- Create an API with Flask for a React frontend application.
So far, we've seen how to build a Flask API and perform various CRUD actions using SQLAlchemy. In this lab, you'll work on creating an API in Flask once more โ but this time, you'll also have code for a React frontend application, so you can get a taste of full-stack development!
This project is separated into two applications:
- A React frontend, in the
client
directory. - A Flask backend, in the
server
directory
All of the features for the React frontend are built out, and we have a simple
json-server
API that you can run to see what the completed version of the app
will look like. Your main goal with this lab is to build out a Flask API
server to replace json-server
, so most of your coding will be done in the
backend.
Let's take a quick tour of what we have so far.
To get started, cd
into the chatterbox-client
directory. Then run:
$ npm install
$ npm run server
This will install the React project dependencies, and run a demo API server
using json-server
. Next, run this in a new terminal:
$ npm start
Then visit http://localhost:3000 in the browser and interact with the demo application to get a sense of its features.
Here's a demo of the what the React app should look like when using
json-server
as the API:
Take a look at the components provided in the chatterbox-client
directory.
Explore the code and pay special attention to where the React application is
interacting with json-server
. Where are the fetch
requests being written?
What routes are needed to handle these requests? What HTTP verbs? What data is
being sent in the body of the requests?
Once you've familiarized yourself yourself with the code, turn off json-server
with control + c
in the terminal where we ran npm run server
(you can keep
the React application running, though). Next, let's see what we have in the
backend.
In another terminal, cd
into the chatterbox-server
directory, and run
pipenv install && pipenv shell
to install the dependencies and enter your
virtual environment.
In this directory, you're given a bare-bones template for a Flask API application. It should look familiar to other Flask labs you've seen and has all the code set up so you can focus on building out your model and API routes.
You'll be responsible for:
- Creating a model and migrations.
- Setting up the necessary routes to handle requests.
- Performing CRUD actions with SQLAlchemy.
- Sending the necessary JSON data in the responses.
The only new code for the server is the Flask CORS extension. This extension provides some Flask middleware which we need to configure so that applications running in the browser, like our React client, can make requests to the backend.
If we didn't use this gemextension, any requests from our React frontend in the browser would result in an error message like this:
Access to fetch at 'http://localhost:5000/messages' from origin
'http://localhost:3000' has been blocked by CORS policy: No
'Access-Control-Allow-Origin' header is present on the requested resource. If an
opaque response serves your needs, set the request's mode to 'no-cors' to fetch
the resource with CORS disabled.
The reason for this warning message is due to a browser security feature known as Cross-Origin Resource Sharing (CORS). When we use JavaScript from one domain (aka origin) to make a request to a server on a different domain, the default behavior of the browser is to block those requests from going through.
For example, if I own the website definitelynotahacker.com
, I can't use
JavaScript to make a network request to api.yourbankaccount.com
, unless
api.yourbankaccount.com
explicitly gives permission to my website.
To give that permission, any server that we want to make requests to using JavaScript must add some special headers to the response that tell the browser that the request was permitted.
Here's what the CORS configuration looks like (in the server/app.py
file):
# server/app.py
from flask import Flask
from flask_cors import CORS
app = Flask(__name__)
CORS(app)
You don't have to make any changes to this configuration to complete this lab, but CORS warnings are a very common thing to encounter in web development, so next time you see them, you'll know what this means!
NOTE: There may come a time when you want CORS configured for some routes but not others. You can specify these with the optional
resources
argument or by instead using the@cross_origin()
decorator on specific routes.
Work through the deliverables below. There are tests in the server
folder. You'll need to cd
into the server
directory and run
pytest -x
to run the tests for the Flask backend until the first failure.
Make sure to try out your routes from the React frontend application as well
once you have everything set up. You can run your Flask server from the
server/
directory with:
$ python app.py
Or, if you have configured your Flask environment:
$ flask run
Start by generating a Message
model and the necessary migration code to create
messages with the following attributes:
- "body": String.
- "username": String.
- "created_at": String.
- "updated_at": DateTime.
After creating the model and migrations, run the migrations and use the provided
seed.py
file to seed the database:
$ flask db revision --autogenerate -m'your message'
$ flask db upgrade
$ python seed.py
Build out the following routes to handle the necessary CRUD actions:
GET /messages
: returns an array of all messages as JSON, ordered bycreated_at
in ascending order.POST /messages
: creates a new message with abody
andusername
from params, and returns the newly created post as JSON.PATCH /messages/<int:id>
: updates thebody
of the message using params, and returns the updated message as JSON.DELETE /messages/<int:id>
: deletes the message from the database.