Custom Admin Grid Column Renderer

Often, you'll want to add a column to a collection used in a grid, and to do so you'd use _prepareCollection():

protected function _prepareCollection()
{
    $collection = Mage::getResourceModel($this->_getCollectionClass());
  ...

Using the database to inspect EAV-based entity types can be a real pain in the ass, so here are a bunch of queries that let you inspect some popular EAV entity types easily. This practice can be applied to any EAV entity type, however as there are...

Handy for adding an attribute to a product or category which needs a custom frontend input type.

Much easier to show how this is done by showing you some code examples, so please see the link attached.

Declare an admin layout XML file for your module in your config.xml:

<config>
    <adminhtml>
        <layout>
            <updates>
                <your_module>
                    <file>your-module.xml</file>
    ...

Frontend With Route:

<config>
    <frontend>
        <routers>
            <namespace_module>
                <use>standard</use>
                <args>
                    <module>Namespace_Module</module>
       ...

Frontend:

<config>
    <frontend>
        <layout>
            <updates>
                <namespace_module>
                    <file>namespace-module.xml</file>
                </namespace_module>
            </up...