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Data Models
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Data models are responsible for all interactions with the database.

.. contents:: Page Contents

What is a Model?
================

**A model is...**

Architecture
============

Data model - handles the management of the data

Data object - represents one piece of actual data, and is used to read/write.

Notes on Data Object
^^^^^^^^^^^^^^^^^^^^

As of this writing, data objects are being converted in order to overload the '=' operator. Previously you had to use $obj->set()
to change the value. The object code would set a flag and the field would be updated in the database on the next save.

Now, rather than using set(), you can use the '=' operator. But there are side effects to be aware of, for example:

- If the extended data class uses additional members to extend the data, then they must be declared public for the desired behavior. As an
example, a Task_obj creates a member called sub_tasks. If not declared as public, then it will to into the internal $obj->_data member.
Sometimes this will not be a problem, however if you wanted to use sub_tasks in a foreach loop, then it won't work as expected. 

Deletion
========

Since there are many relationships to be aware of, let the data model architecture look after the details.

on_delete($id)
--------------

This is a callback function that you can define for any model. Basically, it allows you to get notified
before a record is actually deleted from the database, so that you can perform other updates.

Errors
======

If an error occurs in a model, it should set a message in public attribute $this->last_error.

Note that there is no requirement to clear this attribute, so it cannot be used to determine if an error occurred.
It should always be used in combination with a return code that indicates an error condition.