Magento模块调用的过程和逻辑

1.在调用每个Magento模块(Modules)的时候，首先会返回Mage_Core_Model_Config 这个模型 它里面呈现了模块的一些常规配置，比如是否生效(enabled)，版本(version)等等。Mage_Core_Model_Congif这个模型中有这么一个方法，来完成上面所说的功能。

    /**
     * Get module config node
     *
     * @param string $moduleName
     * @return Varien_Simplexml_Object
     */
    function getModuleConfig($moduleName='')
    {
        $modules = $this->getNode('modules');
        if (''===$moduleName) {
            return $modules;
        } else {
            return $modules->$moduleName;
        }
    }

这个方法有一个参数，就是模块名，返回的对象是Varien_Simplexml_Object2.调用每个模块的时候，它只是会建立一个基本的结构，并不会调用模块自身的配置情况。_loadDeclaredModules这个方法来帮助完成上面所说的需求。

 /**
     * Load declared modules configuration
     *
     * @param   null $mergeConfig depricated
     * @return  Mage_Core_Model_Config
     */
    protected function _loadDeclaredModules($mergeConfig = null)
    {
        $moduleFiles = $this->_getDeclaredModuleFiles();
        if (!$moduleFiles) {
            return ;
        }

        Varien_Profiler::start('config/load-modules-declaration');

        $unsortedConfig = new Mage_Core_Model_Config_Base();
        $unsortedConfig->loadString('');
        $fileConfig = new Mage_Core_Model_Config_Base();

        // load modules declarations
        foreach ($moduleFiles as $file) {
            $fileConfig->loadFile($file);
            $unsortedConfig->extend($fileConfig);
        }

        $moduleDepends = array();
        foreach ($unsortedConfig->getNode('modules')->children() as $moduleName => $moduleNode) {
            if (!$this->_isAllowedModule($moduleName)) {
                continue;
            }

            $depends = array();
            if ($moduleNode->depends) {
                foreach ($moduleNode->depends->children() as $depend) {
                    $depends[$depend->getName()] = true;
                }
            }
            $moduleDepends[$moduleName] = array(
                'module'    => $moduleName,
                'depends'   => $depends,
                'active'    => ('true' === (string)$moduleNode->active ? true : false),
            );
        }

        // check and sort module dependence
        $moduleDepends = $this->_sortModuleDepends($moduleDepends);

        // create sorted config
        $sortedConfig = new Mage_Core_Model_Config_Base();
        $sortedConfig->loadString('');

        foreach ($unsortedConfig->getNode()->children() as $nodeName => $node) {
            if ($nodeName != 'modules') {
                $sortedConfig->getNode()->appendChild($node);
            }
        }

        foreach ($moduleDepends as $moduleProp) {
            $node = $unsortedConfig->getNode('modules/'.$moduleProp['module']);
            $sortedConfig->getNode('modules')->appendChild($node);
        }

        $this->extend($sortedConfig);

        Varien_Profiler::stop('config/load-modules-declaration');
        return $this;
    }

从foreach ($moduleDepends as $moduleProp) 开始的这段代码可以看出，程序是对app\etc\modules这段代码做xml的解析3.loadBase()这个方法会对系统的配置文件进行加载和解析，比如config.xml和local.xml

    /**
     * Load base system configuration (config.xml and local.xml files)
     *
     * @return Mage_Core_Model_Config
     */
    public function loadBase()
    {
        $etcDir = $this->getOptions()->getEtcDir();
        $files = glob($etcDir.DS.'*.xml');
        $this->loadFile(current($files));
        while ($file = next($files)) {
            $merge = clone $this->_prototype;
            $merge->loadFile($file);
            $this->extend($merge);
        }
        if (in_array($etcDir.DS.'local.xml', $files)) {
            $this->_isLocalConfigLoaded = true;
        }
        return $this;
    }

4.此后加载模块自身的配置由loadModulesConfiguration这个function来完成

    /**
     * Iterate all active modules "etc" folders and combine data from
     * specidied xml file name to one object
     *
     * @param   string $fileName
     * @param   null|Mage_Core_Model_Config_Base $mergeToObject
     * @return  Mage_Core_Model_Config_Base
     */
    public function loadModulesConfiguration($fileName, $mergeToObject = null, $mergeModel=null)
    {
        $disableLocalModules = !$this->_canUseLocalModules();

        if ($mergeToObject === null) {
            $mergeToObject = clone $this->_prototype;
            $mergeToObject->loadString('');
        }
        if ($mergeModel === null) {
            $mergeModel = clone $this->_prototype;
        }
        $modules = $this->getNode('modules')->children();
        foreach ($modules as $modName=>$module) {
            if ($module->is('active')) {
                if ($disableLocalModules && ('local' === (string)$module->codePool)) {
                    continue;
                }
                if (!is_array($fileName)) {
                    $fileName = array($fileName);
                }

                foreach ($fileName as $configFile) {
                    $configFile = $this->getModuleDir('etc', $modName).DS.$configFile;
                    if ($mergeModel->loadFile($configFile)) {
                        $mergeToObject->extend($mergeModel, true);
                    }
                }
            }
        }
        return $mergeToObject;
    }

5.最后的解析工作由loadFile来完成

    /**
     * Imports XML file
     *
     * @param string $filePath
     * @return boolean
     */
    public function loadFile($filePath)
    {
        if (!is_readable($filePath)) {
            //throw new Exception('Can not read xml file '.$filePath);
            return false;
        }

        $fileData = file_get_contents($filePath);
        $fileData = $this->processFileData($fileData);
        return $this->loadString($fileData, $this->_elementClass);
    }

The End!