Extend Mage_Sales_Model_Order

how do i start ? hrmmmm. ok , right now Im trying to extend the mage_sales_mode_order . but this error appear. Fatal error: Call to a member function load() on a non-object in /app/code/core/Mage/Adminhtml/controllers/Sales/OrderController.php on line 74

i don't know what is the problem because i already try using the same code extend different magento site but is working. but below is what that i do and thanks in advance.

MageCustom/Sales/Model/Order.php

class MageCustom_Sales_Model_Order extends Mage_Sales_Model_Order
{

public function queueNewOrderEmail($forceMode = false)
{
    $storeId = $this->getStore()->getId();


    if (!Mage::helper('sales')->canSendNewOrderEmail($storeId)) {
        return $this;
    }

    // Get the destination email addresses to send copies to
    $copyTo = $this->_getEmails(self::XML_PATH_EMAIL_COPY_TO);
    $copyMethod = Mage::getStoreConfig(self::XML_PATH_EMAIL_COPY_METHOD, $storeId);

    // Start store emulation process
    /** @var $appEmulation Mage_Core_Model_App_Emulation */
    $appEmulation = Mage::getSingleton('core/app_emulation');
    $initialEnvironmentInfo = $appEmulation->startEnvironmentEmulation($storeId);

    try {
        // Retrieve specified view block from appropriate design package (depends on emulated store)
        $paymentBlock = Mage::helper('payment')->getInfoBlock($this->getPayment())
            ->setIsSecureMode(true);
        $paymentBlock->getMethod()->setStore($storeId);
        $paymentBlockHtml = $paymentBlock->toHtml();
    } catch (Exception $exception) {
        // Stop store emulation process
        $appEmulation->stopEnvironmentEmulation($initialEnvironmentInfo);
        throw $exception;
    }

    // Stop store emulation process
    $appEmulation->stopEnvironmentEmulation($initialEnvironmentInfo);

    // Retrieve corresponding email template id and customer name
    if ($this->getCustomerIsGuest()) {
        $templateId = Mage::getStoreConfig(self::XML_PATH_EMAIL_GUEST_TEMPLATE, $storeId);
        $customerName = $this->getBillingAddress()->getName();
    } else {
        $templateId = Mage::getStoreConfig(self::XML_PATH_EMAIL_TEMPLATE, $storeId);
        $customerName = $this->getCustomerName();
    }

    /** @var $mailer Mage_Core_Model_Email_Template_Mailer */
    $mailer = Mage::getModel('core/email_template_mailer');
    /** @var $emailInfo Mage_Core_Model_Email_Info */
    $emailInfo = Mage::getModel('core/email_info');
    $emailInfo->addTo($this->getCustomerEmail(), $customerName);
    if ($copyTo && $copyMethod == 'bcc') {
        // Add bcc to customer email
        foreach ($copyTo as $email) {
            $emailInfo->addBcc($email);
        }
    }
    $mailer->addEmailInfo($emailInfo);

    // Email copies are sent as separated emails if their copy method is 'copy'
    if ($copyTo && $copyMethod == 'copy') {
        foreach ($copyTo as $email) {
            $emailInfo = Mage::getModel('core/email_info');
            $emailInfo->addTo($email);
            $mailer->addEmailInfo($emailInfo);
        }
    }

    // Set all required params and send emails
    $mailer->setSender(Mage::getStoreConfig(self::XML_PATH_EMAIL_IDENTITY, $storeId));
    $mailer->setStoreId($storeId);
    $mailer->setTemplateId($templateId);
    $mailer->setTemplateParams(array(
        'order'        => $this,
        'billing'      => $this->getBillingAddress(),
        'payment_html' => $paymentBlockHtml
    ));

    /** @var $emailQueue Mage_Core_Model_Email_Queue */
    $emailQueue = Mage::getModel('core/email_queue');
    $emailQueue->setEntityId($this->getId())
        ->setEntityType(self::ENTITY)
        ->setEventType(self::EMAIL_EVENT_NAME_NEW_ORDER)
        ->setIsForceCheck(!$forceMode);

    //$mailer->setQueue($emailQueue)->send();
    $mailer->send();
    Mage::log('new order trigger email', null, 'email.log');

    $this->setEmailSent(true);
    $this->_getResource()->saveAttribute($this, 'email_sent');

    return $this;
}

MageCustom/Sales/etc/config.xml

<config>
    <modules>
        <MageCustom_Sales>
            <version>0.1.0</version>
        </MageCustom_Sales>
    </modules>
    <global>
        <models>
            <MageCustom_Sales>
                <class>MageCustom_Sales_Model</class>
            </MageCustom_Sales>
            <sales>
                <rewrite>
                    <order>MageCustom_Sales_Model_Order</order>
                </rewrite>
            </sales>   
        </models>
    </global>
</config>

MageCustom_Sales.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <MageCustom_Sales>
            <active>false</active>
            <codePool>local</codePool>
        </MageCustom_Sales>
    </modules>
</config>

Solution

Problem

Your class and configuration are all correct assuming they exist in app/code/local, except for the active setting in MageCustom_Sales.xml:

<active>false</active>

Turn it on, clear your cache and try again :)

Testing

> With Magerun

If you've got magerun, you can use it to test your rewrite:

n98-magerun.phar dev:class:lookup model sales/order
# Model sales/order resolves to MageCustom_Sales_Model_Order

If you don't see the above resolution, you may have conflicts with the rewrite, but it's more likely that your rewrite configuration is wrong.

If you don't have Magerun - get it! You won't regret it.

> Without Magerun

You can drop a custom script into the root directory of your Magento project just to test the class alias:

<?php
include 'app/Mage.php';
Mage::app();
var_dump(get_class(Mage::getModel('sales/order')));

Run it from command line via php myTestFile.php, or from browser via http://magento.local/myTestFile.php.

If it works, you should see string(28) "MageCustom_Sales_Model_Order". If it doesn't you'll see bool(false).

Hope this helps.