there's an old ticket proposing to add the feature of "changing the class" of an item but it has many tricky turns and corners and hasn't been worth the large amount of effort it would take to make it work perfectly in all cases. It is of course much easier to do with single-table inheritance, though.
Ideally your application would be creating User or Person objects as appropriate from the start. If that's not how your system works, and it's typical that Person objects become User objects later on, I'd use composition for that. On Oct 29, 2012, at 11:43 AM, Alex Chamberlain wrote: > So, there's no way to upgrade a Person to a User within the normal ORM? > > Thanks, > > Alex > > On Oct 29, 2012 3:00 PM, "Michael Bayer" <[email protected]> wrote: > > On Oct 29, 2012, at 5:06 AM, Alex Chamberlain wrote: > >> I posted this on StackOverflow (http://stackoverflow.com/q/13109085/961353), >> but it received no answers so I'm hoping I'll have more luck here. >> >> I'm developing a small database where there are far more People than Users, >> so currently have the following Model.(I'm using Flask-SQLAlchemy and db is >> an instance of flask.ext.sqlalchemy.SQLAlchemy.) >> >> class Person(db.Model): >> __tablename__ = 'people' >> id = db.Column(db.Integer, primary_key = True) >> forename = db.Column(db.String(64)) >> surname = db.Column(db.String(64)) >> >> memberships = db.relationship('Membership', backref='person') >> >> @property >> def name(self): >> return self.forename + ' ' + self.surname >> >> def __repr__(self): >> return '<Person %r %r>' % (self.forename, self.surname) >> >> class User(Person): >> __tablename__ = 'users' >> id = db.Column(db.Integer, db.ForeignKey('people.id'), >> primary_key = True) >> email = db.Column(db.String(120), index = True, unique = True) >> role = db.Column(db.SmallInteger, default = ROLE_USER) >> >> salt = db.Column(db.BINARY(8)) >> password = db.Column(db.BINARY(20)) >> >> def __repr__(self): >> return '<User %r>' % (self.email) >> >> It's working quite well, in that if I create a User then a Person also get's >> saved. The problem is creating a User when a Person already exists in the >> database. >> >> I have tried the following: >> >> >>> p = models.Person.query.get(3) >> >>> u = models.User(id=p.id, email="[email protected]") >> >>> u.set_password('password') >> >>> db.session.add(u) >> >>> db.session.commit() >> Traceback >> ... >> sqlalchemy.exc.IntegrityError: (IntegrityError) PRIMARY KEY must be >> unique u'INSERT INTO people (id, forename, surname) VALUES (?, ?, ?)' (3, >> None, None) > > You're using joined table inheritance here, so the creation of a new User > object means that a row for both "users" and "people" will be generated. > There's no such thing as a "User that points to a Person" in this model, > there's only Persons and Users (who are also Persons). > > Your two options are to use composition instead of inheritance here (i.e. a > one-to-one relationship) or to work around the model by manually inserting > rows into "user", that is, session.execute(User.__table__.insert(), {params}). > > > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
