Synopsis

This module is an add-on for Django REST Framework that serves a django model respecting the Linked Data Platform convention.

It aims at enabling people with little development skills to serve their own data, to be used with a LDP application.

Building a Startin' Blox application? Read this: https://git.happy-dev.fr/startinblox/devops/doc

Requirements

• Django (known to work with django 1.11)
• Django Rest Framework
• pyld
• django-guardian
• djangorestframework-guardian

Installation

1. Install this module and all its dependencies

$ pip install djangoldp

2. Create a django project

$ django-admin startproject myldpserver

3. Add DjangoLDP to INSTALLED_APPS

INSTALLED_APPS = [
    ...
    # make sure all of your own apps are installed BEFORE DjangoLDP
    'djangoldp.apps.DjangoldpConfig',
]

IMPORTANT: DjangoLDP will register any models which haven't been registered, with the admin. As such it is important to add your own apps above DjangoLDP, so that you can use custom Admin classes if you wish

4. Create your django model inside a file myldpserver/myldpserver/models.py Note that container_path will be use to resolve instance iri and container iri In the future it could also be used to auto configure django router (e.g. urls.py)

from djangoldp.models import Model

class Todo(Model):
    name = models.CharField(max_length=255)
    deadline = models.DateTimeField()

4.1. Configure container path (optional) By default it will be "todos/" with an S for model called Todo

<Model>._meta.container_path = "/my-path/"

4.2. Configure field visibility (optional) Note that at this stage you can limit access to certain fields of models using

<Model>._meta.serializer_fields (<>list of field names to show>)

For example, if you have a model with a related field with type django.contrib.auth.models.User you don't want to show personal details or password hashes.

E.g.

from django.contrib.auth.models import User

User._meta.serializer_fields  = ('username','first_name','last_name')

Note that this will be overridden if you explicitly set the fields= parameter as an argument to LDPViewSet.urls(), and filtered if you set the excludes= parameter.

5. Add a url in your urls.py:

from django.conf.urls import url
from django.contrib import admin
from djangoldp.views import LDPViewSet
from .models import Todo

urlpatterns = [
    url(r'^', include('djangoldp.urls')),
    url(r'^admin/', admin.site.urls), # Optional
]

This creates 2 routes for each Model, one for the list, and one with an ID listing the detail of an object.

You could also only use this line in settings.py instead:

ROOT_URLCONF = 'djangoldp.urls'

6. In the settings.py file, add your application name at the beginning of the application list, and add the following lines

STATIC_ROOT = os.path.join(os.path.dirname(BASE_DIR), 'static')
LDP_RDF_CONTEXT = 'https://cdn.happy-dev.fr/owl/hdcontext.jsonld'
DJANGOLDP_PACKAGES = []
SITE_URL = 'http://localhost:8000'
BASE_URL = SITE_URL

• LDP_RDF_CONTEXT tells DjangoLDP where our RDF ontology is defined, which will be returned as part of our views in the 'context' field. This is a web URL and you can visit the value to view the full ontology online
• DJANGOLDP_PACKAGES defines which other DjangoLDP packages we're using in this installation
• SITE_URL is the URL serving the site, e.g. https://example.com/
• BASE_URL may be different from SITE_URL, e.g. https://example.com/app/

7. You can also register your model for the django administration site

from django.contrib import admin
from .models import Todo

admin.site.register(Todo)

8. You then need to have your WSGI server pointing on myldpserver/myldpserver/wsgi.py

9. You will probably need to create a super user

$ ./manage.py createsuperuser

10. If you have no CSS on the admin screens :

$ ./manage.py collectstatic

Execution

To start the server, cd to the root of your Django project and run :

$ python3 manage.py runserver

Custom Parameters to LDPViewSet

lookup_field

Can be used to use a slug in the url instead of the primary key.

LDPViewSet.urls(model=User, lookup_field='username')

nested_fields

list of ForeignKey, ManyToManyField, OneToOneField and their reverse relations. When a field is listed in this parameter, a container will be created inside each single element of the container.

In the following example, besides the urls /members/ and /members/<pk>/, two other will be added to serve a container of the skills of the member: /members/<pk>/skills/ and /members/<pk>/skills/<pk>/

<Model>._meta.nested_fields=["skills"]

Custom Meta options on models

rdf_type

auto_author

This property allows to associate a model with the logged in user.

class MyModel(models.Model):
    author_user = models.ForeignKey(settings.AUTH_USER_MODEL)
    class Meta:
        auto_author = 'author_user'

Now when an instance of MyModel is saved, its author_user property will be set to the current user.

permissions_classes

This allows you to add permissions for anonymous, logged in user, author ... in the url: By default LDPPermissions is used. Specific permissin classes can be developed to fit special needs.

anonymous_perms, user_perms, owner_perms

Those allow you to set permissions from your model's meta.

You can give the following permission to them:

• view
• add
• change
• control
• delete
• inherit

With inherit, Users can herit from Anons. Also Owners can herit from Users.

Eg. with this model Anons can view, Auths can add & Owners can edit & delete.

Note that owner_perms need a owner_field meta that point the field with owner user.

from djangoldp.models import Model

class Todo(Model):
    name = models.CharField(max_length=255)
    deadline = models.DateTimeField()
    user = models.ForeignKey(settings.AUTH_USER_MODEL)

    class Meta:
        anonymous_perms = ['view']
        authenticated_perms = ['inherit', 'add']
        owner_perms = ['inherit', 'change', 'control', 'delete']
        owner_field = 'user'

Important note: If you need to give permissions to owner's object, don't forget to add auto_author in model's meta

view_set

In case of custom viewset, you can use

from djangoldp.models import Model

class Todo(Model):
    name = models.CharField(max_length=255)
    deadline = models.DateTimeField()
    
    class Meta:
        view_set =  TodoViewSet

container_path

See 3.1. Configure container path (optional)

serializer_fields

from djangoldp.models import Model

class Todo(Model):
    name = models.CharField(max_length=255)
    deadline = models.DateTimeField()

    class Meta:
        serializer_fields =  ['name']

Only name will be serialized

Custom urls

To add customs urls who can not be add through the Model class, it's possible de create a file named djangoldp_urls.py. It will be executed like an urls.py file

Pagination

To enable pagination feature just add this configuration to the server settings.py :

REST_FRAMEWORK = {
    'DEFAULT_PAGINATION_CLASS': 'djangoldp.pagination.LDPPagination',
    'PAGE_SIZE': 20
}

Sources

To enable sources auto creation for all models, change djangoldp by djangoldp.apps.DjangoldpConfig, on INSTALLED_APPS

INSTALLED_APPS = [
    'djangoldp.apps.DjangoldpConfig',
]

301 on domain mismatch

To enable 301 redirection on domain mismatch, add djangoldp.middleware.AllowOnlySiteUrl on MIDDLEWARE

This ensure that your clients will use SITE_URL and avoid mismatch betwen url & the id of a resource/container

MIDDLEWARE = [
    'djangoldp.middleware.AllowOnlySiteUrl',
]

Notice tht it'll redirect only HTTP 200 Code.

License

Licence MIT