How to submit HTML form <input> value using FastAPI and Jinja2 Templates?
Question:
I am facing the following issue while trying to pass a value from an HTML form <input> element to the form’s action attribute and send it to the FastAPI server.
This is how the Jinja2 (HTML) template is loaded:
# Test TEMPLATES
@app.get("/test",response_class=HTMLResponse)
async def read_item(request: Request):
return templates.TemplateResponse("index.html", {"request": request})
My HTML form:
<form action="/disableSubCategory/{{subCatName}}">
<label for="subCatName">SubCategory:</label><br>
<input type="text" id="subCatName" name="subCatName" value=""><br>
<input type="submit" value="Disable">
</form>
My FastAPI endpoint to be called in the form action:
# Disable SubCategory
@app.get("/disableSubCategory/{subCatName}")
async def deactivateSubCategory(subCatName: str):
disableSubCategory(subCatName)
return {"message": "SubCategory [" + subCatName + "] Disabled"}
The error I get:
"GET /disableSubCategory/?subCatName=Barber HTTP/1.1" 404 Not Found
What I am trying to achieve is the following FastAPI call:
/disableSubCategory/{subCatName} ==> "/disableSubCategory/Barber"
Anyone who could help me understand what I am doing wrong?
Thanks.
Leo
Answers:
Option 1
You can have the category name defined as Form parameter in the backend, and submit a POST request from the frontend using an HTML <form>, as described in Method 1 of this answer.
app.py
from fastapi import FastAPI, Form, Request
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
app = FastAPI()
templates = Jinja2Templates(directory='templates')
@app.post('/disable')
def disable_cat(cat_name: str = Form(...)):
return f'{cat_name} category has been disabled.'
@app.get('/', response_class=HTMLResponse)
def main(request: Request):
return templates.TemplateResponse('index.html', {'request': request})
templates/index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<h1>Disable a category</h1>
<form method="post" action="/disable">
<label for="cat_name">Enter a category name to disable:</label><br>
<input type="text" id="cat_name" name="cat_name">
<input class="submit" type="submit" value="Submit">
</form>
</body>
</html>
Option 2
You can have the category name declared as query parameter in your endpoint, and in the frontend use a similar approach to the one demonstrated in your question to convert the value form the form <input> element into a query parameter, and then add it to the query string of the URL (in the action attribute).
Note that the below uses a GET request in contrast to the above (in this case, you need to use @app.get() in the backend and <form method="get" ... in the frontend, which is the default method anyway). Beware that most browsers cache GET requests (i.e., saved in browser’s history), thus making them less secure compared to POST, as the data sent are part of the URL and visible to anyone who has access to the device. Thus, GET method should not be used when sending passwords or other sensitive information.
app.py
from fastapi import FastAPI, Request
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
app = FastAPI()
templates = Jinja2Templates(directory='templates')
@app.get('/disable')
def disable_cat(cat_name: str):
return f'{cat_name} category has been disabled.'
@app.get('/', response_class=HTMLResponse)
def main(request: Request):
return templates.TemplateResponse('index.html', {'request': request})
templates/index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<h1>Disable a category</h1>
<form method="get" id="myForm" action='/disable{{ cat_name }}'>
<label for="cat_name">Enter a category name to disable:</label><br>
<input type="text" id="cat_name" name="cat_name">
<input class="submit" type="submit" value="Submit">
</form>
</body>
</html>
If you instead would like to use a POST request—which is a little safer than GET, as the parameters are not stored in the browser’s history, and which makes more sense when updating content/state on the server, compared to GET that should be used when requesting (not modifying) data—you can define the FastAPI endpoint with @app.post() and replace the above template with the below (similar to Method 2 of this answer), which submits the form using POST method after transforming the form data into query parameters:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("myForm").addEventListener("submit", function (e) {
var myForm = document.getElementById('myForm');
var qs = new URLSearchParams(new FormData(myForm)).toString();
myForm.action = '/disable?' + qs;
});
});
</script>
</head>
<body>
<h1>Disable a category</h1>
<form method="post" id="myForm">
<label for="cat_name">Enter a category name to disable:</label><br>
<input type="text" id="cat_name" name="cat_name">
<input class="submit" type="submit" value="Submit">
</form>
</body>
</html>
Option 3
You can still have it defined as path parameter, and use JavaScript in the frontend to modify the action attribute of the <form>, by passing the value of the form <input> element as path parameter to the URL, similar to what has been described earlier.
app.py
from fastapi import FastAPI, Request
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
app = FastAPI()
templates = Jinja2Templates(directory='templates')
@app.post('/disable/{name}')
def disable_cat(name: str):
return f'{name} category has been disabled.'
@app.get('/', response_class=HTMLResponse)
def main(request: Request):
return templates.TemplateResponse('index.html', {'request': request})
templates/index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("myForm").addEventListener("submit", function (e) {
var myForm = document.getElementById('myForm');
var catName = document.getElementById('catName').value;
myForm.action = '/disable/' + catName;
});
});
</script>
</head>
<body>
<h1>Disable a category</h1>
<form method="post" id="myForm">
<label for="catName">Enter a category name to disable:</label><br>
<input type="text" id="catName" name="catName">
<input class="submit" type="submit" value="Submit">
</form>
</body>
</html>
Option 4
If you would like to prevent the page from reloading/redirecting when hitting the submit button of the HTML <form> and rather get the results in the same page, you can use Fetch API, a JavaScript interface/library, to make an asynchronous HTTP request, similar to this answer, as well as this answer and this answer. Additionally, one can call the Event.preventDefault() function, as described in this answer, to prevent the default action. The example below is based on the previous option (i.e., Option 3); however, the same approach below (i.e., making an asynchronous HTTP request) can also be used for Options 1 & 2 demonstrated earlier, if you would like to keep the browser from refreshing the page on <form> submission.
app.py
from fastapi import FastAPI, Request
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
app = FastAPI()
templates = Jinja2Templates(directory='templates')
@app.post('/disable/{name}')
def disable_cat(name: str):
return f'{name} category has been disabled.'
@app.get('/', response_class=HTMLResponse)
def main(request: Request):
return templates.TemplateResponse('index.html', {'request': request})
templates/index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("myForm").addEventListener("submit", function (e) {
e.preventDefault() // Cancel the default action
var catName = document.getElementById('catName').value;
fetch('/disable/' + catName, {
method: 'POST',
})
.then(resp => resp.text()) // or, resp.json(), etc.
.then(data => {
document.getElementById("response").innerHTML = data;
})
.catch(error => {
console.error(error);
});
});
});
</script>
</head>
<body>
<h1>Disable a category</h1>
<form id="myForm">
<label for="catName">Enter a category name to disable:</label><br>
<input type="text" id="catName" name="catName">
<input class="submit" type="submit" value="Submit">
</form>
<div id="response"></div>
</body>
</html>
Just to provide you a feedback and keep track about the solution I’ve put in place.
As mentioned by @Chris, I went to the proposed solution 3.
Please find below my new code:
== FastAPI ==
# Test TEMPLATES
@app.get("/test",response_class=HTMLResponse)
async def read_item(request: Request):
return templates.TemplateResponse("index.html", {"request": request})
# Disable SubCategory
@app.post("/disableSubCategory/{subCatName}")
async def deactivateSubCategory(subCatName: str):
disableSubCategory(subCatName)
return {"message": "Sub-Category [" + subCatName + "] Disabled"}
# Enable SubCategory
@app.post("/enableSubCategory/{subCatName}")
async def activateSubCategory(subCatName: str):
enableSubCategory(subCatName)
return {"message": "Sub-Category [" + subCatName + "] Enabled"}
== HTML ==
<html>
<head>
<title>Item Details</title>
<link href="{{ url_for('static', path='/styles.css') }}" rel="stylesheet">
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("disableSubCategory").addEventListener("submit", function (e) {
var myForm = document.getElementById('disableSubCategory');
var disableSubCatName = document.getElementById('id_disableSubCategory').value;
myForm.action = '/disableSubCategory/' + disableSubCatName;
});
});
</script>
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("enableSubCategory").addEventListener("submit", function (e) {
var myForm2 = document.getElementById('enableSubCategory');
var enableSubCatName = document.getElementById('id_enableSubCategory').value;
myForm2.action = '/enableSubCategory/' + enableSubCatName;
});
});
</script>
</head>
<body>
<form id="disableSubCategory" enctype="multipart/form-data" method="post">
<label for="subCatName">SubCategory:</label><br>
<input type="text" id="id_disableSubCategory" value=""><br>
<input type="submit" value="Disable" id="disable">
</form>
<form id="enableSubCategory" enctype="multipart/form-data" method="post">
<label for="subCatName">SubCategory:</label><br>
<input type="text" id="id_enableSubCategory" value=""><br>
<input type="submit" value="Enable" id="enable">
</form>
</body>
</html>
I am facing the following issue while trying to pass a value from an HTML form <input> element to the form’s action attribute and send it to the FastAPI server.
This is how the Jinja2 (HTML) template is loaded:
# Test TEMPLATES
@app.get("/test",response_class=HTMLResponse)
async def read_item(request: Request):
return templates.TemplateResponse("index.html", {"request": request})
My HTML form:
<form action="/disableSubCategory/{{subCatName}}">
<label for="subCatName">SubCategory:</label><br>
<input type="text" id="subCatName" name="subCatName" value=""><br>
<input type="submit" value="Disable">
</form>
My FastAPI endpoint to be called in the form action:
# Disable SubCategory
@app.get("/disableSubCategory/{subCatName}")
async def deactivateSubCategory(subCatName: str):
disableSubCategory(subCatName)
return {"message": "SubCategory [" + subCatName + "] Disabled"}
The error I get:
"GET /disableSubCategory/?subCatName=Barber HTTP/1.1" 404 Not Found
What I am trying to achieve is the following FastAPI call:
/disableSubCategory/{subCatName} ==> "/disableSubCategory/Barber"
Anyone who could help me understand what I am doing wrong?
Thanks.
Leo
Option 1
You can have the category name defined as Form parameter in the backend, and submit a POST request from the frontend using an HTML <form>, as described in Method 1 of this answer.
app.py
from fastapi import FastAPI, Form, Request
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
app = FastAPI()
templates = Jinja2Templates(directory='templates')
@app.post('/disable')
def disable_cat(cat_name: str = Form(...)):
return f'{cat_name} category has been disabled.'
@app.get('/', response_class=HTMLResponse)
def main(request: Request):
return templates.TemplateResponse('index.html', {'request': request})
templates/index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<h1>Disable a category</h1>
<form method="post" action="/disable">
<label for="cat_name">Enter a category name to disable:</label><br>
<input type="text" id="cat_name" name="cat_name">
<input class="submit" type="submit" value="Submit">
</form>
</body>
</html>
Option 2
You can have the category name declared as query parameter in your endpoint, and in the frontend use a similar approach to the one demonstrated in your question to convert the value form the form <input> element into a query parameter, and then add it to the query string of the URL (in the action attribute).
Note that the below uses a GET request in contrast to the above (in this case, you need to use @app.get() in the backend and <form method="get" ... in the frontend, which is the default method anyway). Beware that most browsers cache GET requests (i.e., saved in browser’s history), thus making them less secure compared to POST, as the data sent are part of the URL and visible to anyone who has access to the device. Thus, GET method should not be used when sending passwords or other sensitive information.
app.py
from fastapi import FastAPI, Request
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
app = FastAPI()
templates = Jinja2Templates(directory='templates')
@app.get('/disable')
def disable_cat(cat_name: str):
return f'{cat_name} category has been disabled.'
@app.get('/', response_class=HTMLResponse)
def main(request: Request):
return templates.TemplateResponse('index.html', {'request': request})
templates/index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<h1>Disable a category</h1>
<form method="get" id="myForm" action='/disable{{ cat_name }}'>
<label for="cat_name">Enter a category name to disable:</label><br>
<input type="text" id="cat_name" name="cat_name">
<input class="submit" type="submit" value="Submit">
</form>
</body>
</html>
If you instead would like to use a POST request—which is a little safer than GET, as the parameters are not stored in the browser’s history, and which makes more sense when updating content/state on the server, compared to GET that should be used when requesting (not modifying) data—you can define the FastAPI endpoint with @app.post() and replace the above template with the below (similar to Method 2 of this answer), which submits the form using POST method after transforming the form data into query parameters:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("myForm").addEventListener("submit", function (e) {
var myForm = document.getElementById('myForm');
var qs = new URLSearchParams(new FormData(myForm)).toString();
myForm.action = '/disable?' + qs;
});
});
</script>
</head>
<body>
<h1>Disable a category</h1>
<form method="post" id="myForm">
<label for="cat_name">Enter a category name to disable:</label><br>
<input type="text" id="cat_name" name="cat_name">
<input class="submit" type="submit" value="Submit">
</form>
</body>
</html>
Option 3
You can still have it defined as path parameter, and use JavaScript in the frontend to modify the action attribute of the <form>, by passing the value of the form <input> element as path parameter to the URL, similar to what has been described earlier.
app.py
from fastapi import FastAPI, Request
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
app = FastAPI()
templates = Jinja2Templates(directory='templates')
@app.post('/disable/{name}')
def disable_cat(name: str):
return f'{name} category has been disabled.'
@app.get('/', response_class=HTMLResponse)
def main(request: Request):
return templates.TemplateResponse('index.html', {'request': request})
templates/index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("myForm").addEventListener("submit", function (e) {
var myForm = document.getElementById('myForm');
var catName = document.getElementById('catName').value;
myForm.action = '/disable/' + catName;
});
});
</script>
</head>
<body>
<h1>Disable a category</h1>
<form method="post" id="myForm">
<label for="catName">Enter a category name to disable:</label><br>
<input type="text" id="catName" name="catName">
<input class="submit" type="submit" value="Submit">
</form>
</body>
</html>
Option 4
If you would like to prevent the page from reloading/redirecting when hitting the submit button of the HTML <form> and rather get the results in the same page, you can use Fetch API, a JavaScript interface/library, to make an asynchronous HTTP request, similar to this answer, as well as this answer and this answer. Additionally, one can call the Event.preventDefault() function, as described in this answer, to prevent the default action. The example below is based on the previous option (i.e., Option 3); however, the same approach below (i.e., making an asynchronous HTTP request) can also be used for Options 1 & 2 demonstrated earlier, if you would like to keep the browser from refreshing the page on <form> submission.
app.py
from fastapi import FastAPI, Request
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
app = FastAPI()
templates = Jinja2Templates(directory='templates')
@app.post('/disable/{name}')
def disable_cat(name: str):
return f'{name} category has been disabled.'
@app.get('/', response_class=HTMLResponse)
def main(request: Request):
return templates.TemplateResponse('index.html', {'request': request})
templates/index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("myForm").addEventListener("submit", function (e) {
e.preventDefault() // Cancel the default action
var catName = document.getElementById('catName').value;
fetch('/disable/' + catName, {
method: 'POST',
})
.then(resp => resp.text()) // or, resp.json(), etc.
.then(data => {
document.getElementById("response").innerHTML = data;
})
.catch(error => {
console.error(error);
});
});
});
</script>
</head>
<body>
<h1>Disable a category</h1>
<form id="myForm">
<label for="catName">Enter a category name to disable:</label><br>
<input type="text" id="catName" name="catName">
<input class="submit" type="submit" value="Submit">
</form>
<div id="response"></div>
</body>
</html>
Just to provide you a feedback and keep track about the solution I’ve put in place.
As mentioned by @Chris, I went to the proposed solution 3.
Please find below my new code:
== FastAPI ==
# Test TEMPLATES
@app.get("/test",response_class=HTMLResponse)
async def read_item(request: Request):
return templates.TemplateResponse("index.html", {"request": request})
# Disable SubCategory
@app.post("/disableSubCategory/{subCatName}")
async def deactivateSubCategory(subCatName: str):
disableSubCategory(subCatName)
return {"message": "Sub-Category [" + subCatName + "] Disabled"}
# Enable SubCategory
@app.post("/enableSubCategory/{subCatName}")
async def activateSubCategory(subCatName: str):
enableSubCategory(subCatName)
return {"message": "Sub-Category [" + subCatName + "] Enabled"}
== HTML ==
<html>
<head>
<title>Item Details</title>
<link href="{{ url_for('static', path='/styles.css') }}" rel="stylesheet">
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("disableSubCategory").addEventListener("submit", function (e) {
var myForm = document.getElementById('disableSubCategory');
var disableSubCatName = document.getElementById('id_disableSubCategory').value;
myForm.action = '/disableSubCategory/' + disableSubCatName;
});
});
</script>
<script>
document.addEventListener('DOMContentLoaded', (event) => {
document.getElementById("enableSubCategory").addEventListener("submit", function (e) {
var myForm2 = document.getElementById('enableSubCategory');
var enableSubCatName = document.getElementById('id_enableSubCategory').value;
myForm2.action = '/enableSubCategory/' + enableSubCatName;
});
});
</script>
</head>
<body>
<form id="disableSubCategory" enctype="multipart/form-data" method="post">
<label for="subCatName">SubCategory:</label><br>
<input type="text" id="id_disableSubCategory" value=""><br>
<input type="submit" value="Disable" id="disable">
</form>
<form id="enableSubCategory" enctype="multipart/form-data" method="post">
<label for="subCatName">SubCategory:</label><br>
<input type="text" id="id_enableSubCategory" value=""><br>
<input type="submit" value="Enable" id="enable">
</form>
</body>
</html>