gistfile1.py

"""
example of (bug?) in adding deferred columns to a declarative class
after the
class's creation.

Foo is a normal declarative class with a deferred column. Bar is the
same class,
but with the deferred column added afterwards.
"""

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

metadata = MetaData('sqlite://')
metadata.bind.echo = True
Base = declarative_base(metadata=metadata)

class Foo(Base):
   __tablename__ = 'foos'
   id = Column(Integer(unsigned=True), primary_key=True)
   text = Column(String(20))
   deferme = deferred(Column(String(30)))

   def __init__(self, text, deferme):
       self.text = text
       self.deferme = deferme

   def __repr__(self):
       return "<Foo: id %d, text %s>" % (self.id, self.text)

class Bar(Base):
   __tablename__ = 'bars'
   id = Column(Integer(unsigned=True), primary_key=True)
   text = Column(String(20))

   def __init__(self, text, deferme):
       self.text = text
       self.deferme = deferme

   def __repr__(self):
       return "<Bar: id %d, text %s>" % (self.id, self.text)

Bar.deferme = deferred(Column('deferme', String(30)))

# This doesn't work either:
# Bar.deferme = deferred(Column(String(30)))

# populate
metadata.create_all()
sess = create_session()

foo1 = Foo('sqlalchemy', 'rocks')
foo2 = Foo('but', 'I')

bar1 = Bar('want', 'better')
bar2 = Bar('deferred', 'columns')

sess.add(foo1)
sess.add(foo2)

sess.add(bar1)
sess.add(bar2)

sess.flush()
sess.clear()

# query objects, get their addresses
print "all foos"
for f in sess.query(Foo).all():
   print f.text, f.deferme

print "all bars"
for b in sess.query(Bar).all():
   print b.text, b.deferme