Phase 4 Full-Stack Application Project Template

Learning Goals

• 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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Introduction

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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.py

A 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.

Where Do I Start?

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.

Removing Existing Git Configuration

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 .canvas

The 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.

Creating Your Own Git Repo

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 mv command in a terminal within VS Code, you should close VS Code then reopen it.

Note: mv actually 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.

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Setup

server/

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 shell

You can run your Flask API on localhost:5555 by running:

python server/app.py

Check that your server serves the default route http://localhost:5555. You should see a web page with the heading "Project Server".

client/

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 client

You can run your React app on localhost:3000 by running:

npm start --prefix client

Check that your the React client displays a default page http://localhost:3000. You should see a web page with the heading "Project Client".

Generating Your Database

NOTE: The initial project directory structure does not contain the instance or migrations folders. Change into the server directory:

cd server

Then 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.py

Edit 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.

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config.py

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 name

If 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

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!"

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Updating Your README.md

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.

What Goes into a README?

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.

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Conclusion

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!

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Resources

• Setting up a respository - Atlassian
• Create a repo- GitHub Docs
• Markdown Cheat Sheet
• Python Circular Imports - StackAbuse
• Flask-CORS