• app/code/local/Magestore/Newmodule/Block/Product/List
• app/code/local/Magestore/Newmodule/etc/config.xml
• app/etc/modules/Magestore_Newmodule.xml

• Step1: Declare the module (app/etc/modules/Magestore_Newmodule.xml) as in Configuration XML (in the last post) > Create and register a module.

• Step 2: Edit the file config.xml (app/code/local/Magestore/Newmodule/etc/config.xml)

<config>
 <global>
    <blocks>
      <newmodule>
       <class>Magestore_Newmodule_Block</class>
      </newmodule>
      <catalog>
        <rewrite>
              <product_list>Magestore_Newmodule_
              Block_List</product_list>
        </rewrite>
      </catalog>
    </blocks>
  </global>
</config> 

Through this step, when you call the block ‘catalog/product_list’ the system will return a block ‘newmodule/list’.

• Step 3: Override block (app/code/local/Magestore/Newmodule/Block/List.php)

<?php
Class Magestore_Newmodule_Block_List extends Mage_Catalog_Block_Product_List{
 // function (need be written)
 protected function_getProductCollection(){
   //custom code
   }
}

II – For Model
For instance: override app/code/core/Mage/Catalog/Model/Product.php)
By the file app/code/local/Magestore/Newmodule/Model/Catalog/Product.php
• Step 1: Create and register a new module (as same as the part above)
• Step 2: File config.xml(app/code/local/Magestore/Newmodule/config.xml)

<config>
 <global>
    <models>
      <newmodule>
       <class>Magestore_Newmodule_Helper</class>
      </newmodule>
      <catalog>
        <rewrite>
              <product_list>Magestore_Newmodule_Model_
              Product</product_list>
        </rewrite>
     </catalog>
    </models>
  </global>
</config> 

• Step3: Override model (app/code/local/Magestore/Newmodule/Model/Catalog/Product.php)

<?php
class Magestore_Newmodule_Model_Product extends Mage_Catalog_Model_Product_List
{ 

         public function isSalable(){
         }
}

III – For Resource Models

For example: override app/code/core/Mage/Catalog/Model/Resource/Eav/Mysql4/Attribute.php)

By the file: app/code/local/Magestore/Newmodule/Model/Catalog/Resource/Eav/Mysql4/Attribute.php

• Step 1: Create and register a new module (as same as the previous part)

• Step 2: File config.xml(app/code/local/Magestore/Newmodule/config.xml)

<config>
 <global>
    <models>
      <newmodule>
       <class>Magestore_Newmodule_Model</class>
      </newmodule>
      <catalog_resource_eav_mysql4>
        <rewrite>
            <attribute> Magestore_Newmodule_
            Model_Catalog_Resource_Eav_Mysql4
            _Attribute </attribute>
        </rewrite>
     < catalog_resource_eav_mysql4>
    </models>
  </global>
</config> 

• Step 3: Override file (as same as the way to conduct with Model)

IV – For Helper

For example: override app/code/core/Mage/Catalog/Helper/Data.php)

By the file app/code/local/Magestore/Newmodule/Helper/Catalog/Data.php

• Step 1: Create and register a new module (as same as the part above).

• Step 2: File config.xml(app/code/local/Magestore/Newmodule/config.xml)

<config>
 <global>
    <helpers>
      <newmodule>
       <class>Magestore_Newmodule_Model</class>
      </newmodule>
      < catalog>
        <rewrite>
             <data> Magestore_Newmodule_Helper_
             Catalog_Data </data>
        </rewrite>
     <catalog >
    </helpers>
  </global>
</config> 

• Step 3: Override helper (app/code/local/Magestore/Newmodule/Helper/Catalog/Data.php)

<?php
class Magestore_Newmodule_Helper_Product_Catalog_Data extends Mage_Catalog_Helper_Data
{ 

       public function getLastViewed(){
       }
}

V – Notices

Rewriting Modules/Resource models/Helper/Block only has impact on calling objects through Mage classes such as: Mage::getModel(), Mage::getResourceModel(), Mage::helper(), Mage::getSingletonBlock(). With the generation of objects from different ways as new ($product = new Mage_Catalog_Model_Product(); ) or extends rewriting does not have influence. This is exactly the difference when we use direct object-calling from class name and the function which Magento provides.

VI – Questions

Question: Can overriding a resource model be conducted as same as overriding a normal model (because they are belong to the model area)?

Answer: You cannot configure the override of a resource model as same as a normal model. Because the override only has influence when the system calls the function Mage::getResourceModel(). This function reads the configuration rewrite from the bar of the resource model (for example: catalog_resource_eav_mysql4) but from the bar of the model.

Hope it is useful for you as for me!