Django ease of building a RESTful interface

Question

I'm looking for an excuse to learn Django for a new project that has come up. Typically I like to build RESTful server-side interfaces where a URL maps to resources that spits out data in some platform independent context, such as XML or JSON. This is rather straightforward to do without the use of frameworks, but some of them such as Ruby on Rails conveniently allow you to easily spit back XML to a client based on the type of URL you pass it, based on your existing model code.

My question is, does something like Django have support for this? I've googled and found some 'RESTful' 3rd party code that can go on top of Django. Not sure if I'm too keen on that.

If not Django, any other Python framework that's already built with this in mind so I do not have to reinvent the wheel as I already have in languages like PHP?

Answer 1

This is probably pretty easy to do.

URL mappings are easy to construct, for example:

urlpatterns = patterns('books.views',
  (r'^books/$', 'index'),
  (r'^books/(\d+)/$', 'get'))

Django supports model serialization, so it's easy to turn models into XML:

from django.core import serializers
from models import Book

data = serializers.serialize("xml", Book.objects.all())

Combine the two with decorators and you can build fast, quick handlers:

from django.http import HttpResponse
from django.shortcuts import get_object_or_404

def xml_view(func):
  def wrapper(*args, **kwargs):
    result = func(*args, **kwargs)
    return HttpResponse(serializers.serialize("xml", result),
        mimetype="text/xml")
  return wrapper

@xml_view
def index(request):
  return Books.objects.all()

@xml_view
def get(request, id):
  return get_object_or_404(Book, pk=id)

Answer 2

(I had to edit out the most obvious links.)

+1 for piston - (link above). I had used apibuilder (Washington Times open source) in the past, but Piston works easier for me. The most difficult thing for me is in figuring out my URL structures for the API, and to help with the regular expressions. I've also used surlex which makes that chore much easier.

Example, using this model for Group (from a timetable system we're working on):

class Group(models.Model):
    """
    Tree-like structure that holds groups that may have other groups as leaves. 
    For example ``st01gp01`` is part of ``stage1``.
    This allows subgroups to work. The name is ``parents``, i.e.::

        >>> stage1group01 = Group.objects.get(unique_name = 'St 1 Gp01')
        >>> stage1group01
        >>> <Group: St 1 Gp01>
        # get the parents...
        >>> stage1group01.parents.all()
        >>> [<Group: Stage 1>]

    ``symmetrical`` on ``subgroup`` is needed to allow the 'parents' attribute to be 'visible'.
    """
    subgroup = models.ManyToManyField("Group", related_name = "parents", symmetrical= False, blank=True)
    unique_name = models.CharField(max_length=255)
    name = models.CharField(max_length=255)
    academic_year = models.CharField(max_length=255)
    dept_id = models.CharField(max_length=255)
    class Meta:
        db_table = u'timetable_group'
    def __unicode__(self):
        return "%s" % self.name

And this urls.py fragment (note that surlex allows regular expression macros to be set up easily):

from surlex.dj import surl
from surlex import register_macro
from piston.resource import Resource
from api.handlers import GroupHandler
group_handler = Resource(GroupHandler)

# add another macro to our 'surl' function
# this picks up our module definitions
register_macro('t', r'[\w\W ,-]+')

urlpatterns = patterns('',
# group handler
# all groups
url(r'^groups/$', group_handler),
surl(r'^group/<id:#>/$', group_handler),
surl(r'^group/<name:t>/$', group_handler),)

Then this handler will look after JSON output (by default) and can also do XML and YAML.

class GroupHandler(BaseHandler):
    """
    Entry point for Group model
    """

    allowed_methods = ('GET', )
    model = Group
    fields = ('id', 'unique_name', 'name', 'dept_id', 'academic_year', 'subgroup')

    def read(self, request, id=None, name=None):
        base = Group.objects
        if id:
            print self.__class__, 'ID'
            try:
                return base.get(id=id)
            except ObjectDoesNotExist:
                return rc.NOT_FOUND
            except MultipleObjectsReturned: # Should never happen, since we're using a primary key.
                return rc.BAD_REQUEST
        else:
            if name:
                print self.__class__, 'Name'
                return base.filter(unique_name = name).all()
            else:
                print self.__class__, 'NO ID'
                return base.all()

As you can see, most of the handler code is in figuring out what parameters are being passed in urlpatterns.

Some example URLs are api/groups/, api/group/3301/ and api/group/st1gp01/ - all of which will output JSON.