of the template. But because of the lack of simple recursion support, the 'recommended practice' is to unravel the tree in your view code, and pass the unraveled version into the template. Or write your own template tag, but that is even more complicated.
It's also a bit silly that Django calls controllers 'views' and calls views 'templates', but perhaps it explains why they think it's okay to do view specific rendering at the controller level.
from django.core.urlresolvers import reverse
from django.template import Library
register = Library()
@register.simple_tag
def menu_item(req, viewname, label):
url = reverse(viewname)
cls = ''
if url == req.path:
cls += 'active'
return '<li class="%s"><a href="%s">%s</a></li>' % (cls, url, label)
{% menu_item request 'accounts.views.profile' 'Your Account' %}
A simple filter:
@register.filter
def subtract(x, y):
"""Subtracts the arg from the value"""
return int(x) - int(y)
<li style="z-index: {{ 100|subtract:forloop.counter }}">
Jinja2's macros are a much more elegant solution, IMO.
Another PITA, where Django templates just fall down, is forms. Suppose you have a form:
class MyForm(forms.Form):
name = forms.CharField()
{{ form.name }}
name = forms.CharField(widget=forms.TextInput(attrs={'class' : 'foo'}))
form.fields['name'].widget.attrs = {'class' : 'foo'}
Contrast the following in Jinja2 (using WTForms, but you get the idea):
{{ form.name(class_="foo") }} {% field form.name class="myclass" %} {% form.name|attrs:"class='foo', maxlength=20" %}
Adding a class: Django gives every element of the form id values for easy styling in CSS. Just do {{form.as_p}} and see what it outputs.
size and max length: I'm fine with these in python as they correspond to the max-length that would be validated into a data member. If you mean pixel size on screen, this belongs neither in HTML or your template but in CSS, since browsers render forms completely differently regardless of their HTML attributes, you have to style their width\height in CSS to get anything consistent.
as_p and co. should include some class describing the field type in the outer <p> tag so that a developer can style the label and error messages in a way specific to the field type.
<li>{{home}}</li>
<li>{{home.features}}</li>
<li>{{home.pricing}}</li>
<li>{{home.contact}}</li>
{%for label in home.list%}
<li>{{label}}</li>
{%endfor%}
Edit: also, you can recurse all day long in django with clever use of the {%include%} tag. The {%include%} tag is seriously worth looking into in any complicated situation. Writing your HTML in seperate chunks also make rolling out an AJAX version of the page really easy, because you can just render the included subcomponent in an ajax request instead of the page that includes it, using the same view function.
But who said anything about a Home model? What if I was just adding a list of links to the footer of my page? E.g. things that have nothing to do with the application or data but are necessary for presentation on a webpage.
I believe that the preferred way to do this in Django is by either creating a custom template tag, or by using template inheritance.
Template inheritance: create a base.html template with a {% block footer %} that can inherit and/or over ride it from any other template that needs.
Template Tags:
Create a simple tag that renders the comments thread, what's related links, etc... in a separate tag. This is the "preferred" way if you need to query the database for something that's related to multiple different views. For an example of that, see the django-pagination app.
In my experience not doing this separation encourages people solving controller-level problems on the view level, just because they can. Of course, it's just a "quick fix, I'll fix that properly later" everytime that happens. This philosophy is what drew me to Django in the first place, I really dislike HTML fragments in code, and having done enough rewriting of code when it's time to redesign the web site makes this a big feature for me.
Of course, being Django, it's loosely coupled and you can easily switch out the template language to something else.
I find it seriously irritating when silly limitations like this in a framework corner you into bad data design.
Frameworks by their very definition are not meant to cover 100% of use cases. They cover the 80% of issues that can be solved without composite keys, or those where the overhead in not having the correct design is negligible.
Perhaps in these cases you shouldn't be forcing the framework into a position it can't fit.
"Object-level permissions"
get_all_permissions(obj=None)
New in Django 1.2
If obj is passed in, only returns the permissions for this specific object.
It might be related to this? http://docs.djangoproject.com/en/dev/releases/1.2/#customiza...
just kidding
/me ducks