models.py

import click
from flask.cli import with_appcontext
from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

class Role(db.Model):
    __tablename__ = 'roles'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(64), unique=True)
    #atributo users devolverá a lista de usuários associados a essa função 'role'
    # db.relationship informa qual modelo está do outro lado
    #backref direção inversa do relacionamento, adiciona o ATRIBUTO 'role' ao modelo 'user'
    users = db.relationship('User', backref='role')

    def __repr__(self):
        return f'<Role {self.name!r}>'

class User(db.Model):
    __tablename__ = 'users'
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), unique=True, index=True)
    role_id = db.Column(db.Integer, db.ForeignKey('roles.id'))

    def __repr__(self):
        return f'<User {self.username!r}>'


def init_db():
    db.create_all()

@click.command('init-db')
@with_appcontext
def init_db_command():
    "Cria as tabelas do modelo"
    init_db()
    click.echo("Inicializando database")

def init_app(app):
    db.init_app(app)
    app.cli.add_command(init_db_command)