Thanks Simon, I've tried the following: session.query(Employee).options(sa.orm.joinedload(Employee.jobs).load_only( 'id', 'first_name')).all()
which according to the documentation ( http://docs.sqlalchemy.org/en/rel_0_9/orm/mapper_config.html#deferred-loading-with-multiple-entities) should work, but it throws an exception (ArgumentError: mapper option expects string key or list of attributes) Can you please provide an example? Please notice that I'm trying to load only some properties of Employee (including one relationship) while this behavior should not be the default behavior (meaning that I don't want the defer the columns at model level) On Thursday, September 4, 2014 5:59:21 PM UTC+3, Simon King wrote: > > On Thu, Sep 4, 2014 at 3:28 PM, Ofir Herzas <[email protected] > <javascript:>> wrote: > > Hi, > > I have a model similar to the following: > > > > class Employee(Base): > > __tablename__ = "t_employee" > > > > id = sa.Column(Identifier, sa.Sequence('%s_id_seq' % __tablename__), > > primary_key=True, nullable=False) > > first_name = sa.Column(sa.String(30)) > > last_name = sa.Column(sa.String(30)) > > phone_number = sa.Column(sa.String(30)) > > > > _jobs = sa.orm.relationship("EmployeeJob", lazy="joined", > cascade="all, > > delete, delete-orphan") > > > > @property > > def name(self): > > return self.first_name + (" " + self.last_name if > len(self.last_name > > or "") > 0 else "") > > > > @property > > def jobs(self): > > return [item.job_id for item in sorted(self._jobs, > > key=attrgetter('id'))] > > > > @jobs.setter > > def jobs(self, value): > > self._jobs = [EmployeeJob(job_id=id_) for id_ in to_list(value)] > > > > class EmployeeJob(Base): > > id = sa.Column(sa.BigInteger, sa.Sequence('%s_id_seq' % > __tablename__), > > primary_key=True, nullable=False) > > employee_id = sa.Column(sa.BigInteger, sa.ForeignKey('t_employee.id', > > > ondelete="CASCADE"), nullable=False) > > job_id = sa.Column(sa.BigInteger, sa.ForeignKey('t_job.id', > > ondelete="CASCADE"), nullable=False) > > > > > > Now, I'm trying to write a simple query that will fetch all employees > with > > their jobs. > > As I understand, I need to use joinedload so that the list of jobs will > be > > eagerly loaded but I can't understand how to do it. > > > > I tried the following: > > session.query(Employee.id).options(sa.orm.joinedload(Employee.jobs)) > > > > but it doesn't work. > > > > Just to clarify, I want to load some of the columns, not all of them, > and > > I'm expecting to get the list of jobs for each employee (hopefully like > the > > getter produces them) > > > > session.query(Employee) does fetch the required information but it > selects > > some unneeded columns > > > > Also, how do I select the name property? > > > > Thanks, > > Ofir > > > > Eager loading means that when you have an instance of Employee, and > you access its 'jobs' property, no SQL is emitted because the data is > already available. This implies that you have to query for the > Employee class, not just one of its columns (otherwise you wouldn't > have an instance from which to access the "jobs" property) > > If you don't want to load all the Employee columns, you can defer them: > > > http://docs.sqlalchemy.org/en/rel_0_9/orm/mapper_config.html#deferred-column-loading > > > Hope that helps, > > Simon > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
