Operational error when I tried to create new tables - flask

Question

So, before adding a few columns I had username, password and email and it was working fine. But when I tried to add a few more things such as age, gender, phone and address I got this error:
sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) no such table: user [SQL: 'SELECT user.id AS user_id, user.username AS user_username, user.email AS user_email, user.password AS user_password, user.age AS user_age, user.gender AS user_gender, user.phone AS user_phone, user.address AS user_address \nFROM user \nWHERE user.username = ?\n LIMIT ? OFFSET ?'] [parameters: ('agam-kashyap', 1, 0)] (Background on this error at: http://sqlalche.me/e/e3q8)
The error seems to be in these lines:
#app.route("/register",methods = ['GET','POST'])
def register():
form = RegistrationForm()
if form.validate_on_submit():
user = User(username=form.username.data, email = form.email.data, password = form.password.data, age = form.age.data, gender = form.gender.data, phone = form.phone.data, address = form.address.data)
db.create_all()
db.session.add(user)
db.session.commit()
return redirect(url_for('login'))
return render_template('register.html', title= 'Register' , form = form)
Also, here is my User class:
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(20), unique=True, nullable=False)
email = db.Column(db.String(120), unique=True, nullable=False)
password = db.Column(db.String(60), nullable=False)
age = db.Column(db.String(3), nullable=False)
gender = db.Column(db.String(6), nullable=False)
phone = db.Column(db.String(10), nullable=False)
address = db.Column(db.String(200), nullable=False)
How can I solve this issue?

Answer 1

In keeping with Dave W. Smith's suggestion, the error is probably due to the fact that you did not perform any database migration operations for the new changes to take effect.
When a database model changes, as it does for you, the database must of course be updated. This is what you want to accomplish visibly.
So, you should note that the particularity with SQLAlchemy is that it creates tables from models only when they already exists.
It means that if you want to add new things to the database, modify or delete fields from your model, you have to destroy the old tables and recreate everything from scratch.
So the solution to work around this problem is to go through a database migration framework. Like a source code version control tool, a database migration framework tracks any changes that occur on the database schema. So it can apply incremental changes to the database.
For SQLAlchemy, there is an excellent database migration tool, I named: Alembic. But since you use Flask, you do not have to manipulate Alembic directly; There is a Flask extension that handles SQLAlchemy database migrations for Flask applications using Alembic: flask-migrate
As you are still a beginner with Flask, I recommend this excellent Miguel Grinberg's tutorial: the flask mega tutorial - part-iv :database. It will teach you the basics needed to work with Flask SQLAlchemy