Getting Updated List of Items in Jinja2 Template Using FastAPI
In this tutorial, we demonstrate how to implement a real-time chat application using FastAPI and Jinja2 for dynamic updates of comment lists. The application leverages WebSockets to establish a bidirectional communication channel between the server and multiple clients.
Problem:
Imagine building a blog comment system where new comments need to be dynamically added to the frontend without requiring a page refresh. Jinja2 templates are used to render existing comments on the page, but a mechanism is needed to retrieve and display newly added comments in real-time.
Solution:
To achieve this functionality, we introduce WebSockets, a technology that allows for real-time, bidirectional communication over a single TCP connection. By implementing WebSockets with FastAPI and Jinja2, we can establish a persistent connection between the server and the client, enabling the server to broadcast new comments to all connected clients in real-time.
Implementing WebSockets:
To set up WebSockets in FastAPI, we create a WebSocket endpoint that handles incoming connections and establishes a dedicated connection for each client. The following code shows our WebSocket endpoint:
<code class="python">@app.websocket("/ws") async def websocket_endpoint(websocket: WebSocket): await manager.connect(websocket) try: while True: data = await websocket.receive_json() comments.append(Comment(data['author'], data['content'])) await manager.broadcast(data) except (WebSocketDisconnect, ConnectionClosed): manager.disconnect(websocket)</code>
In this code:
Updating the Jinja2 Template:
To display the updated comments in the Jinja2 template, we use JavaScript and WebSockets to listen for incoming messages from the server and dynamically add new comments to the page. In our index.html template, we include the following JavaScript code:
<code class="html"><script> var ws = new WebSocket("ws://localhost:8000/ws"); ws.onmessage = function(event) { var comments = document.getElementById('comments'); var comment = document.createElement('li'); var jsonObj = JSON.parse(event.data); var authorNode = document.createElement('h3'); authorNode.innerHTML = jsonObj.author; var contentNode = document.createElement('p'); contentNode.innerHTML = jsonObj.content; comment.appendChild(authorNode); comment.appendChild(contentNode); comments.appendChild(comment); }; </script></code>
This JavaScript code:
Conclusion
By integrating WebSockets with FastAPI and Jinja2, we have implemented a dynamic comment system that allows for real-time updates. This technique can be applied to various scenarios where you need to send and receive messages or data between clients and a server in real-time, providing a highly interactive and responsive user experience.
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