Clio Models
===========

The next step is to define Clio models. A Clio model is a class that
is going to be mapped to a table by the SQLAlchemy ORM. A Clio model
also has a number of special methods that can be used to drive the
workflow process and that will be described later.

It is easy to create a Clio-based model, just subclass from
``clio.Model``::

  import clio

  class Address(clio.Model):
      pass

In many cases, a ``clio.Model`` needs to define its own
``__init__``. This looks like this::

  class Address(clio.Model):
      def __init__(self, code, street, city, country):
          super(Address, self).__init__(code)
          self.street = street
          self.city = city
          self.country = country

Note that it is required to call the superclass and pass it the
``code``.

Mapping
-------

After definining the tables and the model classes, we use the normal
SQLAlchemy object relational mapper to map the classes to the tables::

  from sqlalchemy.orm import mapper

  mapper(Address, address_table)

This is standard SQLAlchemy, and we have seen everything needed to
create a Clio-managed model. The situation becomes a bit more involved
when we want to create relations between models.

Workflow properties
-------------------

The Clio table columns described earlier will exist on the mapped
instances. The following properties are available:

id 
  An integer attribute uniquely identifying the record underlying the
  instance. Will be automatically set by the system.

code
  An integer that uniquely identifies the actual information managed
  this object. Other versions of this object in other workflow states
  will have the same ``code``, but not the same ``id``.

status
  An integer that indicates the workflow status that the particular
  version is in.

workflow_timestamp
  The moment this version last underwent a workflow transition.

creation_timestamp
  The moment this object was created.