I just started using FastAPI for a home project and needed to pass back a dynamic number of values from a form rendered with jinja...

Dynamic Values

The jinja templating for rendering HTML based on something like a python iterable is nice and easy

data is the result of a database query, and item is each row, so the dot notation is the value of each column basically in that row

<form method="post">
  {% for item in data %}
    <div class="form-check ">
        <input class="form-check-input"  name="item_{{ item.id }}" id="{{ item.name }}" value="{{ item.id }}" type="checkbox">
        <label class="form-check-label" for="{{ item.id }}" > Label for: {{ item.name }} </label>
    </div>
  {% endfor %}

<button type="submit" class="submit btn btn-xl btn-outline-danger" >Remove</button>
</form>

This form generates a row with a checkbox for every item in data (in my case each item is an existing row in my table). it?

The way to pass back all those values is pretty straight forward (after hours of messing around that is!)

# I hate it when tutorials don't show ALL relevant pieces to the blurb
import starlette.status as status
from fastapi import APIRouter, Depends, Form, Request
from fastapi.encoders import jsonable_encoder
from fastapi.responses import HTMLResponse, RedirectResponse
from fastapi.templating import Jinja2Templates
from sqlalchemy.orm import Session

from app.session.session import create_get_session

router = APIRouter()
templates = Jinja2Templates(directory="templates/")

@router.post("/my_route/do_something_with_form", response_class=HTMLResponse)
async def delete_rows(
    request: Request,
    db: Session = Depends(create_get_session),
):
    form_data = await request.get_form()
    data = jsonable_encoder(form_data)
    # data = {"item_1": 1, "item_2": 2, ... "item_N": N}
    return RedirectResponse("/", status_code=status.HTTP_302_FOUND)

We await request.get_form() and after encoding the data we get a dictionary with key/value pairs of the name/value from the form!

This took me quite a long time to figure out in part because most of the Google-able resources are still on Flask...