sqlalchemy ejemplo de tutorial que no funciona

Question

Estoy tratando de abrirme camino a través del ejemplo dado en el sqlalchemy tutorial pero estoy obteniendo errores. Por lo que puedo decir, estoy siguiendo el ejemplo a la letra. Aquí está el código que tengo de él hasta ahora. Falló cuando yo .first() después de consultar la base de datos.

estoy en la versión 0.7.5 y Python 2,7

from sqlalchemy     import Column, Integer, String 
from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy     import create_engine 
from sqlalchemy.orm    import sessionmaker 

engine = create_engine('sqlite:///:memory:', echo=True) 
engine.execute("select 1").scalar() # works fine 

Session = sessionmaker(bind=engine) 
session = Session() 
Base = declarative_base() 

class User(Base): 
    __tablename__ = 'users' 

    id = Column(Integer, primary_key=True) 
    name = Column(String) 
    fullname = Column(String) 
    password = Column(String) 

    def __init__(self, name, fullname, password): 
     self.name = name 
     self.fullname = fullname 
     self.password = password 

    def __repr__(self): 
     return "<User('%s','%s', '%s')>" % (self.name, self.fullname, self.password) 

jeff_user = User("jeff", "Jeff", "foo") 
session.add(jeff_user) 

our_user = session.query(User).filter_by(name='jeff').first() # fails here 

jeff_user.password = "foobar" 

session.add_all([ 
       User('wendy', 'Wendy Williams', 'foobar'), 
       User('mary', 'Mary Contrary', 'xxg527'), 
       User('fred', 'Fred Flinstone', 'blah')]) 

session.dirty # shows nothing as dirty 
session.new # shows nothing as new 

Aquí está el mensaje de error

2012-02-25 17:48:33,879 INFO sqlalchemy.engine.base.Engine BEGIN (implicit) 
2012-02-25 17:48:33,886 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, password) VALUES (?, ?, ?) 
2012-02-25 17:48:33,886 INFO sqlalchemy.engine.base.Engine ('jeff', 'Jeff', 'foo') 
2012-02-25 17:48:33,887 INFO sqlalchemy.engine.base.Engine ROLLBACK 
Traceback (most recent call last): 
    File "learning_sql.py", line 35, in <module> 
    our_user = session.query(User).filter_by(name='ed').first() # fails here 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line 2024, in first 
    ret = list(self[0:1]) 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line 1918, in __getitem__ 
    return list(res) 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line 2092, in __iter__ 
    self.session._autoflush() 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 983, in _autoflush 
    self.flush() 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1559, in flush 
    self._flush(objects) 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1630, in _flush 
    flush_context.execute() 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 331, in execute 
    rec.execute(self) 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 475, in execute 
    uow 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/mapper.py", line 2291, in _save_obj 
    execute(statement, params) 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1405, in execute 
    params) 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1538, in _execute_clauseelement 
    compiled_sql, distilled_params 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1646, in _execute_context 
    context) 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1639, in _execute_context 
    context) 
    File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 330, in do_execute 
    cursor.execute(statement, parameters) 
sqlalchemy.exc.OperationalError: (OperationalError) no such table: users u'INSERT INTO users (name, fullname, password) VALUES (?, ?, ?)' ('jeff', 'Jeff', 'foo') 

La impresión esperada a cabo este es

>>> our_user = session.query(User).filter_by(name='ed').first() 
BEGIN (implicit) 
INSERT INTO users (name, fullname, password) VALUES (?, ?, ?) 
('ed', 'Ed Jones', 'edspassword') 
SELECT users.id AS users_id, users.name AS users_name, users.fullname AS users_fullname, users.password AS users_password 
FROM users 
WHERE users.name = ? 
LIMIT 1 OFFSET 0 
('ed',) 
>>> our_user 
<User('ed','Ed Jones', 'edspassword')> 

Por alguna razón mi código está causando un ROLLBACK cuando debería ser SELECCIONADO.

Answer 1

Obtiene este error porque a la base de datos le falta la estructura de la tabla (aparentemente omitió esta línea en el tutorial, está en la subsección Declare Mapping). Crear el esquema añadiendo siguiente justo después de su mesa/definiciones de modelos:

Class User(Base) 
    ... 

# Initialize database schema (create tables) 
Base.metadata.create_all(engine)