python - Flask-sqlalchemy: sqlalchemy.exc.InvalidRequestError

Question

I'm building a backend for my iOS app and I choose to use Flask framework.

For the database part, I use flask-sqlalchemy to connect my mysql database.

When I put all my test code in a single file, everything works fine.

test.py

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = "mysql://root:pwd@localhost/test"
db = SQLAlchemy(app)


class player(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True)
    email = db.Column(db.String(120), unique=True)

    def __init__(self, username, email):
        self.username = username
        self.email = email

    def __repr__(self):
        return '<User %r>' % self.username

db.create_all()

However, when I split the code into different files in order to make the whole project structured, I got an error.

Here's my file structure:

.
├── config.py
├── app.py
├── app
    ├── __init__.py
    ├── api.py
    └── models.py
└── venv

config.py

SQLALCHEMY_DATABASE_URI = "mysql://root:pwd@localhost/test"

app.py

from app import app

if __name__ == '__main__':
    app.run(debug=True)

__init.py__

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

import config

app = Flask(__name__)
app.config.from_object("config")
db = SQLAlchemy(app)

import models
db.create_all()

models.py

from app import db

class player(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True)
    email = db.Column(db.String(120), unique=True)

    def __init__(self, username, email):
        self.username = username
        self.email = email

    def __repr__(self):
        return '<User %r>' % self.username

When I ran __init__.py to create all the tables in models.py, I got error

sqlalchemy.exc.InvalidRequestError: Table 'player' is already defined for this MetaData instance. Specify 'extend_existing=True' to redefine options and columns on an existing Table object.

And when I check the database, I found that table player is created.

It seems that sqlalchemy is trying to create the tables repeatedly.

Why is that?

Flask try create table on every run, such as you put db.create_all() into __init__.py You should put create db commands into separate script, try use Flask-Script and alembic (http://flask-script.readthedocs.io/en/latest/). Into test.py you can set db.drop_all() before db.create_all() — VelikiiNehochuha, May 05 '16 at 13:55
I have left db.create_all() in my app init file without any problems. What I see different in your script from my scripts is that player model. I always define my models with propercase so try changing 'player(db.Model)' to 'Player(db.Model)' — 8oh8, Dec 16 '16 at 22:44
The error tells you that a `Table` instance has been included in the `MetaData` already. That means that *you* are trying to create the `Table` instances repeatedly, but have not included enough code here to demonstrate how and where. Are you using reflection? Please produce a [mcve]. — Ilja Everilä, Feb 05 '18 at 07:38

score 0 · Answer 1 · edited May 23 '17 at 12:33

0

try

from app import models

instead of

import models

you are creating a circular import. See this link for more about circular imports

edited May 23 '17 at 12:33

Community

1
1

answered Feb 08 '17 at 01:38

betts

1

python - Flask-sqlalchemy: sqlalchemy.exc.InvalidRequestError

1 Answers1