作者：老葛，北京亚艾元软件有限责任公司，http://www.yaiyuan.com
我们来看阶段2，也就是数据库阶段，对应的代码：
case DRUPAL_BOOTSTRAP_DATABASE:
_drupal_bootstrap_database();
break;
Drupal将这个阶段要做的工作，委托给了__drupal_bootstrap_database函数。这个函数就位于bootstrap.inc文件中，我们通过文本查找，很快就找到了这个函数的定义：
/**
* Initializes the database system and registers autoload functions.
*/
function _drupal_bootstrap_database() {
// Redirect the user to the installation script if Drupal has not been
// installed yet (i.e., if no $databases array has been defined in the
// settings.php file) and we are not already installing.
if (empty($GLOBALS['databases']) && !drupal_installation_attempted()) {
include_once DRUPAL_ROOT . '/includes/install.inc';
install_goto('install.php');
}
// The user agent header is used to pass a database prefix in the request when
// running tests. However, for security reasons, it is imperative that we
// validate we ourselves made the request.
if ($test_prefix = drupal_valid_test_ua()) {
// Set the test run id for use in other parts of Drupal.
$test_info = &$GLOBALS['drupal_test_info'];
$test_info['test_run_id'] = $test_prefix;
$test_info['in_child_site'] = TRUE;
foreach ($GLOBALS['databases']['default'] as &$value) {
// Extract the current default database prefix.
if (!isset($value['prefix'])) {
$current_prefix = '';
}
elseif (is_array($value['prefix'])) {
$current_prefix = $value['prefix']['default'];
}
else {
$current_prefix = $value['prefix'];
}
// Remove the current database prefix and replace it by our own.
$value['prefix'] = array(
'default' => $current_prefix . $test_prefix,
);
}
}
// Initialize the database system. Note that the connection
// won't be initialized until it is actually requested.
require_once DRUPAL_ROOT . '/includes/database/database.inc';
// Register autoload functions so that we can access classes and interfaces.
// The database autoload routine comes first so that we can load the database
// system without hitting the database. That is especially important during
// the install or upgrade process.
spl_autoload_register('drupal_autoload_class');
spl_autoload_register('drupal_autoload_interface');
}
这个函数代码里面的第一部分，当数据库为空，当前尚未安装Drupal的时候，此时做了重定向，重定向到了install.php页面。
if (empty($GLOBALS['databases']) && !drupal_installation_attempted()) {
include_once DRUPAL_ROOT . '/includes/install.inc';
install_goto('install.php');
}
这个函数代码里面的第二部分，表示如果当前为单元测试环境下，要做的工作，我们这里不是单元测试环境，所以不需要考虑这段代码的含义：
if ($test_prefix = drupal_valid_test_ua()) {
…
}
再往下，是加载includes/database/database.inc文件，这样就可以建立数据库连接了。最后是自动加载（缓加载）。
spl_autoload_register('drupal_autoload_class');
spl_autoload_register('drupal_autoload_interface');
我们这里看到，Drupal7只支持类、接口的缓加载，不支持函数的缓加载。我第一集里面讲过这个问题，今天看到的是对应的代码部分。
