from flask_sqlalchemy import SQLAlchemy

from flask import Flask

app = Flask(__name__)

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////tmp/test.db'

db = SQLAlchemy(app)

follows=db.Table('follows',

                 db.Column('follower_id',db.Integer,db.ForeignKey('users.id')),

                 db.Column('followed_id',db.Integer,db.ForeignKey('users.id')))

class User(db.Model):

    __tablename__ = 'users'

    id = db.Column(db.Integer, primary_key=True)

    username = db.Column(db.String(64), unique=True, index=True)

    followers=db.relationship('User',

                              secondary=follows,

                              primaryjoin=id==follows.c.followed_id,

                              secondaryjoin=id==follows.c.follower_id,

                              backref=db.backref('followed',lazy='dynamic'),

                              lazy='dynamic')

u1,u2=User(username='u1'),User(username='u2')

u1.followed.append(u2)

print "u1 following :",u1.followed[0].username

print "u2 followers :",u2.followers[0].username