Chain rewriting model in magento

Question

I have installed a module in Magento 1.9 that rewrites a newsletter model from Magento Core. The config.xml file looks like this:

<models>
    <onestepcheckout>
        <class>MW_Onestepcheckout_Model</class>
        <resourceModel>onestepcheckout_mysql4</resourceModel>
    </onestepcheckout>

    <onestepcheckout_mysql4>
        <class>MW_Onestepcheckout_Model_Mysql4</class>
        <entities>
            <onestepcheckout>
                <table>mw_onestepcheckout</table>
            </onestepcheckout>
        </entities>
    </onestepcheckout_mysql4>

    <newsletter><!--newsletter-->
      <rewrite>                  
          <subscriber>MW_Onestepcheckout_Model_Subscriber</subscriber>                        
      </rewrite>            
    </newsletter>
</models>

Everything is working fine in this moment. The problem is when I want to rewrite this new class, because nothing happened. The config.xml is:

<models>
    <extendonestepcheckout>
        <class>Blugento_ExtendOneStepCheckout_Model</class>
    </extendonestepcheckout>

    <onestepcheckout>
        <rewrite>
            <subscriber>Blugento_ExtendOneStepCheckout_Model_Subscriber</subscriber>
        </rewrite>
    </onestepcheckout>
</models>

And the code from my new class is:

class Blugento_ExtendOneStepCheckout_Model_Subscriber extends MW_Onestepcheckout_Model_Subscriber
{
     public function  getCouponCode()
     {
         if(Mage::getConfig()->getNode('modules/JEGAN_EmailCoupon')) {
             $helperData = new JEGAN_EmailCoupon_Helper_Data();
             return $helperData->generateNewCouponCode('jeganemailtabmenu/jegannewsletteremailcoupon', $this->getCustomerId(), 1);
         }
     }
}

I've created a debugging file test.php and wrote this code inside:

include "app/Mage.php";
Mage::app();

$dModel = Mage::getModel('newsletter/subscriber');
var_dump(get_class($dModel));

This code displays on screen:

string(35) "MW_Onestepcheckout_Model_Subscriber"

but it should display:

string(47) "Blugento_ExtendOneStepCheckout_Model_Subscriber"

I don't know what it doesn't work, can you tell me if there is a problem with this code? Thank you!

Answer 1

Change this

<onestepcheckuot>
    <rewrite>
        <subscriber>Blugento_ExtendOneStepCheckout_Model_Subscriber</subscriber>
    </rewrite>
</onestepcheckuot>

to this:

<newsletter>
    <rewrite>
        <subscriber>Blugento_ExtendOneStepCheckout_Model_Subscriber</subscriber>
    </rewrite>
</newsletter>

and make your module depend on the MW_Onestepcheckout module.

How does this work.

When instantiating a model, magento like this Mage::getModel('newsletter/subscriber'); magento looks for the xml node models->newsletter.

if inside this node there is node rewrite->subscriber it will load the class specified in that node.
If not, it will build the class name based on what's after the slash /subscriber.
So if you want your class to be used you have to have the nodes like this newsletter/subscriber not onestepcheckout/subscriber.

It you were to instantiate the model like this Mage::getModel('onestepcheckout/subscriber') you code would work, but the core does not load the model like that.
But your class can still extend the third party module one and you get both functionalities. the one from the third party and your changes. Actually this is the standard way of resolving class rewrite conflicts in magento 1.

And you need to make your module depend on the third party one because the configs are merged for all modules and the modules are loaded in their dependency order.
So you need to make sure your config is merged after the third party one.
Short version: "The second mouse gets the cheese".