Question

To migrate all changes to all environments I use database upgrade scripts. I use them to create different instances(customer, tax settings etc.) but usually to migrate static blocks and config settings.

To migrate static blocks:

<?php
$block = Mage::getModel('cms/block');
$data = array(
   'title' => 'Block title',
   'identifier' => 'block_identifier',
   'content' => 'block content',
   'is_active' => 1,
   'stores' => array(0 => Mage_Core_Model_App::ADMIN_STORE_ID),
);

$block->addData($data);
$block->save();
?>

To migrate settings:

<?php
Mage::getModel('core/config')->saveConfig('design/theme/default', 'theme');
?>

I know that we can modify Magento settings via config.xml:

<default>
    <general>
        <store_information>
            <name>My Store</name>
        </store_information>
        <content_staging>
            <block_frontend_stub>home</block_frontend_stub>
        </content_staging>
    </general>
</default>

But as far as I understand we can modify settings in such way only if paths: general/store_information/name
and
general/content_staging/block_frontend_stub
don’t exists at db or their values equal NULL, if value not NULL we can’t modify it via xml. I tested it on my local environment and I think I’m right but can’t find a code at Magento which is responsible for setting configuration via xml.
Am I right?

Can you show me the part of code which is responsible for it?
And what is your best migration practices for Magento? Maybe I don’t know something 🙂

Answer 1

You are right, values specified in the config xml files are overwritten by values from the core_config_data table.
As B00MER pointed out, the code in question is in Mage_Core_Model_Config::init():

public function init($options=array())
{
    $this->setCacheChecksum(null);
    $this->_cacheLoadedSections = array();
    $this->setOptions($options);
    $this->loadBase();

    $cacheLoad = $this->loadModulesCache();
    if ($cacheLoad) {
        return $this;
    }
    $this->loadModules();
    $this->loadDb();
    $this->saveCache();
    return $this;
}

Notice that loadDb() is called after loadModules().
The actual merging logic is in the config resource model Mage_Core_Model_Resource_Config::loadToXml().

For each global setting this is called:

$xmlConfig->setNode('default/' . $r['path'], $value);

For each website scope setting this is called:

$nodePath = sprintf('websites/%s/%s', $websites[$r['scope_id']]['code'], $r['path']);
$xmlConfig->setNode($nodePath, $value);

For each website scope setting this is called:

$nodePath = sprintf('stores/%s/%s', $stores[$r['scope_id']]['code'], $r['path']);
$xmlConfig->setNode($nodePath, $value);

This is slightly simplified, but if you need more detail you can look at the source.