How to separate Flask-Admin (auth example) into different files with imports

Question

I tried separating the codes from this sample Flask-Admin:
https://github.com/flask-admin/flask-admin/blob/master/examples/auth/app.py
However, it becomes messy as I add more codes so I tried to structure them but I'm getting some errors which I think is because of circular dependencies. I can run the homepage and the admin page, but I get some errors when I already tried to sign in (e.g. admin:admin).

__init__.py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

# create the Flask application
app = Flask(__name__)
app.config.from_pyfile('config.py')
db = SQLAlchemy(app)
headers = {'content-type': 'application/json'}

from myapp import app

app. py

import os
from flask import Flask, url_for, request, render_template, json, jsonify
from flask_security import Security, SQLAlchemyUserDatastore
from flask_security.utils import hash_password
import flask_admin, requests
from flask_admin import helpers as admin_helpers
from myapp import app, db, headers
from myapp.models import User, Role, MyModelView
from flask_script import Manager
from flask_migrate import Migrate, MigrateCommand


# Initialize flask-migrate and script manager
migrate = Migrate(app, db)
manager = Manager(app)

manager.add_command('db', MigrateCommand)

# Setup Flask-Security
user_datastore = SQLAlchemyUserDatastore(db.session, User, Role)
security = Security(app, user_datastore)

# Create admin
admin = flask_admin.Admin(
    app,
    'Administrator',
    base_template='my_master.html',
    template_mode='bootstrap3'
)

# Add model views
admin.add_view(MyModelView(Role, db.session))
admin.add_view(MyModelView(User, db.session))

# define a context processor for merging flask-admin's template context into the
# flask-security views.
@security.context_processor
def security_context_processor():
    return dict(
        admin_base_template=admin.base_template,
        admin_view=admin.index_view,
        h=admin_helpers,
        get_url=url_for
    )


def build_sample_db():
    """
    Populate a small db with some example entries.
    """

    import string
    import random

    db.drop_all()
    db.create_all()

    with app.app_context():
        user_role = Role(name='user')
        super_user_role = Role(name='superuser')
        db.session.add(user_role)
        db.session.add(super_user_role)
        db.session.commit()

        test_user = user_datastore.create_user(
            first_name='Admin',
            email='admin',
            password=hash_password('admin'),
            roles=[user_role, super_user_role]
        )

        first_names = [
            'Harry', 'Amelia', 'Oliver', 'Jack', 'Isabella', 'Charlie', 'Sophie', 'Mia',
            'Jacob', 'Thomas', 'Emily', 'Lily', 'Ava', 'Isla', 'Alfie', 'Olivia', 'Jessica',
            'Riley', 'William', 'James', 'Geoffrey', 'Lisa', 'Benjamin', 'Stacey', 'Lucy'
        ]
        last_names = [
            'Brown', 'Smith', 'Patel', 'Jones', 'Williams', 'Johnson', 'Taylor', 'Thomas',
            'Roberts', 'Khan', 'Lewis', 'Jackson', 'Clarke', 'James', 'Phillips', 'Wilson',
            'Ali', 'Mason', 'Mitchell', 'Rose', 'Davis', 'Davies', 'Rodriguez', 'Cox', 'Alexander'
        ]

        for i in range(len(first_names)):
            tmp_email = first_names[i].lower() + "." + last_names[i].lower() + "@example.com"
            tmp_pass = ''.join(random.choice(string.ascii_lowercase + string.digits) for i in range(10))
            user_datastore.create_user(
                first_name=first_names[i],
                last_name=last_names[i],
                email=tmp_email,
                password=hash_password(tmp_pass),
                roles=[user_role, ]
            )
        db.session.commit()
    return

# Flask views
@app.route('/')
def index():
    return render_template('index.html')

@app.route('/api/posts')
def getPosts():
    response = requests.get('...some_url', headers=headers)

    ...some codes here

if __name__ == '__main__':

    # Build a sample db on the fly, if one does not exist yet.
    app_dir = os.path.realpath(os.path.dirname(__file__))
    database_path = os.path.join(app_dir, app.config['DATABASE_FILE'])
    if not os.path.exists(database_path):
        build_sample_db()

    # Start app
    app.secret_key = 'secret_key'
    app.run(debug=True)

    # Start script manager
    manager.run()

models.py

from flask import abort, redirect, url_for, request
from flask_security import UserMixin, RoleMixin, login_required, current_user
from flask_admin.contrib import sqla
from myapp import db


# Define models
roles_users = db.Table(
    'roles_users',
    db.Column('user_id', db.Integer(), db.ForeignKey('user.id')),
    db.Column('role_id', db.Integer(), db.ForeignKey('role.id'))
)


class Role(db.Model, RoleMixin):
    id = db.Column(db.Integer(), primary_key=True)
    name = db.Column(db.String(80), unique=True)
    description = db.Column(db.String(255))

    def __str__(self):
        return self.name


class User(db.Model, UserMixin):
    id = db.Column(db.Integer, primary_key=True)
    first_name = db.Column(db.String(255))
    last_name = db.Column(db.String(255))
    email = db.Column(db.String(255), unique=True)
    password = db.Column(db.String(255))
    active = db.Column(db.Boolean())
    confirmed_at = db.Column(db.DateTime())
    roles = db.relationship('Role', secondary=roles_users,
                            backref=db.backref('users', lazy='dynamic'))

    def __str__(self):
        return self.email


# Create a user to test with
class MyModelView(sqla.ModelView):

    def is_accessible(self):
        if not current_user.is_active or not current_user.is_authenticated:
            return False

        if current_user.has_role('superuser'):
            return True

        return False

    def _handle_view(self, name, **kwargs):
        """
        Override builtin _handle_view in order to redirect users when a view is not accessible.
        """
        if not self.is_accessible():
            if current_user.is_authenticated:
                # permission denied
                abort(403)
            else:
                # login
                return redirect(url_for('security.login', next=request.url))

I also have a separate config file. And this is the error I get:

2017-09-12 14:32:37,285 INFO sqlalchemy.engine.base.Engine SELECT user.id AS user_id, user.first_name AS user_first_name, user.last_name AS user_last_name, user.email AS user_email, user.password AS user_password, user.active AS user_active, user.confirmed_at AS user_confirmed_at 
FROM user 
WHERE lower(user.email) = lower(%s) 
 LIMIT %s
2017-09-12 14:32:37,285 INFO sqlalchemy.engine.base.Engine ('admin', 1)
2017-09-12 14:32:37,312 INFO sqlalchemy.engine.base.Engine SELECT `role`.id AS role_id, `role`.name AS role_name, `role`.description AS role_description 
FROM `role`, roles_users 
WHERE %s = roles_users.user_id AND `role`.id = roles_users.role_id
2017-09-12 14:32:37,312 INFO sqlalchemy.engine.base.Engine (1L,)
[2017-09-12 14:32:37,314] ERROR in app: Exception on /admin/login/ [POST]
Traceback (most recent call last):
  File "/home/.../myapp/venv/local/lib/python2.7/site-packages/flask/app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/.../myapp/venv/local/lib/python2.7/site-packages/flask/app.py", line 1615, in full_dispatch_request
    return self.finalize_request(rv)
  File "/home/.../myapp/venv/local/lib/python2.7/site-packages/flask/app.py", line 1632, in finalize_request
    response = self.process_response(response)
  File "/home/.../myapp/venv/local/lib/python2.7/site-packages/flask/app.py", line 1856, in process_response
    response = handler(response)
  File "/home/.../myapp/venv/local/lib/python2.7/site-packages/flask_security/views.py", line 58, in _commit
    _datastore.commit()
  File "/home/.../myapp/venv/local/lib/python2.7/site-packages/flask_security/datastore.py", line 31, in commit
    self.db.session.commit()
AttributeError: 'scoped_session' object has no attribute 'session'
2017-09-12 14:32:37,314 INFO sqlalchemy.engine.base.Engine ROLLBACK
127.0.0.1 - - [12/Sep/2017 14:32:37] "POST /admin/login/ HTTP/1.1" 500 -

Answer 1

Okay, to avoid any circular dependency issues, move your extensions to an extensions.py file, like so:

from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()

from flask_script import Manager
from flask_migrate import Migrate, MigrateCommand
migrate = Migrate()
manager = Manager()

and then in app.py so that you bind your extensions after the creation of the instance (you could even do this after)

if __name__ == "__main__":

else,

from extensions import db, migrate, manager 

app = Flask(__name__)
db.init_app(app)
migrate.init_app(app, db)
manager.init_app(app)
manager.add_command('db', MigrateCommand)

& to better understand your error, you could read about the flask-sqlalchemy extension (here) and the difference between an sqlalchemy session, a flask session & how to make the two interact with scoped sessions(here)