- Discuss the basic directory structure of a full-stack Flask/React application.
- Carry out the first steps in creating your Phase 4 project.
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Fork and clone this lesson for a template for your full-stack application. Take a look at the directory structure before we begin (NOTE: node_modules will be generated in a subsequent step):
$ tree -L 2
$ # the -L argument limits the depth at which we look into the directory structure
.
├── CONTRIBUTING.md
├── LICENSE.md
├── Pipfile
├── README.md
├── client
│ ├── README.md
│ ├── package.json
│ ├── public
│ └── src
└── server
├── app.py
├── config.py
├── models.py
└── seed.pyA migrations folder will be added to the server directory in a later step.
The client folder contains a basic React application, while the server
folder contains a basic Flask application. You will adapt both folders to
implement the code for your project .
NOTE: If you did not previously install tree in your environment setup, MacOS
users can install this with the command brew install tree. WSL and Linux users
can run sudo apt-get install tree to download it as well.
Just as with your Phase 3 Project, this will likely be one of the biggest projects you've undertaken so far. Your first task should be creating a Git repository to keep track of your work and roll back any undesired changes.
If you're using this template, start off by removing the existing metadata for Github and Canvas. Run the following command to carry this out:
$ rm -rf .git .canvasThe rm command removes files from your computer's memory. The -r flag tells
the console to remove recursively, which allows the command to remove
directories and the files within them. -f removes them permanently.
.git contains this directory's configuration to track changes and push to
Github (you want to track and push your own changes instead), and .canvas
contains the metadata to create a Canvas page from your Git repo. You don't have
the permissions to edit our Canvas course, so it's not worth keeping around.
First things first- rename this directory! Once you have an idea for a name,
move one level up with cd .. and run
mv python-p4-project-template <new-directory-name> to change its name (replace
with an appropriate project directory name).
Note: If you typed the
mvcommand in a terminal within VS Code, you should close VS Code then reopen it.
Note:
mvactually stands for "move", but your computer interprets this rename as a move from a directory with the old name to a directory with a new name.
cd back into your new directory and run git init to create a local git
repository. Add all of your local files to version control with git add --all,
then commit them with git commit -m'initial commit'. (You can change the
message here- this one is just a common choice.)
Navigate to GitHub. In the upper-right corner of the page, click on the "+" dropdown menu, then select "New repository". Enter the name of your local repo, choose whether you would like it to be public or private, make sure "Initialize this repository with a README" is unchecked (you already have one), then click "Create repository".
Head back to the command line and enter
git remote add origin git@github.com:github-username/new-repository-name.git.
NOTE: Replace github-username with your github username, and
new-repository-name with the name of your new repository. This command will
map the remote repository to your local repository. Finally, push your first
commit with git push -u origin main.
Your project is now version-controlled locally and online. This will allow you to create different versions of your project and pick up your work on a different machine if the need arises.
The server/ directory contains all of your backend code.
app.py is your Flask application. You'll want to use Flask to build a simple
API backend like we have in previous modules. You should use Flask-RESTful for
your routes. You should be familiar with models.py and seed.py by now, but
remember that you will need to use Flask-SQLAlchemy, Flask-Migrate, and
SQLAlchemy-Serializer instead of SQLAlchemy and Alembic in your models.
The project contains a default Pipfile with some basic dependencies. You may
adapt the Pipfile if there are additional dependencies you want to add for
your project.
To download the dependencies for the backend server, run:
pipenv install
pipenv shellYou can run your Flask API on localhost:5555 by
running:
python server/app.pyCheck that your server serves the default route http://localhost:5555. You
should see a web page with the heading "Project Server".
The client/ directory contains all of your frontend code. The file
package.json has been configured with common React application dependencies,
include react-router-dom. The file also sets the proxy field to forward
requests to `"http://localhost:5555". Feel free to change this to another port-
just remember to configure your Flask app to use another port as well!
To download the dependencies for the frontend client, run:
npm install --prefix clientYou can run your React app on localhost:3000 by
running:
npm start --prefix clientCheck that your the React client displays a default page
http://localhost:3000. You should see a web page with the heading "Project
Client".
NOTE: The initial project directory structure does not contain the instance or
migrations folders. Change into the server directory:
cd serverThen enter the commands to create the instance and migrations folders and
the database app.db file:
flask db init
flask db upgrade head
Type tree -L 2 within the server folder to confirm the new directory
structure:
.
├── app.py
├── config.py
├── instance
│ └── app.db
├── migrations
│ ├── README
│ ├── __pycache__
│ ├── alembic.ini
│ ├── env.py
│ ├── script.py.mako
│ └── versions
├── models.py
└── seed.pyEdit models.py and start creating your models. Import your models as needed in
other modules, i.e. from models import ....
Remember to regularly run
flask db revision --autogenerate -m'<descriptive message>', replacing
<descriptive message> with an appropriate message, and flask db upgrade head
to track your modifications to the database and create checkpoints in case you
ever need to roll those modifications back.
Tip: It's always a good idea to start with an empty revision! This allows you to roll all the way back while still holding onto your database. You can create this empty revision with
flask db revision -m'Create DB'.
If you want to seed your database, now would be a great time to write out your
seed.py script and run it to generate some test data. Faker has been included
in the Pipfile if you'd like to use that library.
When developing a large Python application, you might run into a common issue:
circular imports. A circular import occurs when two modules import from one
another, such as app.py and models.py. When you create a circular import and
attempt to run your app, you'll see the following error:
ImportError: cannot import nameIf you're going to need an object in multiple modules like app or db,
creating a third module to instantiate these objects can save you a great deal
of circular grief. Here's a good start to a Flask config file (you may need more
if you intend to include features like authentication and passwords):
# Standard library imports
# Remote library imports
from flask import Flask
from flask_cors import CORS
from flask_migrate import Migrate
from flask_restful import Api
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import MetaData
# Local imports
# Instantiate app, set attributes
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///app.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.json.compact = False
# Define metadata, instantiate db
metadata = MetaData(naming_convention={
"fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
})
db = SQLAlchemy(metadata=metadata)
migrate = Migrate(app, db)
db.init_app(app)
# Instantiate REST API
api = Api(app)
# Instantiate CORS
CORS(app)Now let's review that last line...
CORS (Cross-Origin Resource Sharing) is a system that uses HTTP headers to determine whether resources from different servers-of-origin can be accessed. If you're using the fetch API to connect your frontend to your Flask backend, you need to configure CORS on your Flask application instance. Lucky for us, that only takes one line:
CORS(app)By default, Flask-CORS enables CORS on all routes in your application with all
fetching servers. You can also specify the resources that allow CORS. The
following specifies that routes beginning with api/ allow CORS from any
originating server:
CORS(app, resources={r"/api/*": {"origins": "*"}})You can also set this up resource-by-resource by importing and using the
@cross_origin decorator:
@app.route("/")
@cross_origin()
def howdy():
return "Howdy partner!"README.md is a Markdown file that describes your project. These files can be
used in many different ways- you may have noticed that we use them to generate
entire Canvas lessons- but they're most commonly used as homepages for online
Git repositories. When you develop something that you want other people to
use, you need to have a README.
Markdown is not a language that we cover in Flatiron's Software Engineering curriculum, but it's not a particularly difficult language to learn (if you've ever left a comment on Reddit, you might already know the basics). Refer to the cheat sheet in this lesson's resources for a basic guide to Markdown.
This README should serve as a template for your own- go through the important files in your project and describe what they do. Each file that you edit (you can ignore your migration files) should get at least a paragraph. Each function should get a small blurb.
You should descibe your application first, and with a good level of detail. The rest should be ordered by importance to the user. (Probably routes next, then models.)
Screenshots and links to resources that you used throughout are also useful to users and collaborators, but a little more syntactically complicated. Only add these in if you're feeling comfortable with Markdown.
A lot of work goes into a full-stack application, but it all relies on concepts that you've practiced thoroughly throughout this phase. Hopefully this template and guide will get you off to a good start with your Phase 4 Project.
Happy coding!