custom model magento looks in Mage/…?

Question

I try to follow this tutorial: http://devdocs.magento.com/guides/m1x/magefordev/mage-for-dev-5.html

Problem is it doesn't work at all as Magento always tries to load the model from the wrong folder

Warning: include(Mage/My/Module/Model/Resource/Blogpost.php)

Here is my config.xml. The part with overwriting the success page works like a charm.

<?xml version="1.0"?>
<config>
    <modules>
        <my_module>
            <version>1.0.0</version>
        </my_module>
    </modules>
    <frontend>
        <routers>
            <my_module>
                <use>standard</use>
                <args>
                    <module>My_Module</module>
                    <frontName>my_module</frontName>
                </args>
            </my_module>
        </routers>
        <layout>
            <updates>
                <my_module>
                    <file>module.xml</file>
                </my_module>
            </updates>
        </layout>
    </frontend>
    <global>
        <blocks>
            <my_module>
                <class>My_Module_Block</class>
            </my_module>
            <checkout>
                <rewrite>
                    <onepage_success>My_Module_Block_Onepage_Success</onepage_success>
                </rewrite>
            </checkout>
        </blocks>
    </global>
    <models>
        <my_module>
            <class>My_Module_Model</class>
            <resourceModel>my_module_resource</resourceModel>
        </my_module>
    </models>
</config>

Answer 1

Your <models> node needs to be inside the <global> node. Like you did for the <blocks> node:

<global>
        <blocks>
            <my_module>
                <class>My_Module_Block</class>
            </my_module>
            <checkout>
                <rewrite>
                    <onepage_success>My_Module_Block_Onepage_Success</onepage_success>
                </rewrite>
            </checkout>
        </blocks>
        <models>
            <my_module>
                <class>My_Module_Model</class>
                 <resourceModel>my_module_resource</resourceModel>
            </my_module>
        </models>
    </global>

Answer 2

Move :

<models>
    <my_module>
        <class>My_Module_Model</class>
        <resourceModel>my_module_resource</resourceModel>
    </my_module>
</models>

To, <global>

<global>
    <blocks>
        <my_module>
            <class>My_Module_Block</class>
        </my_module>
        <checkout>
            <rewrite>
                <onepage_success>My_Module_Block_Onepage_Success</onepage_success>
            </rewrite>
        </checkout>
    </blocks>
    <models>
        <my_module>
            <class>My_Module_Model</class>
            <resourceModel>my_module_resource</resourceModel>
        </my_module>
    </models>
</global>