Models and ResourceModels

AllMagento models extend the base Mage_Core_Model_Abstract class. This class helps any model save itself to the database in a straight property-to-column name manner.
The model, when saving, calls up its own resource singleton and passes itself ($this) to the resource’s save method. The resource is then scripted to collect any values from the model’s internal _data array and prepare an insert or an update statement with those values.

Model’s have a _getResource method which retrieves a previously setup resource.This resource is initialized by the init method using a resource name of the pattern module_name. The name portion of that pattern represents the final portion of a class name. The prefix of the class name is specified by a portion of the XML in the module’s etc/config.xml. If class names have the term Mysql4 in their names, they are generally straight model resources.

If the word Entity appears in the class name, then the resource is an EAV Entity. Let’s look at the Wishlist module as an example. In the config.xml of the wishlist modulewe see a resourceModel tag under themain definition of models. The value of this resourceModel tag points to another XML tag under the models tag. The class tag of this new definition specifies the class name prefix for any resource of this module. The following code shows how the sample XML file would produce a resource for the wishlist module.

$wish = Mage::getResourceSingleton(’wishlist/wishlist’);
echo get_class($wish);
//outputs: Mage_Wishlist_Model_Mysql4_Wishlist
…
<global>
<models>
<wishlist>
<class>Mage_Wishlist_Model</class>
<resourceModel>wishlist_mysql4</resourceModel>
</wishlist>
<wishlist_mysql4>
<class>Mage_Wishlist_Model_Mysql4</class>
<entities>
<wishlist>
<table>wishlist</table>
</wishlist>
<item>
<table>wishlist_item</table>
</item>
</entities>
</wishlist_mysql4>
…