How to Implement WebSockets for Real-Time Data Updates in Jinja2 with FastAPI?

How to Get the Updated List of Items in Jinja2 Template Using FastAPI?

In Jinja2 templating, you can render existing data using loops, such as displaying comments on a blog post. However, when new items are added, Jinja2 doesn't natively provide a way to update the list dynamically.

Potential Solution using WebSockets

A common solution for real-time updates in web applications is to use WebSockets. The following Python code provides a WebSocket endpoint:

<code class="python">from fastapi import FastAPI, WebSocket, WebSocketDisconnect
from fastapi.templating import Jinja2Templates

app = FastAPI()
templates = Jinja2Templates(directory="templates")

class ConnectionManager:
    def __init__(self):
        self.active_connections = []

    async def connect(self, websocket: WebSocket):
        await websocket.accept()
        self.active_connections.append(websocket)

    def disconnect(self, websocket: WebSocket):
        self.active_connections.remove(websocket)

    async def broadcast(self, message: str):
        for connection in self.active_connections:
            await connection.send_json(message)

manager = ConnectionManager()</code>

In the index.html template, we establish a WebSocket connection and listen for incoming messages:

<code class="html"><script>
  var ws = new WebSocket("ws://localhost:8000/ws");
  ws.onmessage = function(event) {
    // Handle new data and update UI accordingly
  };
</script></code>

The WebSocket endpoint can then broadcast any updates to connected clients. This allows for a real-time and dynamic display of the updated comments list.

Note:

While WebSockets are a viable solution for this use case, it's important to consider alternative approaches like Alpine JS x-for loops or ReactJS for more complex UI interactions.

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