How to add column to existing Table? in Flask SqlAlchemy

Question

I have a flask SqlAclchemy table called User:

class User(db.Model):
    id = db.Column(db.INTEGER, primary_key=True)
    username = db.Column(db.String(64), index=True, unique=True)

i have now edited it and added this line;favCol = db.Column(db.String(12))

how do i update the table for it to recognize this new colum when i add a new user? At the moment when i create a User like User(username="bob",favCol="red") it gives me an error:

TypeError: 'favCol' is an invalid keyword argument for User

I have heard of solution with Migrate although i would prefer re a simpler solution if possible

Yea, i did not find anything. I also tried : db.update(User) in the python console — Conor Jalen
– Conor Jalen, Commented Mar 21, 2021 at 20:54
You wouldn't get the invalid keyword argument for ... error if you've added the favCol = db.Column(...) declaration to your model correctly. You should expect to get a sqlalchemy.exc.OperationalError error when sqlalchemy tries to write to the table and the column doesn't exist yet in the database. — SuperShoot
– SuperShoot, Commented Mar 21, 2021 at 20:59
You're unlikely to get answers with any better info than these: stackoverflow.com/questions/7300948/… — SuperShoot
– SuperShoot, Commented Mar 21, 2021 at 21:03
Can i go to slite in the console and do something like : ALTER... — Conor Jalen
– Conor Jalen, Commented Mar 23, 2021 at 1:56

Andrew Clark · Accepted Answer · 2021-03-23 21:07:58Z

1

If you don't care about the data in the database getting erased. You can do the following:

from terminal if 'py' doesn't start python, try 'python'. press enter after each of these commands

py
from projectdirectory import db
db.drop_all()
db.create_all()

If you care about your existing data, you need to use something like flask_migrate which uses alembic in order to help you do database migrations while maintaining your data.

answered Mar 23, 2021 at 21:07

Andrew Clark

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2 Comments

Conor Jalen Over a year ago

Is there any solution without having my data erased?

Andrew Clark Over a year ago

Yes. refer to the last paragraph of my submitted answer. It's not a simple solution though. It's too complex to explain in a few lines here on how you could implement it. You'll have to research flask_migrate for yourself.

DarkGoldBar · Accepted Answer · 2022-06-08 06:55:29Z

0

This answer will help:
https://stackoverflow.com/a/17243132/19280304

For flask-SQLAlchemy, add this before the code

from flask_sqlalchemy import SQLAlchemy
engine  = SQLAlchemy(app).engine

answered Jun 8, 2022 at 6:55

DarkGoldBar

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