Question

The following totally incomplete snippet defines a basic SQLAlchemy relationship using declarative syntax…

Base = declarative_base()
class Movie(Base):
    __tablename__ = 'movies'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    director = relationship("People", uselist = False)

class People(Base):
    __tablename__ = 'people'
    id = Column(Integer, primary_key=True)
    name = Column(String, nullable = false)

To access the director name it would be something like:

assert isinstance(movie, Movie) # <-- retrieved with query or whatever
director_name = movie.director.name

If, for convenience, I always want the director relationship to just give me the director’s name, rather than a People instance, how do you do this? eg: it should work just like this:

assert isinstance(movie, Movie)
director_name = movie.director  # <-- should get the string directly

I’m 99% sure I’ve done this before but can’t find any reference code or documentation on it anymore. I’m going a bit crazy trying to locate it. Stack Overflow will be a good/permanent reference location for the answer.

Answer 1

The association proxy is used for all kinds of “object reference-> attribute reference” styles of transformation on the Python side. Docs have been newly updated and rewritten:

http://www.sqlalchemy.org/docs/orm/extensions/associationproxy.html