Brings LiveView from Phoenix framework into Django
Project description
Reactor, a LiveView library for Django
Reactor enables you to do something similar to Phoenix framework LiveView using Django Channels.
What's in the box?
This is no replacement for VueJS or ReactJS, or any JavaScript but it will allow you use all the potential of Django to create interactive front-ends. This method has its drawbacks because if connection is lost to the server the components in the front-end go busted until connection is re-established. But also has some advantages, as everything is server side rendered the interface comes already with meaningful information in the first request response, you can use all the power of Django template without limitations, if connection is lost or a component crashes, the front-end will have enough information to rebuild their state in the last good known state.
Installation and setup
Reactor requires Python >=3.9.
Install reactor:
pip install django-reactor
Reactor makes use of django-channels, by default this one uses an InMemory channel layer which is not capable of a real broadcasting, so you might wanna use the Redis one, take a look here: Channel Layers
Add reactor and channels to your INSTALLED_APPS before the Django applications so channels can override the runserver command.
INSTALLED_APPS = [
'reactor',
'channels',
...
]
...
ASGI_APPLICATION = 'project_name.asgi.application'
and modify your project_name/asgi.py file like:
import os
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'project_name.settings')
import django
django.setup()
from channels.auth import AuthMiddlewareStack
from channels.routing import ProtocolTypeRouter, URLRouter
from django.core.asgi import get_asgi_application
from reactor.urls import websocket_urlpatterns
application = ProtocolTypeRouter({
'http': get_asgi_application(),
'websocket': AuthMiddlewareStack(URLRouter(websocket_urlpatterns))
})
Note: Reactor since version 2, autoloads any live.py file in your applications with the hope to find there Reactor Components so they get registered and can be instantiated.
In the templates where you want to use reactive components you have to load the reactor static files. So do something like this so the right JavaScript gets loaded:
{% load reactor %}
<!doctype html>
<html>
<head>
... {% reactor_header %}
</head>
...
</html>
Don't worry if you put this as early as possible, the scripts are loaded using <script defer> so they will be downloaded in parallel with the html, and when all is loaded they are executed.
Simple example of a counter
In your app create a template x-counter.html:
{% load reactor %}
<div {% tag_header %}>
{{ amount }}
<button {% on 'click' 'inc' %}>+</button>
<button {% on 'click' 'dec' %}>-</button>
<button {% on 'click' 'set_to' amount=0 %}>reset</button>
</div>
Anatomy of a template: each component should be a custom web component that inherits from HTMLElement. They should have an id so the backend knows which instance is this one and a state attribute with the necessary information to recreate the full state of the component on first render and in case of re-connection to the back-end.
Render things as usually, so you can use full Django template language, trans, if, for and so on. Just keep in mind that the instance of the component is referred as this.
Forwarding events to the back-end: Notice that for event binding in-line JavaScript is used on the event handler of the HTML elements. How does this work? When the increment button receives a click event send(this, 'inc') is called, send is a reactor function that will look for the parent custom component and will dispatch to it the inc message, or the set_to message and its parameters {amount: 0}. The custom element then will send this message to the back-end, where the state of the component will change and then will be re-rendered back to the front-end. In the front-end morphdom (just like in Phoenix LiveView) is used to apply the new HTML.
Now let's write the behavior part of the component in live.py:
from reactor.component import Component
class XCounter(Component):
_template_name = 'x-counter.html'
amount: int = 0
async def recv_inc(self):
self.amount += 1
async def recv_dec(self):
self.amount -= 1
async def recv_set_to(self, amount: int):
self.amount = amount
Let's now render this counter, expose a normal view that renders HTML, like:
def index(request):
return render(request, 'index.html')
And the index template being:
{% load reactor %}
<!doctype html>
<html>
<head>
.... {% reactor_header %}
</head>
<body>
{% component 'XCounter' %}
<!-- or passing an initial state -->
{% component 'XCounter' amount=100 %}
</body>
</html>
Don't forget to update your urls.py to call the index view.
Persisting the state of the Counter in the URL as a GET parameter
Add:
...
class SearchList(Component):
query: str = ""
@classmethod
def new(cls, reactor: ReactorMeta, **kwargs):
# read the query parameter and initialize the object with that parameter
kwargs.setdefault("query", reactor.params.get("query", ""))
return cls(reactor=reactor, **kwargs)
async def filter_results(self, query: str):
self.query = query
# update the query string in the browser
self.reactor.params["query"] = query
...
This will make that everytime that method gets called the query string on the browser will get updated to include "query=blahblah". Never replace the self.reactor.params, mutate it instead.
Here is another example, suppose you have a list of items that can be expanded, like nodes in a tree view:
class Node(Component):
name: str
expanded: bool = False
@classmethod
def new(cls, reactor: ReactorMeta, id: str, **kwargs):
kwargs["expanded"] = id in reactor.params.get("expanded.json", [])
return cls(reactor=reactor, id=id, **kwargs)
async def toggle_expanded(self):
self.expanded = not self.expanded
expanded = self.reactor.params.setdefault("expanded.json", [])
if self.expanded:
expanded.append(self.id)
elif self.id in expanded:
expanded.remove(self.id)
Here expanded.json is a list of the expanded nodes. Notice the .json this indicates that the value of this key should be encoded/decoded to/from JSON, so just put there JSON serializable stuff.
Settings:
Default settings of reactor are:
from reactor.schemas import AutoBroadcast
REACTOR = {
"TRANSPILER_CACHE_SIZE": 1024,
"USE_HTML_DIFF": True,
"USE_HMIN": False,
"BOOST_PAGES": False,
"TRANSPILER_CACHE_NAME": "reactor:transpiler",
"AUTO_BROADCAST": AutoBroadcast(
# model-a
model: bool = False
# model-a.1234
model_pk: bool = False
# model-b.9876.model-a-set
related: bool = False
# model-b.9876.model-a-set
# model-a.1234.model-b-set
m2m: bool = False
# this is a set of tuples of ('app_label', 'ModelName')
# to subscribe for the auto broadcast
senders: set[tuple[str, str]] = Field(default_factory=set)
),
}
TRANSPILER_CACHE_SIZE: this is the size of an LRU dict used to cache javascript event halder transpilations.USE_HTML_DIFF: when enabled usesdifflibto create diffs to patch the front-end, reducing bandwidth. If disabled it sends the full HTML content every time.REACTOR_USE_HMIN: when enabled and django-hmin is installed will use it to minified the HTML of the components and save bandwidth.AUTO_BROADCAST: Controls which signals are sent toComponent.mutationwhen a model is mutated.
Back-end APIs
Template tags and filters of reactor library
{% reactor_header %}: that includes the necessary JavaScript to make this library work. ~10Kb of minified JS, compressed with gz or brotli.{% component 'Component' param1=1 param2=2 %}: Renders a component by its name and passing whatever parameters you put there to theXComponent.newmethod that constructs the component instance.{% on 'click' 'event_handler' param1=1 param2=2 %}: Binds an event handler with paramters to some event. Look at Event binding in the front-endcond: Allows simple conditional presence of a string:{% cond {'hidden': is_hidden } %}.class: Use it to handle conditional classes:<div {% class {'nav_bar': True, 'hidden': is_hidden} %}></div>.
Component live cycle
Initialization & Rendering
This happens when in a "normal" template you include a component.
{% component 'Component' param1=1 param2=2 %}
This passes those parameter there to Component.new that should return the component instance and then the component get's rendered in the template and is sent to the client.
Joins
When the component arrives to the front-end it "joins" the backend. Sends it's serialized state to the backend which rebuilds the component and calls Component.joined.
After that the component is rendered and the render is sent to the front-end. Why? Because could be that the client was online while some change in the backend happened and the component needs to be updated.
User events
When a component or its parent has joined it can send user events to the client. Using the on template tag, this events are sent to the backend and then the componet is rendered again.
Subscriptions
Every time a component joins or responds to an event the Componet._subscriptions set is reviewed to check if the component subscribes or not to some channel.
- In case a mutation in a model occurs
Component.mutation(channel: str, action: reactor.auto_broadcast.Action, instance: Model)will be called. - In case you broadcast a message using
reactor.component.broadcast(channel, **kwargs)this message will be sent to any component subscribed tochannelusing the methodComponent.notification(channel, **kwargs).
Disconnection
If the component is destroyed using the Component.destroy or just desapears from the front-end it is removed from the backend. If the the websocket closes all components in that connection are removed from the backend and the state of those componets stay just in the front-end in the seralized form awaiting for the front-end to join again.
Component API
Each component is a Pydantic model so it can serialize itself. I would advice not to mess with the __init__ method.
Instead use the class method new to create the instance.
Rendering
_template_name: Contains the path of the template of the component._exclude_fields: (default:{"user", "reactor"}) Which fields to exclude from state serialization during rendering
Subscriptions
_subscriptions: (default:set()) Defines which channels is this component subscribed to.mutation(channel, action, instance)Called when autobroadcast is enabled and a model you are subscribed to changes.notification(channel, **kwargs)Called whenreactor.component.broadcast(channel, **kwargs)is used to send an arbitrary notification to components.
Actions
destroy(): Removes the component from the interface.focus_on(selector: str): Makes the front-end look for thatselectorand run.focus()on it.skip_render(): Prevents the component from being rendered once.send_render(): Send a signal to request render the component ahead of time.dom(_action: DomAction, id: str, component_or_template, **kwargs): Can append, prepend, insert befor or after certain HTMLElement ID in the dom, the component or template, rendered using thekwargs.freeze(): Prevents the component from being rendered again.deffer(f, *args, **kwargs): Send a message to the current event to be executed after the current function is executed.reactor.redirect_to(to, **kwargs): Changes the URL of the front-end and triggers a page load for that new URLreactor.replace_to(to, **kwargs): Changes the current URL for another one.reactor.push_to(to, **kwargs): Changs the URL of the front-end adding a new history entry but does not fetch the new URL from the backend.reactor.send(_channel: str, _topic: str, **kwargs): Sends a message over a channel.
Front-end APIs
reactor.send(element, name, args): Sends a reactor user event toelement, wherenameis the event handler andargsis a JS object containing the implicit arguments of the call.
Event binding in the front-end
Look at this:
<button {% on "click.prevent" "submit" %}>Submit</button>
Syntax: {% on [] %}
The format for event and modifiers is @<event>[.modifier1][.modifier2][.modifier2-argument1][.modifier2-argument2]
Examples:
{% on "click.ctrl" "decrement" %}>: Clicking with Ctrl pressed calls "decrement".{% on "click" "increment" amount=1 %}>: Clicking calls "increment" passingamount=1as argument.
Misc:
-
event: is the name of the HTMLElement event:click,blur,change,keypress,keyup,keydown... -
modifier: can be concatenated after the event name and represent actions or conditions to be met before the event execution. This is very similar as how VueJS does event binding:Available modifiers are:
inlinejs: takes the next "event handler" argument as literal JS code.prevent: callsevent.preventDefault()stop: callsevent.StopPropagation()ctrl,alt,shift,meta: continues processing the event if any of those keys is presseddebounce: debounces the event, it needs a delay in milliseconds. Example:keypress.debounce.100.key.<keycode>: continues processing the event if the key withkeycodeis pressedenter: alias forkey.entertab: alias forkey.tabdelete: alias forkey.deletebackspace: alias forkey.backspacespace: alias forkey.up: alias forkey.arrowupdown: alias forkey.arrowdownleft: alias forkey.arrowleftright: alias forkey.arrowright
Event arguments
Reactor sends the implicit arguments you pass on the on template tag, but also sends implicit arguments.
The implicit arguments are taken from the form the element handling the event is in or from the whole component otherwise.
Examples:
Here any event inside that component will have the implicit argument x being send to the backend.
<div {% tag-header %}>
<input name="x"/>
<button {% on "click" "submit" %}>Send</button>
</div>
Here any submit_x will send x, and submit_y will send just y.
<div {% tag-header %}>
<input name="x"/>
<button {% on "click" "submit_x" %}>Send</button>
<form>
<input name="y"/>
<button {% on "click.prevent" "submit_y" %}>Send</button>
</form>
</div>
Event handlers in the back-end
Given:
<button {% on 'click 'inc' amount=2 %}>Increment</button>
You will need an event handler in that component in the back-end:
async def inc(self, amount: int):
...
It is good if you annotate the signature so the types are validated and converted if they have to be.
More complex components
I made a TODO list app using models that signals from the model to the respective channels to update the interface when something gets created, modified or deleted.
This example contains nested components and some more complex interactions than a simple counter, the app is in the /tests/ directory.
Development & Contributing
Clone the repo and create a virtualenv or any other contained environment, get inside the repo directory, build the development environment and the run tests.
git clone git@github.com:edelvalle/reactor.git
cd reactor
make install
make test
If you want to run the included Django project used for testing do:
make
cd tests
python manage.py runserver
Enjoy!
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