Django/PostgreSQL implementation of the Meteor DDP service.
Project description
Django/PostgreSQL implementation of the Meteor DDP service, allowing Meteor to subscribe to changes on Django models.
Requirements
The core concept is that events are dispatched asynchronously to browsers using WebSockets and server-side using a PostgreSQL extension to the SQL syntax called NOTIFY (and its bretheren, LISTEN and UNLISTEN). You must be using PostgreSQL with psycopg2 in your Django project for django-ddp to work. There is no requirement on any asynchronous framework such as Reddis or crossbar.io as they are simply not needed given the asynchronous support provided by PostgreSQL with psycopg2. As an added bonus, events dispatched using NOTIFY in a transaction are only emitted if the transaction is successfully committed.
Scalability
All database queries to support DDP events are done once by the server instance that has made changes via the Django ORM. Django DDP multiplexes messages for active subscriptions, broadcasting an aggregated change message on channels specific to each Django model that has been published.
Peer servers subscribe to aggregate broadcast events only for channels (Django models) that their connected clients subscribe to. The aggregate events received are de-multiplexed and dispatched to individual client connections. No additional database queries are required for de-multiplexing or dispatch by peer servers.
Limitations
The 0.2.x release series only supports DDP via WebSockets. Future development may resolve this by using SockJS, to support browsers that don’t have WebSockets.
Changes must be made via the Django ORM as django-ddp uses Django signals to receive model save/update signals.
Installation
Install the latest release from pypi (recommended):
pip install django-ddpClone and use development version direct from GitHub (to test pre-release code):
pip install -e git+https://github.com/commoncode/django-ddp@develop#egg=django-ddpExample usage
Add ‘dddp’ to your settings.INSTALLED_APPS:
# settings.py
...
INSTALLED_APPS = list(INSTALLED_APPS) + ['dddp']Add ddp.py to your Django app:
# bookstore/ddp.py
from dddp.api import API, Collection, Publication
from bookstore import models
class Book(Collection):
model = models.Book
class Author(Collection):
model = models.Author
class AllBooks(Publication):
queries = [
models.Author.objects.all(),
models.Book.objects.all(),
]
class BooksByAuthorEmail(Publication):
def get_queries(self, author_email):
return [
models.Author.objects.filter(
email=author_email,
),
models.Book.objects.filter(
author__email=author_email,
),
]
API.register(
[Book, Author, AllBooks, BooksByAuthorEmail]
)Connect your Meteor app to the Django DDP service:
// bookstore.js
if (Meteor.isClient) {
// Connect to Django DDP service
Django = DDP.connect('http://'+window.location.hostname+':8000/');
// Create local collections for Django models received via DDP
Authors = new Mongo.Collection("bookstore.author", {connection: Django});
Books = new Mongo.Collection("bookstore.book", {connection: Django});
// Subscribe to all books by Janet Evanovich
Django.subscribe('BooksByAuthorEmail', 'janet@evanovich.com');
}Start the Django DDP service:
DJANGO_SETTINGS_MODULE=myproject.settings dddpIn a separate terminal, start Meteor (from within your meteor app directory):
meteorContributors
- Tyson Clugg
Author, conceptual design.
- MEERQAT
Project sponsor - many thanks for allowing this to be released under the BSD license!
- David Burles
Expert guidance on how DDP works in Meteor.
- Brenton Cleeland
Great conversations around how collections and publications can limit visibility of published documents to specific users.
- Muhammed Thanish
Making the DDP Test Suite available.
Release history Release notifications | RSS feed
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