Standalone Usage of web2py's DAL, gluon

"""
An example to use only gluon, which is the name of
web2py's data abstraction layer.
http://caglartoklu.blogspot.com/2011/06/standalone-usage-of-web2pys-dal-gluon.html
"""

import os
import sys

# web2py is distributed and deployed with zero configuration.
# Let us follow the same approach.
# To do this, I have opened a directory called "alone" inside
# the web2py directory, next to applications.

# I want to distribute the whole web2py directory.
# So, I want to make sure that the gluon is automatically found.

sys.path.append("../")
# print sys.path

from gluon.sql import DAL, Field
from gluon.validators import *

# For simplicity, we will be using SQLite.
# First, determine the path for the database file.
# We are headed for portability, so let us open the database
# file in the same directory with this module.

module_path = os.path.abspath(os.path.dirname(__file__))
# print module_path # => /home/alex/Projects/web2py/alone

# This is only the file name:
db_name = "our_db.sqlite"

# The protocol and full path to our database file.
db = DAL('sqlite://' + db_name, folder=module_path)

# Define the table "genre", note that the field "id" is automatic.
db.define_table("genre",
        Field("name"))
db.genre.name.requires = IS_NOT_EMPTY()

# Define the table "band", note that the field "id" is automatic.
# band.genre_id references to genre.id field.
db.define_table("band",
        Field("name"),
        Field("origin"),
        Field("genre_id", db.genre))
db.band.name.requires = IS_NOT_EMPTY()
db.band.genre_id.requires = IS_IN_DB(db, db.genre.id, '%(name)s')
db.band.genre_id.writable = False
db.band.genre_id.readable = False

# Let us insert some data for table "genre".
# Each insert statement returns the unique_id.
id_rock = db.genre.insert(name="rock")
id_metal = db.genre.insert(name="metal")
id_grunge = db.genre.insert(name="grunge")  # we will use the ID.
id_jazz = db.genre.insert(name="jazz")

# The data will be stored only after a commit.
db.commit()

# We can also do a rollback, before a commit.
print db.genre.insert(name="banana")
# It will print 5 to the screen.
db.rollback()
# But it will not be stored in the database.

# Let us insert some data for table "band".
db.band.insert(name="Nirvana", origin="Aberdeen", genre_id=id_grunge)
# Do not forget to commit.
db.commit()

# A simple select.
for row in db(db.band.name == 'Nirvana').select():
    print row.name, row.origin
    #prints Nirvana Aberdeen

# We can also take the last query.
print db._lastsql
# It will print this:
# SELECT  band.id, band.name, band.origin, band.genre_id FROM band
# WHERE (band.name = 'Nirvana');

# We can use free, raw SQL queries too.
print db.executesql('SELECT * FROM genre;')
# [(1, u'rock'), (2, u'metal'), (3, u'grunge'), (4, u'jazz')]