4Geeks Coding Boilerplates for Junior Developers

Image Upload

Image Upload

Image and file upload using third party:

This article has a video tutorial: https://www.loom.com/share/75d597bfb9c64aa7822cc1d9f9ad1576

🎥 This is a full video tutorial that hopefully will help you use the Cloudinary API to allow users upload images into your application using the traditional <input type="file>.

You can click here to open the example code hosted on this repository.

Don't upload files to your database

Initially, user-uploaded files and images were stored in the same database, but through the years almost every company in the world stopped doing it with a few exceptions, here is why:

  1. Security: if users can upload images, What is stopping them to upload malware? Some malware can be easily hidden within images.
  2. Performance: All of the third party storage services have CDN's available. A CDN can speed your performance in huge amounts, images will load much faster.
  3. Price: storage services like Cloudinary, AWS S3 or Google Storage are really cheap, you will pay only cents or a couple of dollars for the most part.
  4. Easy: It's easier to implement and easier to maintain.


We will be using Cloudinary API to save the images, it's free and 100% integrated with Heroku.


The image upload occurs in 4 steps:

  1. First, you create one html <form> with one <input type="file" /> and use Javascript/React to send the user-selected files to the backend using the fetch function.
  2. The API (backend) will receive that request, retrieve the binary files and send them to the Cloud Storage (Cloudinary).
  3. Cloudinary will respond with a 200 and the URL of the saved image.
  4. The API saves that image URL on the database and responds back to the client.

User profile example

Let's assume you want your users to be able to upload their profile images, for that you will need to have a User model like this:

class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
email = db.Column(db.String(120), unique=True, nullable=False)
profile_image_url = db.Column(db.String(255), unique=False, nullable=True)
password = db.Column(db.String(80), unique=False, nullable=False)
is_active = db.Column(db.Boolean(), unique=False, nullable=False)
def __repr__(self):
return '<User %r>' % self.username
def serialize(self):
return {
"id": self.id,
"email": self.email,
"profile_image_url": self.profile_image_url,
# do not serialize the password, it's a security breach

Note: The user has a property profile_image_url that eventually will contain the user image URL, because that is all we are going to store from the uploaded image, just the URL, the image itself will be hosted by Cloudinary.


On the front end side, we need:

  1. The user id: We need to have the User ID of the logged in user, normally you can store that in the cookies or localStorage, we are going to use localStorage.
  2. Create the form: You have to create a <form> with one <input type="file" /> inside, file inputs are very similar to text but they are made for files (not text), instead of using event.target.value to retrieve its value, you use event.target.files.
  3. Listen to the input change: When the file input changes, (onChange) you have to retrieve all the files that the user picked by using event.target.files, then we store those files in a hooked variable for the near future when the form submission occurs.
  4. Listen to the form submit: Finally, whenever the user decides to submit the form (onSubmit), you fetch to the backend API endpoint those files using the FormData object provided by the browser.
const [files, setFiles] = useState(null);
const uploadImage = evt => {
// we are about to send this to the backend.
console.log("These are the files", files);
let body = new FormData();
body.append("profile_image", files[0]);
const options = {
method: "POST"
// you need to have the user_id in the localStorage
const currentUserId = localStorage.getItem("user_id");
fetch(`${process.env.BACKEND_URL}/user/${currentUserId}/image`, options)
.then(resp => resp.json())
.then(data => console.log("Success!!!!", data))
.catch(error => console.error("ERRORRRRRR!!!", error));
return (
<div className="jumbotron">
<form onSubmit={uploadImage}>
<input type="file" onChange={e => setFiles(e.target.files)} />


The backend is expecting the files from the front end inside the request object, specifically in the request.files property.

import cloudinary
import cloudinary.uploader
@api.route('/user/<int:user_id>/image', methods=['PUT'])
def handle_upload(user_id):
# validate that the front-end request was built correctly
if 'profile_image' in request.files:
# upload file to uploadcare
result = cloudinary.uploader.upload(request.files['profile_image'])
# fetch for the user
user1 = User.query.get(user_id)
# update the user with the given cloudinary image URL
user1.profile_image_url = result['secure_url']
return jsonify(user1.serialize()), 200
raise APIException('Missing profile_image on the FormData')
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