Thanks, that worked like a charm. Look forward to your PyCon
presentation.
On Feb 2, 12:56 am, Michael Bayer <mike...@zzzcomputing.com> wrote:
> On Feb 1, 2010, at 9:24 PM, Andy (Zenom) wrote:
>
>
>
>
>
> > I don't know if my terminology is correct etc. But the basic idea is
> > the following.
>
> > In my model I have something like
>
> > from mylib.helpers import slugify
>
> > class MyModel(Base):
> > __tablename__ = "testing"
>
> > id = Column(Integer, primary_key)
> > title = Column(Unicode)
> > description = Column(Unicode)
>
> > @property
> > def slug(self):
> > return slugify(self.title)
>
> > Now I want to be able to do something like.
> > session.query(MyModel.id, MyModel.title, MyModel.slug).all()
>
> > The table obviously doesn't have a slug column, I just want to return
> > my title as a "pseudo-column" named slug, with it passed through my
> > slugify method first.
>
> > I tried to do something like the following:
>
> > @synonym_for("title")
> > @property
> > def slug(self):
> > return slugify(self.title)
>
> > And this did not work. It seems to just return another column just
> > like title (not sent through slugify first). Any idea how I can do
> > what I am looking for?
>
> part of the approach depends on if "slugify" can be defined as a SQL function
> or if it must be executed in Python. If the latter, you probably want
> MyModel.slug to resolve into a column that also defines a custom type.
>
> Assuming its a Python function, note that your column can't be used
> effectively in a comparison operation, like "MyModel.slug == 'foo'", since
> the slugify() operation would have to be applied in aggregate.
>
> Anyway assuming non-SQL function, here's a hack I came up with that will do
> it:
>
> from sqlalchemy import *
> from sqlalchemy.orm import *
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.sql.expression import _UnaryExpression
> from sqlalchemy.types import UserDefinedType
>
> Base = declarative_base()
>
> def slugify(text):
> return "SLUG !" + text
>
> class MySlugType(UserDefinedType):
> def result_processor(self, dialect, coltype):
> return slugify
>
> class MyModel(Base):
> __tablename__ = "testing"
>
> id = Column(Integer, primary_key=True)
> title = Column(Unicode)
> description = Column(Unicode)
>
> slug = column_property(_UnaryExpression(title, type_=MySlugType()))
>
> engine = create_engine('sqlite://', echo=True)
> Base.metadata.create_all(engine)
> session = sessionmaker(engine)()
>
> session.add(MyModel(title=u'title', description=u'description'))
> session.commit()
>
> print session.query(MyModel.title, MyModel.slug).all()
>
>
>
>
>
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