Part 5 - Models and ORM Basics
February 24, 2011 | in Magento Step by Step
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The implementation of a "Models Tier" is a huge part of any MVC framework. It represents the data of your application, and most applications are useless without data. Magento Models play an even bigger role, as they typically contain the "Business Logic" that's often relegated to the Controller or Helper methods in other PHP MVC frameworks.
Traditional PHP MVC Models
If the definition of MVC is somewhat fuzzy, the definition of a Model is even fuzzier. Prior to the wide adoption of the MVC pattern by PHP developers, data access was usually raw SQL statements and/or a SQL abstraction layer. Developers would write queries and not think too much about what objects they were modeling.
In this day and age, raw SQL is mostly frowned upon, but many PHP frameworks are still SQL centric. Models will be objects that provide some layer of abstraction, but behind the scenes developers are still writing SQL and/or calling SQL like abstraction methods to read and write-down their data.
Other frameworks eschew SQL and take the Object Relational Mapping (ORM) approach. Here, a developer is dealing strictly with Objects. Properties are set, and when a save method is called on the Object, the data is automatically written to the database. Some ORMs will attempt to divine object properties from the database, others require the user to specify them in some way, (usually in an abstract data language such as YAML). One of the most famous and popular implementations of this approach is ActiveRecord.
This definition of ORM should suffice for now, but like everything Computer Science these days, the strict definition of ORM has blurred over the years. It's beyond the scope of this article to settle that dispute, but suffice it say we're generalizing a bit.
Magento Models
It should be no surprise that Magento takes the ORM approach. While the Zend Framework SQL abstractions are available, most of your data access will be via the built in Magento Models, and Models you build yourself. It should also come as no surprise that Magento has a highly flexible, highly abstract, concept of what a Model is.