Gain insights into developing web applications using Flask, a lightweight and easy-to-learn Python framework. Delve into techniques that make you a sought-after full-stack developer.

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This project-based course is a detailed guide to web application development using the increasingly popular Flask framework.

Flask is known for being simple, lightweight and having a small learning curve. If you've got some experience in Python, picking up Flask will be a breeze. It's got a booming job market and will put you on track to becoming an in-demand full-stack developer. What's not to love?

Flask: Develop Web Applications in Python

"""Flask Application for Paws Rescue Center."""
from flask import Flask, render_template, abort
from forms import SignUpForm, LoginForm
from flask import session, redirect, url_for
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SECRET_KEY'] = 'dfewfew123213rwdsgert34tgfd1234trgf'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///paws.db'
db = SQLAlchemy(app)

"""Model for Pets."""
class Pet(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String, unique=True)
    age = db.Column(db.String)
    bio = db.Column(db.String)
    posted_by =  db.Column(db.String, db.ForeignKey('user.id'))


"""Model for Users."""
class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    full_name = db.Column(db.String)
    email = db.Column(db.String, unique=True)
    password = db.Column(db.String)
    pets = db.relationship('Pet', backref = 'user')

db.create_all()

"""Information regarding the Pets in the System."""
pets = [
            {"id": 1, "name": "Nelly", "age": "5 weeks", "bio": "I am a tiny kitten rescued by the good people at Paws Rescue Center. I love squeaky toys and cuddles."},
            {"id": 2, "name": "Yuki", "age": "8 months", "bio": "I am a handsome gentle-cat. I like to dress up in bow ties."},
            {"id": 3, "name": "Basker", "age": "1 year", "bio": "I love barking. But, I love my friends more."},
            {"id": 4, "name": "Mr. Furrkins", "age": "5 years", "bio": "Probably napping."}, 
        ]

"""Information regarding the Users in the System."""
users = [
            {"id": 1, "full_name": "Pet Rescue Team", "email": "team@pawsrescue.co", "password": "adminpass"},
        ]

@app.route("/")
def homepage():
    """View function for Home Page."""
    return render_template("home.html", pets = pets)


@app.route("/about")
def about():
    """View function for About Page."""
    return render_template("about.html")


@app.route("/details/<int:pet_id>")
def pet_details(pet_id):
    """View function for Showing Details of Each Pet.""" 
    pet = next((pet for pet in pets if pet["id"] == pet_id), None) 
    if pet is None: 
        abort(404, description="No Pet was Found with the given ID")
    return render_template("details.html", pet = pet)


@app.route("/signup", methods=["POST", "GET"])
def signup():
    """View function for Showing Details of Each Pet.""" 
    form = SignUpForm()
    if form.validate_on_submit():
        new_user = {"id": len(users)+1, "full_name": form.full_name.data, "email": form.email.data, "password": form.password.data}
        users.append(new_user)
        return render_template("signup.html", message = "Successfully signed up")
    return render_template("signup.html", form = form)


@app.route("/login", methods=["POST", "GET"])
def login():
    form = LoginForm()
    if form.validate_on_submit():
        user = next((user for user in users if user["email"] == form.email.data and user["password"] == form.password.data), None)
        if user is None:
            return render_template("login.html", form = form, message = "Wrong Credentials. Please Try Again.")
        else:
            session['user'] = user
            return render_template("login.html", message = "Successfully Logged In!")
    return render_template("login.html", form = form)

@app.route("/logout")
def logout():
    if 'user' in session:
        session.pop('user')
    return redirect(url_for('homepage', _scheme='https', _external=True))
    
if __name__ == "__main__":
    app.run(debug=True, host="0.0.0.0", port=3000)


from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, SubmitField
from wtforms.validators import InputRequired, Email, EqualTo

class SignUpForm(FlaskForm):
    full_name = StringField('Full Name', validators = [InputRequired()])
    email = StringField('Email',
                        validators = [InputRequired(), Email()])
    password = PasswordField('Password', validators = [InputRequired()])
    confirm_password = PasswordField('Confirm Password',
                                     validators = [InputRequired(), EqualTo('password')])
    submit = SubmitField('Sign Up')

class LoginForm(FlaskForm):
    email = StringField('Email',
                        validators = [InputRequired(), Email()])
    password = PasswordField('Password', validators = [InputRequired()])
    submit = SubmitField('Login')

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# Explanation
In this challenge, we were tasked with creating a **one-to-many** relationship between the `Pet` and `User` models. This relationship should indicate that a **pet** can only be posted by one **user**. However, a **user** can post multiple **pets**. To solve this challenge, we used the following steps:
1. First, we created a `ForeignKey()` column in the model that only has **one** instance of the other model associated with it. In our case, this was the `Pet` model. So, we created this column in **line 18** and called it `posted_by`. It should contain the `user.id` as the `ForeignKey()`. 
2. Then, in the `User` model, we created a `relationship()` in **line 27**. We created this relationship with the `Pet` model and also created a `backref` with the name `user`. This back-reference will enable us to point to a row in `User` by using `pet.user`. 

And that's it. We just created a **one-to-many** relationship in our project!

In this lesson, we will look at how we created the one-to-many relationship described in the challenge. 

Before Getting Started

Introduction to Flask

First Flask Application

Build File/Directory Explorer in Flask

Static Templates

Static Files

Dynamic Templates

Form Handling

Database

Operations on Models

Conclusion

Test a MEAN Stack Todo Application with JEST

Build an E-Learning Website Using Flask

Solution: Create a One-to-Many Relationship