I'm new to SqlAlchemy and Elixir, so I've started from tutorial and tried to create table, insert a record, and then update it as follows:

#'elixir_test.py'
from elixir import *

metadata.bind = "postgresql://myuser:mypwd@localhost:5432/dbname"
metadata.bind.echo = True

class Movie(Entity):
    title = Field(Unicode(30))
    year = Field(Integer)
    description = Field(UnicodeText)

    def __repr__(self):
        return '<Movie "%s" (%d)>' % (self.title, self.year)

and in another file in the same directory:

from elixir_test import *

setup_all()
#create table
create_all()

Movie(title=u"Blade Runner", year=1982)

#add record
session.commit()

#get records
Movie.query.all()

#trying to update record and commit changes, BUT...
movie = Movie.query.first()
movie.year = 1983
session.commit()

#now we have two records in our table, one 
#with year=1982 and one with year=1983
Movie.query.all()

What did I missed?