(venv) $ pip install flask-sqlalchemy

from flask.ext.sqlalchemy import SQLAlchemy
basedir = os.path.abspath(os.path.dirname(__file__))
app = Flask(__name__)
app.config[‘SQLALCHEMY_DATABASE_URI‘] = ‘sqlite:///‘ + os.path.join(basedir, ‘data.sqlite‘)
app.config[‘SQLALCHEMY_COMMIT_ON_TEARDOWN‘] = True
db = SQLAlchemy(app)

class Role(db.Model):
 __tablename__ = ‘roles‘
 id = db.Column(db.Integer, primary_key=True)
 name = db.Column(db.String(64), unique=True)
 def __repr__(self):
 return ‘<Role %r>‘ % self.name

class User(db.Model):
 __tablename__ = ‘users‘
 id = db.Column(db.Integer, primary_key=True)
 username = db.Column(db.String(64), unique=True, index=True)
 def __repr__(self):
 return ‘<User %r>‘ % self.username

class Role(db.Model):
 # ...
 users = db.relationship(‘User‘, backref=‘role‘)
class User(db.Model):
 # ...
 role_id = db.Column(db.Integer, db.ForeignKey(‘roles.id‘))

(venv) $ python hello.py shell
>>> from hello import db
>>> db.create_all()

>>> from hello import Role, User
>>> admin_role = Role(name=‘Admin‘)
>>> mod_role = Role(name=‘Moderator‘)
>>> user_role = Role(name=‘User‘)
>>> user_john = User(username=‘john‘, role=admin_role)
>>> user_susan = User(username=‘susan‘, role=user_role)
>>> user_david = User(username=‘david‘, role=user_role)

>>> user = User.query.filter_by(username=‘john‘).first()

>>> db.session.delete(user)

>>> db.session.commit()

>>> admin_role.name = ‘Administrator‘
>>> db.session.add(admin_role)
>>> db.session.commit()

>>> Role.query.all()
[<Role u‘Administrator‘>, <Role u‘User‘>]
>>> User.query.all()
[<User u‘john‘>, <User u‘susan‘>, <User u‘david‘>]

>>> User.query.filter_by(role=user_role).all()
[<User u‘susan‘>, <User u‘david‘>]