Question

I’m following the Flask-SQLAlchemy tutorial. I have Flask 0.9, sqlalchemy 0.7.8 and flask-sqlalchemy 0.16 on python 2.6. (and I work with eclipse)

(The tuto is here : http://packages.python.org/Flask-SQLAlchemy/models.html)

I have 2 classes : a man and a wallet. There is a 1-1 relationship. (Each man has his own wallet)

class Man(db.Model):
    sid = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(100), unique=False)
    wallet = db.relationship('Wallet', backref='man', lazy='dynamic', uselist=False)

    def __init__(self, wallet):
        self.wallet = wallet

class Wallet(db.Model):
    sid = db.Column(db.Integer, primary_key=True)
    account = db.Column(db.Integer)
    manId = db.Column(db.Integer, db.ForeignKey('man.sid'))

    def __init__(self, account):
        self.account = account

In my “main” module, I create my database :

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:PATH'
db = SQLAlchemy(app)

In this very same module, I try to attach a Wallet to a Man :

if __name__ == "__main__":
    db.create_all() 
    w1 = Wallet(132)
    w2 = Wallet(18)
    db.session.add(w1)
    db.session.add(w2)
    db.session.commit()
    man1 = Man(w1)
    db.session.add(man1)
    db.session.commit()

But I get this error :

TypeError: 'Wallet' object is not iterable

I fail to understand why such an error appears. What is the right way of adding a mapped object ?

PS : I’ve been on the SQLAlchemy tutorial and I believe that they would declare things differently :

class Man(db.Model):
    sid = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(100), unique=False)
    wallet = db.relationship('Wallet', backref='man', lazy='dynamic', uselist=False)
    manId = db.Column(db.Integer, db.ForeignKey('man.sid'))
    def __init__(self, wallet):
        self.wallet = wallet

class Wallet(db.Model):
    sid = db.Column(db.Integer, primary_key=True)
    account = db.Column(db.Integer)

    def __init__(self, account):
        self.account = account

Which tutorial should I trust ?

Thank you very much !

Answer 1

I fail to understand why such an error appears. What is the right way of adding a mapped object ?

Notice that when you configure you wallet relationship you use lazy=”dynamic” option. This way you are setting up a dynamic relationship. As it is designed to be used with large collections it doesn’t really makes much sense to use it with one-to-one relationship.

At the same time it alters the way you can assign to your scalar relationship, i.e. you cannot assing your single object directly:

self.wallet = wallet

but you must use an iterable

self.wallet = [wallet]

So you have two solutions here: either assign collection of one element as shown above or better yet stop using dynamic collections for this relationship.