Add Custom Attribute for products in custom Attributes set

addProductAttribute.php

<!-- local/Namespace/Catalog/data/Namespace_catalog_setup/data-install-0.0.1.php -->
<?php

try {

    /* @var $installer Mage_Catalog_Model_Resource_Setup */
    $installer = $this;

    /**
     * Custom attribute creation
     */
    $installer->addAttribute(Mage_Catalog_Model_Product::ENTITY, 'my_custom_attribute', array(
        /** let group empty to avoid adding attribute to all Attribute Sets if you have several Attribute Sets **/
        /** otherwise you can set "General" for example **/
            'group'             => '', 
            'type'              => 'varchar',
            'backend'           => '',
            'frontend'          => '',
            'label'             => 'My Custom Attribute',
            'input'             => 'text',
            'source'            => '',
            'global'            => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
            'user_defined'      => true, /** Define this property in order to avoid that this attribute is set un general group */
            'visible'           => true,
            'required'          => false,
            'visible_on_front'  => true,
            'used_in_product_listing' => false,
            'unique'            => false,
            'is_configurable'   => false,
            'apply_to'          => Mage_Catalog_Model_Product_Type::TYPE_SIMPLE,
        )
    );
    
     $installer->addAttribute(Mage_Catalog_Model_Product::ENTITY, 'my_custom_attribute_bool', array(
            'group' => '',
            /** Let type empty in order to enable this attribute filterable , by default the booleans are not allowed
            to be filterable, we have to update this custom attribute later to set his backend_type **/
            'type' => '',
            'backend' => '',
            'frontend' => '',
            'label' => 'my custom label',
            'input' => 'select',
            'source' => 'eav/entity_attribute_source_boolean',
            'global' => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
            'user_defined' => true, /** Define this property in order to avoid that this attribute is set un general group */
            'visible' => true,
            'required' => false,
            'visible_on_front' => true,
            'used_in_product_listing' => true,
            'unique' => false,
            'is_configurable' => false,
            'apply_to' => Mage_Catalog_Model_Product_Type::TYPE_SIMPLE,
        )
    );
    

    /**
     *  Attributes sets creation
     */
    $defaultAttributeSetId = $installer->getAttributeSetId(Mage_Catalog_Model_Product::ENTITY, 'default');

    $entityTypeId = $installer->getEntityTypeId(Mage_Catalog_Model_Product::ENTITY);

    // Attribute sets names
    $custom1AttributeSetName = 'Custom1 - Set - Attribute';
    $custom2AttributeSetName = 'Custom2 - Set - Attribute';

    $attributeSetNames = array(
        $custom1AttributeSetName,
        $custom2AttributeSetName,
    );
    
// let's create our attributes set
    foreach ($attributeSetNames as $attributeSetName) {
        $model  = Mage::getModel('eav/entity_attribute_set')->setEntityTypeId($entityTypeId);
        $model->setAttributeSetName($attributeSetName);

        if ($model->validate()) {
            $model->save();
            $model->initFromSkeleton($defaultAttributeSetId);
            $model->save();
        }
    }
    
    /**
     * Attributes binding to attribute sets
     */

    foreach($attributeSetNames as $attributeSetName){
        //get AttributeSetId for each AttributeSet create above
        $attributeSetId = $installer->getAttributeSetId(Mage_Catalog_Model_Product::ENTITY, $attributeSetName);
        
        // $groupId can be for example 'General, Prices ...'
        // In our case we call method getDefaultAttributeGroupId(), it returns 'general'
        $groupId = $installer->getDefaultAttributeGroupId(Mage_Catalog_Model_Product::ENTITY, $installer->getAttributeSetId(Mage_Catalog_Model_Product::ENTITY, $attributeSetName));
 
        //OR
        //Target directly a attribute_group_id
        $groupId = $installer->getAttributeGroupId(Mage_Catalog_Model_Product::ENTITY, $installer->getAttributeSetId(Mage_Catalog_Model_Product::ENTITY, $attributeSetName),'my attribute group name');
 
        // If your attribute group is not created yet.
        $installer->addAttributeGroup(Mage_Catalog_Model_Product::ENTITY, $attributeSetId, 'my attribute group name', 100);
        
        //add Attribute in the catalog_product entity, in the right attributeSet, in the right Group, with our Custom Attribute Id
        $installer->addAttributeToGroup(Mage_Catalog_Model_Product::ENTITY, $attributeSetId, $groupId, $installer->getAttributeId(Mage_Catalog_Model_Product::ENTITY, 'my_custom_attribute'));
    }

    
    /**
    * Notice :
    * instead of use $attributeSetId we can also use directly the customAttributeSetName, Magento will retrieve the right Id 
    * check Mage_Eav_Model_Entity_Setup
    * 
    * Same thing for attribute. Use attribute name is possible, Magento will retrieve the right Attribute Id
    **/
    
    $installer->addAttributeToGroup(Mage_Catalog_Model_Product::ENTITY, $custom1AttributeSetName, $groupId, 'my_custom_attribute');

    /** Here we update our boolean attribute **/
    $installer->updateAttribute(Mage_Catalog_Model_Product::ENTITY,'my_custom_attribute_bool','backend_type','int');


} catch (Exception $e) {
    // Silence is golden
    Mage::logException($e);
}

Namespace_Catalog_etc_config.xml

<!-- declare resources for setup -->
<?xml version="1.0" encoding="utf-8"?>
<config>
  <global>
       <resources>
          <namespace_catalog_setup>
              <setup>
                  <module>Namespace_Catalog</module>
                      <class>Mage_Catalog_Model_Resource_Setup</class>
              </setup>
              <connection>
                  <use>core_setup</use>
              </connection>
          </namespace_catalog_setup>
      </resources>
    </global>
</config>