How to redirect the user back to the home page using FastAPI, after submitting an HTML form?

from fastapi import FastAPI, Form from fastapi.responses import Response import json from jinja2 import Template app = FastAPI() # The page with the table @app.get('/') def index(): students = get_students() # Get a list of students with open('templates/students.html', 'r', encoding='utf-8') as file: html = file.read() template = Template(html) # Creating a template with a table # Loading a template return Response(template.render(students=students), media_type='text/html') # Page with forms for adding a new entry @app.get('/add_student') def add_student_page(): with open('templates/add_student.html', 'r', encoding='utf-8') as file: html = file.read() # Loading a page return Response(html, media_type='text/html') # Processing forms and adding a new entry @app.post('/add') def add(name: str = Form(...), surname: str = Form(...), _class: str = Form(...)): add_student(name, surname, _class) # Adding student data # ???

To start with, in cases where you return Jinja2 templates, you should return a TemplateResponse, as shown in the documentation. To redirect the user to a specific page, you can use RedirectResponse. Since you do that through a POST (and not GET) method, as shown in your example, a 405 (Method Not Allowed) error would be thrown. However, thanks to @tiangolo, you can change the response status code to status_code=status.HTTP_303_SEE_OTHER, and the issue will then be resolved (please have a look at this answer and this answer for more details). A working example is given below.

In case you needed to pass additional path and/or query parameters to your endpoint, please have a look at this and this answer as well.

In case you had to do the same, using Fetch API instead of HTML <form>, please have a look at this answer.

Working Example

app.py

from fastapi import FastAPI, Request, Form, status
from fastapi.templating import Jinja2Templates
from fastapi.responses import RedirectResponse

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

# replace with your own get_students() method
def get_students():
    return ["a", "b", "c"]

@app.post('/add')
async def add(request: Request, name: str = Form(...), surname: str = Form(...), _class: str = Form(...)):
    # add_student(name, surname, _class)  # Adding student data
    redirect_url = request.url_for('index')    
    return RedirectResponse(redirect_url, status_code=status.HTTP_303_SEE_OTHER)    

@app.get('/add_student')
async def add_student_page(request: Request):
    return templates.TemplateResponse("add_student.html", {"request": request})

@app.get('/')
async def index(request: Request):
    students = get_students()  # Get a list of students
    return templates.TemplateResponse("index.html", {"request": request, "students": students})

templates/index.html

<!DOCTYPE html>
<html>
   <body>
      <h1>Students: {{ students }}</h1>
   </body>
</html>

templates/add_student.html

<!DOCTYPE html>
<html>
   <body>
      <form action="http://127.0.0.1:8000/add" method="POST">
         name : <input type="text" name="name"><br>
         surname : <input type="text" name="surname"><br>
         class : <input type="text" name="_class"><br>
         <input type="submit" value="submit">
      </form>
   </body>
</html>

Working Example

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