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Magento – multiple classes extending same core class

I’m sure we’ve all run into a situation where you have multiple extensions with a block or model that rewrites the same core block/model. The problem I’ve run into is this: How do you control the order in which Magento sees these classes?

For example, let’s say we have 2 extensions with the following 2 classes:

Class A

config.xml

<catalog>
    <rewrite>
        <product_view>My_ClassA_Block_Catalog_Product_View</product_view>
    </rewrite>
</catalog>

My/ClassA/Block/Catalog/Product/View.php

class My_ClassA_Block_Catalog_Product_View extends Mage_Catalog_Block_Product_View {}

Class B

<catalog>
    <rewrite>
        <product_view>My_ClassB_Block_Catalog_Product_View</product_view>
    </rewrite>
</catalog>

My/ClassB/Block/Catalog/Product/View.php

class My_ClassB_Block_Catalog_Product_View extends Mage_Catalog_Block_Product_View {}

–

The recommended solution is to change one of them so they extend the other and chain them together (class A extends B {}, class B extends C {}, etc):

My/ClassA/Block/Catalog/Product/View.php

class My_ClassA_Block_Catalog_Product_View extends My_ClassB_Block_Catalog_Product_View {}

My/ClassB/Block/Catalog/Product/View.php

class My_ClassB_Block_Catalog_Product_View extends Mage_Catalog_Block_Product_View {}

–

The problem I’ve run into is that Magento doesn’t necessarily see it that way. I don’t know if it’s alphabetical or somewhat random, but sometimes this works and sometimes it doesn’t. In some cases, Magento gives priority to ClassB and all calls to createBlock('catalog/product_view') create an instance of ClassB, completely bypassing any code in ClassA.

So my question is this: How do I control which class gets instantiated by createBlock('catalog/product_view') when 2 different extensions both rewrite the core catalog_product_view class?

Magento – multiple classes extending same core class

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