Simple Model with Elixir

Table of Contents

• Simple Model with Elixir
  • How does the Model work?
  • Say Hello to the Model

Since we’re in a database-driven world, in practice the model will be based on a relational database. SQLAlchemy/SQLObject makes working with databases easy.

Elixir is a a declarative layer on top of SQLAlchemy. It remains the simplicity like SQLObject and the flexibility of SQLAlchemy.

For a real web application the very first thing you should customize is the location of the database your TurboGears app will use.

How does the Model work?

• setup a dburi
• setup an engine
• connect engine with an session
• manipulate the database
• flush the change back to the database.

Say Hello to the Model

Open dev.cfg and find the appropriate commented line for the SQL implementation you will be using. For this tutorial I will use SQLite because it uses a local file instead of a server connection:

sqlalchemy.dburi = "sqlite:///home/username/tutorial/tutorial.sqlite"

Note

If you choose SQLite, the URI must be an absolute path. And of course, you’ll need SQLite installed.

Note

The alternative is:

sqlalchemy.dburi = "sqlite://%(current_dir_uri)s/devdata.sqlite"

%(current_dir_uri)s is a TurboGears config shortcut for current path.

To define your database tables, open the existing file tutorial/model.py. TurboGears uses Elixir over SQLalchemy for database abstraction. In Elixir, classes represent tables and class attributes represent columns. Since I’m making a to-do list application, I added the following classes in tutorial/model.py:

from sqlalchemy import *
from turbogears.database import metadata, session
from elixir import *

class User(Entity):
    has_field('email', String)
    has_many('lists', of_kind='List')

class List(Entity):
    has_field('title', Unicode, nullable=False)
    belongs_to('user', of_kind='User')
    has_many('items', of_kind='Item')

class Item(Entity):
    has_field('value', Unicode, nullable=False)
    belongs_to('list', of_kind='List')

In this model, users are uniquely identified by their e-mail address and can have multiple lists. Lists have a title, an owner, and multiple items. Items have a value and their containing list.

See the Elixir documentation for help with defining and using your tables:

http://elixir.ematia.de/tutorial.html

For a comparison between SQLAlchemy and Elixir, see also:

http://cleverdevil.org/computing/61/sqlalchemy-and-elixir-at-pyatl-tonight