Here is the model used for many of the examples in this documentation. It is based on SQLAlchemy Declaratives. You may also recognize it from the TurboGears 2 quickstart template. It is similar, but with a few modifications.:

#most of this file was taken from turbogears default template
from hashlib import sha1
import os
import md5
import sha
from datetime import datetime

#from sqlalchemy.types import *
from sqlalchemy import *
from sqlalchemy.orm import relation, backref, synonym
from sqlalchemy.ext.declarative import DeclarativeMeta, declarative_base

DeclarativeBase = declarative_base()

metadata = DeclarativeBase.metadata

# This is the association table for the many-to-many relationship between
# groups and permissions.
group_permission_table = Table('tg_group_permission', metadata,
    Column('group_id', Integer, ForeignKey('tg_group.group_id',
        onupdate="CASCADE", ondelete="CASCADE")),
    Column('permission_id', Integer, ForeignKey('tg_permission.permission_id',
        onupdate="CASCADE", ondelete="CASCADE"))

# This is the association table for the many-to-many relationship between
# groups and members - this is, the memberships.
user_group_table = Table('tg_user_group', metadata,
    Column('user_id', Integer, ForeignKey('tg_user.user_id',
        onupdate="CASCADE", ondelete="CASCADE")),
    Column('group_id', Integer, ForeignKey('tg_group.group_id',
        onupdate="CASCADE", ondelete="CASCADE"))

# auth model

class Group(DeclarativeBase):
    """An ultra-simple group definition.
    __tablename__ = 'tg_group'

    group_id = Column(Integer, autoincrement=True, primary_key=True)
    group_name = Column(Unicode(16), unique=True)
    display_name = Column(Unicode(255))
    created = Column(DateTime, default=datetime.now)
    users = relation('User', secondary=user_group_table, backref='groups')

    def __repr__(self):
        return '<Group: name=%s>' % self.group_name

class Town(DeclarativeBase):
    __tablename__ = 'town'
    town_id = Column(Integer, primary_key=True)
    name = Column(String(32))

class User(DeclarativeBase):
    """Reasonably basic User definition. Probably would want additional
    __tablename__ = 'tg_user'

    user_id = Column(Integer, autoincrement=True, primary_key=True)
    user_name = Column(Unicode(16), unique=True)
    email_address = Column(Unicode(255), unique=True)
    display_name = Column(Unicode(255))
    _password = Column('password', Unicode(40))
    created = Column(DateTime, default=datetime.now)
    town_id = Column(Integer, ForeignKey('town.town_id'))
    town = relation(Town)

    def __repr__(self):
        return '<User: email="%s", display name="%s">' % (
                self.email_address, self.display_name)

    def permissions(self):
        perms = set()
        for g in self.groups:
            perms = perms | set(g.permissions)
        return perms

    def by_email_address(cls, email):
        """A class method that can be used to search users
        based on their email addresses since it is unique.
        return DBSession.query(cls).filter(cls.email_address==email).first()

    def by_user_name(cls, username):
        """A class method that permits to search users
        based on their user_name attribute.
        return DBSession.query(cls).filter(cls.user_name==username).first()

    def _set_password(self, password):
        """encrypts password on the fly using the encryption
        algo defined in the configuration
        #unfortunately, this causes coverage not to work
        #self._password = self._encrypt_password(algorithm, password)

    def _get_password(self):
        """returns password
        return self._password

    password = synonym('password', descriptor=property(_get_password,

    def _encrypt_password(self, algorithm, password):
        """Hash the given password with the specified algorithm. Valid values
        for algorithm are 'md5' and 'sha1'. All other algorithm values will
        be essentially a no-op."""
        hashed_password = password

        if isinstance(password, unicode):
            password_8bit = password.encode('UTF-8')
            password_8bit = password

        #creates a salted sha password
        salt = sha1()
        hash = sha1()
        hash.update(password_8bit + salt.hexdigest())
        hashed_password = salt.hexdigest() + hash.hexdigest()

        # make sure the hased password is an UTF-8 object at the end of the
        # process because SQLAlchemy _wants_ a unicode object for Unicode columns
        if not isinstance(hashed_password, unicode):
            hashed_password = hashed_password.decode('UTF-8')

        return hashed_password

    def validate_password(self, password):
        """Check the password against existing credentials.
        this method _MUST_ return a boolean.

        @param password: the password that was provided by the user to
        try and authenticate. This is the clear text version that we will
        need to match against the (possibly) encrypted one in the database.
        @type password: unicode object
        hashed_pass = sha1()
        hashed_pass.update(password + self.password[:40])

        return self.password[40:] == hashed_pass.hexdigest()

class Permission(DeclarativeBase):
    """A relationship that determines what each Group can do
    __tablename__ = 'tg_permission'

    permission_id = Column(Integer, autoincrement=True, primary_key=True)
    permission_name = Column(Unicode(16), unique=True)
    description = Column(Unicode(255))
    groups = relation(Group, secondary=group_permission_table,

class Example(DeclarativeBase):
    __tablename__  = 'example_table'

    example_id      = Column(Integer, primary_key=True)
    created         = Column(DateTime, default=datetime.now)
    blob            = Column(BLOB          )
    binary          = Column(Binary        )
    boolean         = Column(Boolean       )
    char            = Column(CHAR(200)     )
    cLOB            = Column(CLOB(200)     )
    date_           = Column( DATE         )
    datetime_       = Column( DATETIME     )
    decimal         = Column(DECIMAL       )
    date            = Column(Date          )
    dateTime        = Column(DateTime      )
    float__         = Column( FLOAT        )
    float_          = Column(Float         )
    int_            = Column(INT           )
    integer         = Column(Integer, default=10)
   # (NCHAR =       #Column NCHAR          )
    numeric         = Column(Numeric       )
    pickletype      = Column(PickleType    )
    smallint        = Column(SMALLINT      )
    smalliunteger   = Column(SmallInteger  )
    string          = Column(String(20)    )
    text            = Column(TEXT(20)      )
    time_           = Column(TIME          )
    time            = Column(Time          )
    timestamp       = Column(TIMESTAMP     )
    unicode_        = Column(Unicode(200)  )
    varchar         = Column(VARCHAR(200)  )
    password        = Column(String(20)    )


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