Drupal所能够理解的资源

Drupal能够识别哪些资源类型？

profile，不知道怎么翻译，应该是指安装类型，固定地存放于profiles目录下。

module，模块，可以存在于多个目录下：modules、profiles/{profile}/modules、sites/all/modules、sites/{$site}/modules。
theme，主题，可以存在于多个目录下：themes、profiles/{profile}/themes、sites/all/themes、sites/{$site}/themes。
theme_engine，主题引擎，可以存在于多个目录下：themes/engines、profiles/{profile}/themes/engines、sites/all/themes/engines、sites/{$site}/themes/engines。

Drupal识别的这些资源都可以注册到系统表system里面，用资源主文件作为key，用type字段表示资源类型。

Drupal如何找到指定的资源？

Drupal使用drupal_get_filename()和drupal_system_listing()两个函数配合来寻找指定的资源。

最先进入的是drupal_get_filename()函数，该函数以资源类型和资源名称作为传入参数：

function drupal_get_filename($type, $name, $filename = NULL)  { ... ... }

profile资源固定地存放在profiles目录下，这是在代码里面固定写死了的：

if ($type == 'profile') {
    $profile_filename = "profiles/$name/$name.profile";
    $files[$type][$name] = file_exists($profile_filename) ? $profile_filename : FALSE;
  }

然后在系统表system中搜索对应的资源类型和名称是否有存在。若存在，代表该资源已经安装过，直接返回其key就是资源主文件。

if (function_exists('db_query')) {
  $file = db_query("SELECT filename FROM {system} WHERE name = :name AND type = :type", array(':name' => $name, ':type' => $type))->fetchField();
  if (file_exists(DRUPAL_ROOT . '/' . $file)) {
    $files[$type][$name] = $file;
  }
}

在system表找不到对应的资源，Drupal就直接去检查对应的目录是否存在。Drupal规定了每种资源的目录和主文件命名规则：

$dir = $type . 's';
if ($type == 'theme_engine') {
  $dir = 'themes/engines';
  $extension = 'engine';
}
elseif ($type == 'theme') {
  $extension = 'info';
}
else {
  $extension = $type;
}

资源目录命名规则是以资源类型加上s后缀，theme_engine例外，theme_engine目录是themes/engines。
资源主文件命名规则是资源名称加上资源类型后缀。theme和theme_engine的后缀例外，theme后缀是info，theme_engine后缀是engine。

每种资源都有多个目录可以存放，Drupal使用drupal_system_listing()函数定义其搜索顺序。

function drupal_system_listing($mask, $directory, $key = 'name', $min_depth = 1) {
  $config = conf_path();

  $searchdir = array($directory);
  $files = array();

  // The 'profiles' directory contains pristine collections of modules and
  // themes as organized by a distribution. It is pristine in the same way
  // that /modules is pristine for core; users should avoid changing anything
  // there in favor of sites/all or sites/<domain> directories.
  $profiles = array();
  $profile = drupal_get_profile();

  // In case both profile directories contain the same extension, the actual
  // profile always has precedence.
  $profiles[] = $profile;
  foreach ($profiles as $profile) {
    if (file_exists("profiles/$profile/$directory")) {
      $searchdir[] = "profiles/$profile/$directory";
    }
  }

  // Always search sites/all/* as well as the global directories.
  $searchdir[] = 'sites/all/' . $directory;

  if (file_exists("$config/$directory")) {
    $searchdir[] = "$config/$directory";
  }

  // Get current list of items.
  if (!function_exists('file_scan_directory')) {
    require_once DRUPAL_ROOT . '/includes/file.inc';
  }
  foreach ($searchdir as $dir) {
    $files_to_add = file_scan_directory($dir, $mask, array('key' => $key, 'min_depth' => $min_depth));

    // Duplicate files found in later search directories take precedence over
    // earlier ones, so we want them to overwrite keys in our resulting
    // $files array.
    // The exception to this is if the later file is from a module or theme not
    // compatible with Drupal core. This may occur during upgrades of Drupal
    // core when new modules exist in core while older contrib modules with the
    // same name exist in a directory such as sites/all/modules/.
    foreach (array_intersect_key($files_to_add, $files) as $file_key => $file) {
      // If it has no info file, then we just behave liberally and accept the
      // new resource on the list for merging.
      if (file_exists($info_file = dirname($file->uri) . '/' . $file->name . '.info')) {
        // Get the .info file for the module or theme this file belongs to.
        $info = drupal_parse_info_file($info_file);

        // If the module or theme is incompatible with Drupal core, remove it
        // from the array for the current search directory, so it is not
        // overwritten when merged with the $files array.
        if (isset($info['core']) && $info['core'] != DRUPAL_CORE_COMPATIBILITY) {
          unset($files_to_add[$file_key]);
        }
      }
    }
    $files = array_merge($files, $files_to_add);
  }

  return $files;
}

这里举一个搜索hello模块的例子来说明搜索的过程。根据上面的资源命名规则可以知道，模块目录的命名规则是资源类型加s后缀，也就是modules。然后模块主文件的命名规则是资源名称加上资源类型后缀，也就是hello.module。好了，现在我们要找的就是modules/hello/hello.module文件。那到哪里去找这个文件呢？drupal_system_listing()会依次搜索以下四个位置：

• modules/hello/hello.module
• profiles/drupal_get_profile()/modules/hello/hello.module
• sites/all/modules/hello/hello.module
• sites/conf_path()/modules/hello/hello.module

找到了就OK，找不到就说明hello模块不存在。

Drupal如何载入指定资源？

Drupal用drupal_load()函数载入资源。首先用drupal_get_filename()得到资源主文件，然后简单的include_once就完了。

function drupal_load($type, $name) {
  static $files = array();

  if (isset($files[$type][$name])) {
    return TRUE;
  }

  $filename = drupal_get_filename($type, $name);

  if ($filename) {
    include_once DRUPAL_ROOT . '/' . $filename;
    $files[$type][$name] = TRUE;

    return TRUE;
  }

  return FALSE;
}