Django TastyPie's Extended ModelResource

The ExtendedModelResource is an extension for TastyPie's ModelResource that adds some interesting features:

Supports easily using resources as nested of another resource, with proper authorization checks for each case.
Supports using a custom identifier attribute for resources in uris (not only the object's pk!)

Requirements

Required

django-tastypie 0.9.11 and its requirements.

Optional

Django 1.4 for the sample project.

Installation

Clone repository and do:

python setup.py install

Or just do

pip install django-tastypie-extendedmodelresource

to get the latest version from pypi.

Nested resources

Here we explain what we mean by nested resources and what a simple use case would be.

Rationale

Imagine you have a simple application which has users, each of which can write any number of entries. Every entry is associated to a user. For example

from django.contrib.auth.models import User
from django.db import models


class Entry(models.Model):
    user = models.ForeignKey(User, related_name='entries')
    # ... more fields

The 'standard' TastyPie models for this would be

from django.contrib.auth.models import User
from tastypie.resources import ModelResource

from myapp.models import Entry


class UserResource(ModelResource):
    class Meta:
        queryset = User.objects.all()

class EntryResource(ModelResource):
    class Meta:
        queryset = Entry.objects.all()

This gives you full CRUD ability over users and entries, with uris such as /api/user/ and /api/entry/.

Now imagine you want to be able to easily list all the entries authored by a given user, with a uri such as /api/user/<pk>/entries. Additionally, you would like to be able to POST to this uri and create an entry automatically associated to this user. This is why nested resources are for.

If a resource such as the EntryResource is to be accessed as /api/user/<pk>/<something> where <something> is custom-defined (for example entries), then we say the EntryResource is being used as nested of the UserResource. We also say that UserResource is the parent of EntryResource.

The standard TastyPie's ModelResource would force you to write a function overriding the urls of the UserResource and adding a method to handle the entry resource (see Nested Resources). Using ExtendedModelResource it is as easy as

from django.contrib.auth.models import User
from tastypie import fields

from extendedmodelresource import ExtendedModelResource
from myapp.models import Entry


class UserResource(ExtendedModelResource):
    class Meta:
        queryset = User.objects.all()

    class Nested:
        entries = fields.ToManyField('api.resources.EntryResource', 'entries')


class EntryResource(ExtendedModelResource):
    user = fields.ForeignKey(UserResource, 'user')

    class Meta:
        queryset = Entry.objects.all()

And that's it!

How authorization is handled

If a resource does not have a nested resource, the authorization is handled the same way as in the standard TastyPie. You define an Authorization class and associate it to the resource. This class may implement the is_authorized and apply_limits methods.

For an ExtendedModelResource with nesteds, all the authorization when using the nested as such is handled from the authorization class of the parent resource. For each resource used as nested, the Authorization class of the parent can implement two methods:

is_authorized_nested_<attribute>
apply_limits_nested_<attribute>

where <attribute> is the name of the attribute parameter in the ApiField that declares the resource as nested. These functions work identically to the original ones, except that they also receive a parent_object parameter which will contain the parent object.

For our users and entries example, an Authorization can be something like:

from tastypie.authorization import Authorization


class UserResourceAuthorization(Authorization):
    """
    Our Authorization class for UserResource and its nested.
    """

    def is_authorized(self, request, object=None):
        # Only 'newton' is authorized to view the users
        if 'newton' in request.user.username:
          return True

        return False

    def apply_limits(self, request, object_list):
        return object_list.all()

    def is_authorized_nested_entries(self, request,
                                     parent_object, object=None):
        # Is request.user authorized to access the EntryResource as
        # nested?
        return True

    def apply_limits_nested_entries(self, request, parent_object,
                                   object_list):
        # Advanced filtering.
        # Note that object_list already only contains the objects that
        # are associated to parent_object.
        return object_list.all()

Caveats

ExtendedModelResource only supports one level nesting.
Resources used as nested can also be registered in an Api instance, but need not to. That is, there can be resources used only as nested and not exposed otherwise in the urls.

Changing object's identifier attribute in urls

With TastyPie's ModelResource you can override a method to change the identifier attribute used for objects in the URLs (see Using Non-PK Data For Your URLs)

class UserResource(ModelResource):
    class Meta:
        queryset = User.objects.all()

    def override_urls(self):
        return [
            url(r"^(?P<resource_name>%s)/(?P<username>[\w\d_.-]+)/$" % self._meta.resource_name, self.wrap_view('dispatch_detail'), name="api_dispatch_detail"),
        ]

This adds a new URL using username and ignores the old URL using pk

^api/ ^(?P<resource_name>user)/(?P<username>[\w\d_.-]+)/$ [name='api_dispatch_detail']
^api/ ^(?P<resource_name>user)/$ [name='api_dispatch_list']
^api/ ^(?P<resource_name>user)/schema/$ [name='api_get_schema']
^api/ ^(?P<resource_name>user)/set/(?P<pk_list>\w[\w/;-]*)/$ [name='api_get_multiple']
^api/ ^(?P<resource_name>user)/(?P<pk>\w[\w/-]*)/$ [name='api_dispatch_detail']

But the old URL is still there, and this can be a bit confusing when you have an error with the URLs.

Using ExtendedModelResource it is as easy as adding a new entry in the Meta class

class UserResource(ExtendedModelResource):
    class Meta:
        queryset = User.objects.all()
        url_id_attribute = 'username'

And you will get this list of urls

^api/ ^(?P<resource_name>user)/$ [name='api_dispatch_list']
^api/ ^(?P<resource_name>user)/schema/$ [name='api_get_schema']
^api/ ^(?P<resource_name>user)/set/(?P<username_list>(\w[\w-]*;?)*)/$ [name='api_get_multiple']
^api/ ^(?P<resource_name>user)/(?P<username>\w[\w-]*)/$ [name='api_dispatch_detail']

If you need to change the regular expression used for your identifier attribute in the urls, you can override the method get_url_id_attribute_regex and return it, like the following example

def get_url_id_attribute_regex(self):
    return r'[aA-zZ][\w-]*'

More information

Date:	04-19-2012
Version:	0.1
Authors:	Alan Descoins - Tryolabs <alan@tryolabs.com> Martín Santos - Tryolabs <santos@tryolabs.com>
Website:	https://github.com/tryolabs/django-tastypie-extendedmodelresource

tadeck/django-tastypie-extendedmodelresource