Author: 芳草苑主

今天碰到个问题百思不得其解。起因是我在改进 Magento rcah module 时，想在 category/index/view 输出前修改 head block 里其中一个 item: link_rel。

具体说来，我想调用 $headBlock->removeItem()->addLinkRel() 把修改过的 link_rel 添加到 head block 的 $_data[‘items’]。由于调用在 renderLayout() 之后，所以 head 在输出时仍然是修改前的 link_rel。这本不奇怪；奇怪的是，我观察到 $headBlock->getCssJsHtml() 在整个过程中只执行了一次，而且是在 $headBlock->removeItem()->addLinkRel() 之后，$headBlock->getCssJsHtml() 应该是跟 html 输出直接相关，为什么在 $headBlock->getCssJsHtml() 看来 link_rel 还是原值？

Layout rendering 机制对我来说还比较神秘。我只能暂时这么解释：

renderLayout() 时把所有 block 的状态记住了，所以此后再怎么修改 block 的状态都无济于事。到了输出 html 阶段，所有的输出都是以 renderLayout() 时的 block。

BTW，在 rcah 模块中，我找到一个非常巧妙的办法来修改 link_rel （canonical link 的值），完全绕过了跟 head block 的纠缠。

In previous version of rcah module, if “Use Canonical Link Meta Tag For Categories” is enabled in System >> Configuration >> Catalog >> Search Engine Optimizations,

and if you set a root category as homepage, the homepage html head outputs a link like

<link rel=”canonical” href=”http://MY_DOMAIN/catalog/category/view/s/URL_KEY/id/ROOT_CATEGORY_ID/” />

or if you set a subcategory as homepage (System -> Configuration -> General -> Web -> Default Pages -> Default web URL set to “rcah/index/index/id/SUBCATEGORY_ID”), the homepage html head outputs a link like

<link rel=”canonical” href=”http://MY_DOMAIN/REWRITED_URL” />

In the first scenario, the canonical link is invalid because Magento native code won’t allow root category page be accessed. In the second scenario, the canonical link is valid, but it should be “http://MY_DOMAIN/” in either scenario.

Release 0.2.0 is to fix this problem. Download RootCategoryAsHomepage.tar.gz

Just for your interest, I was going to write IndexController like this to fix the problem.

/**
* most code is from CategoryController::viewAction()
*
* run _modifyCanonial() before render layout
*/
public function indexAction()
{
if ($category = $this->_initCatagory()) {

Mage::getModel('catalog/design')->applyDesign($category, Mage_Catalog_Model_Design::APPLY_FOR_CATEGORY);
Mage::getSingleton('catalog/session')->setLastViewedCategoryId($category->getId());

$update = $this->getLayout()->getUpdate();
$update->addHandle('default');

if (!$category->hasChildren()) {
$update->addHandle('catalog_category_layered_nochildren');
}

$this->addActionLayoutHandles();

$update->addHandle($category->getLayoutUpdateHandle());
$update->addHandle('CATEGORY_'.$category->getId());



if ($category->getPageLayout()) {
$this->getLayout()->helper('page/layout')
->applyHandle($category->getPageLayout());
}

$this->loadLayoutUpdates();

$update->addUpdate($category->getCustomLayoutUpdate());

$this->generateLayoutXml()->generateLayoutBlocks();

if ($category->getPageLayout()) {
$this->getLayout()->helper('page/layout')
->applyTemplate($category->getPageLayout());
}

if ($root = $this->getLayout()->getBlock('root')) {
$root->addBodyClass('categorypath-'.$category->getUrlPath())
->addBodyClass('category-'.$category->getUrlKey());
}

$this->_initLayoutMessages('catalog/session');
$this->_initLayoutMessages('checkout/session');
$this->_modifyCanonial()->renderLayout();
}
elseif (!$this->getResponse()->isRedirect()) {
$this->_forward('noRoute');
}
}

/***
* Find link_rel item in items of head, and modify it
*
* Each item is array of 5 in a format like
* array('type'=>'link_rel',
*         'name'=>'http://domain/path',
*         'params'=>'rel="canonical"',
*         'if'=>null,
*         'cond'=>null);
*/
protected function _modifyCanonial() {
if ($headBlock = $this->getLayout()->getBlock('head')) {
$items = $headBlock->getData('items');
foreach ($items as $key => $value) {
if (false !== strpos($key, 'link_rel')) {
if ($value['type'] == 'link_rel' && $value['params'] == 'rel="canonical"') {
$value['name'] = Mage::getUrl();
$items[$key] = $value;
$headBlock->setData('items', $items);
break;
}

}
}
}
return $this;
}

However, just before release, I found a much better way: just use setCategoryUrl in _initCatagory(). So now IndexController is now as:

protected function _initCatagory()
{
Mage::dispatchEvent('catalog_controller_category_init_before', array('controller_action'=>$this));
$rootCategoryId = Mage::app()->getStore()->getRootCategoryId();
$categoryId = (int) $this->getRequest()->getParam('id', $rootCategoryId);
if (!$categoryId) {
return false;
}

$category = Mage::getModel('catalog/category')
->setStoreId(Mage::app()->getStore()->getId())
->load($categoryId)
//force url as a homepage url to work with canonical link
->setUrl(Mage::getUrl());

if ($categoryId == $rootCategoryId) {
//do nothing. bypass canshow test for root category
}
elseif (!Mage::helper('catalog/category')->canShow($category)) {
return false;
}
Mage::getSingleton('catalog/session')->setLastVisitedCategoryId($category->getId());
Mage::register('current_category', $category);
try {
Mage::dispatchEvent('catalog_controller_category_init_after', array('category'=>$category, 'controller_action'=>$this));
} catch (Mage_Core_Exception $e) {
Mage::logException($e);
return false;
}
return $category;
}

public function indexAction() {
parent::viewAction();
}