Creating a database in flask sqlalchemy

Question

I'm building a Flask app with Flask-SQLAlchemy and I'm trying to write a script that will create a Sqlite3 database without running the main application. In order to avoid circular references, I've initialized the main Flask app object and the SQLAlchemy database object in separate modules. I then import and combine them in a third file when running the app. This works fine when I'm running the app, as the database is built and operates properly when create rows and query them. However, when I try to import them in another module, I get the following error:

RuntimeError: application not registered on db instance and no applicationbound to current context

My code looks like the following:

root/create_database.py

from application.database import db
from application.server import app
db.init_app(app)
db.create_all()

root/run.sh

export FLASK_APP=application/server.py
flask run

root/application/init.py

from database import db
from server import app
db.init_app(app) 
from routes import apply_routes 
apply_routes(app)

root/application/database.py

from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()

root/application/server.py

from flask import Flask
import os
app = Flask(__name__)
path = os.path.dirname( os.path.realpath(__file__) )
database_path = os.path.join(path, '../mydb.sqlite')
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///' + database_path

root/application/models/init.py

from user import User

root/application/models/user.py

from application.database import db
class User(db.Model):
 id = db.Column(db.Integer, primary_key=True)
 username = db.Column(db.String(80), unique=True)
 password = db.Column(db.String(120))
 def __init__(self, username, password):
 self.username = username
 self.password = password

In my create_database.py script I'm trying to make sure that the SQLAlchemy db instance is configured with the config details from the app object, but it doesn't seem to be connecting for some reason. Am I missing something important here?

Answer 1

You either have to create a request or you have to create the models with sqlalchemy directly. We do something similar at work and chose the former.

Flask lets you create a test request to initialize an app. Try something like

from application.database import db
from application.server import app
with app.test_request_context():
 db.init_app(app)
 db.create_all()

• cardamom: Thanks, that was easy. What was also nice about the db.create_all() it is that it seems to be 'idempotent'. Not saying I know that it's that, but just experimented with that code and it creates the tables if they don't exist, but when it is run subsequent times, it just leaves them alone and rows are added to the existing.
• Cfreak: @cardamom yes it only creates them once. Though I believe it alters the tables if something has changed in the model. I know some developers run it every time their app initializes.