Flask error or 404 query resulting in SQL error

I'm trying to clean up some of my Flask code. I have this line which works:

user = User.query.filter_by(username=username).first()

But my preference is to use this so I can throw a 404. However whilst the above code works, this gives me an error:

user = User.query.get_or_404(username=username)

TypeError: get_or_404() got an unexpected keyword argument 'username'. If I try this:

user = User.query.get_or_404(username)

I also get an error:

> [SQL: SELECT "user".id AS user_id, "user".username AS user_username,
> "user".email AS user_email, "user".password_hash AS
> user_password_hash, "user".about_me AS user_about_me, "user".last_seen
> AS user_last_seen, "user".is_confirmed AS user_is_confirmed,
> "user".confirmed_on AS user_confirmed_on FROM "user" WHERE "user".id =
> %(pk_1)s] [parameters: {'pk_1': 'john'}]

How should I be using this query? It seems the error is trying to put the name as the ID which is obviously expecting a number.

In flask-sqlalchemy, like get(pk), get_or_404(param) also expects the primary key of the model inside the parameter. In your case, your username is not the primary key of the User model.

Instead, you can use user = User.query.filter_by(username=username).first_or_404() to get 404 if user not exists.