如何连接两张桌子？

Question

我一直在关注本教程的Drupal模块开发。讨论了模块开发中的数据库查询连接。本教程是为Drupal 8编写的，我正在使用Drupal 9。

然后我做了这个(看看联接部分)：

  protected function load () {
    $select = Database::getConnection()->select('rsvplist', 'r');
    $select.join('users_field_data', 'u', 'r.uid = u.uid');
    $select->join('node_field_data', 'n', 'r.nid = n.nid');
    $select->addField('u', 'name');
    $select->addField('n', 'title');
    $select->addField('r', 'mail');
    $entries = $select->execute()->fetchAll(\PDO::FETCH_ASSOC);
    return $entries;
  }

但是得到这个错误：

warning: join() expects at most 2 parameters, 3 given in Drupal\rsvplist\Controller\ReportController->load() (line 24 of /var/www/htdocs/drupal-modules/modules/custom/rsvplist/src/Controller/ReportController.php)
#0 /var/www/htdocs/drupal-modules/core/includes/bootstrap.inc(305): _drupal_error_handler_real(2, 'join() expects ...', '/var/www/htdocs...', 24)
#1 [internal function]: _drupal_error_handler(2, 'join() expects ...', '/var/www/htdocs...', 24, Array)
#2 /var/www/htdocs/drupal-modules/modules/custom/rsvplist/src/Controller/ReportController.php(24): join('users_field_dat...', 'u', 'r.uid = u.uid')
#3 /var/www/htdocs/drupal-modules/modules/custom/rsvplist/src/Controller/ReportController.php(52): Drupal\rsvplist\Controller\ReportController->load()
#4 [internal function]: Drupal\rsvplist\Controller\ReportController->report()
#5 /var/www/htdocs/drupal-modules/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array)
#6 /var/www/htdocs/drupal-modules/core/lib/Drupal/Core/Render/Renderer.php(573): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#7 /var/www/htdocs/drupal-modules/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure))
#8 /var/www/htdocs/drupal-modules/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array)
#9 /var/www/htdocs/drupal-modules/vendor/symfony/http-kernel/HttpKernel.php(158): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#10 /var/www/htdocs/drupal-modules/vendor/symfony/http-kernel/HttpKernel.php(80): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#11 /var/www/htdocs/drupal-modules/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#12 /var/www/htdocs/drupal-modules/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#13 /var/www/htdocs/drupal-modules/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#14 /var/www/htdocs/drupal-modules/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#15 /var/www/htdocs/drupal-modules/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#16 /var/www/htdocs/drupal-modules/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#17 /var/www/htdocs/drupal-modules/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#18 /var/www/htdocs/drupal-modules/core/lib/Drupal/Core/DrupalKernel.php(706): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#19 /var/www/htdocs/drupal-modules/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#20 {main}

Drupal 9's加入不接受第三种说法：

'r.uid = u.uid'

A进行了一些研究，但我未能找到一个类似的例子，说明如何在Drupap 9文档和其他来源中以这种方式使用join。

如何将联接添加到Drupal 9中的查询中？

Answer 1

在PHP中：

• .是字符串连接操作符，而不是调用对象方法的操作符。
• join()是implode()函数的别名，它实际上需要2个参数，而不是3个

这意味着$select.join('users_field_data', 'u', 'r.uid = u.uid') ( PHP读取为$select . join('users_field_data', 'u', 'r.uid = u.uid'))是：

• 将$select中包含的值转换为字符串
• 将该字符串与implode()返回的字符串进行连接

implode()接受的参数在最新的PHP版本中已经更改，但是函数从未接受过三个参数，前两个参数从未是两个字符串。

这就解释了你所犯的错误。

在Drupal 9中，如果$select是实现SelectInterface的对象，则$select->join()是可用的方法。

public function join($table, $alias = NULL, $condition = NULL, $arguments = []) {
  return $this->addJoin('INNER', $table, $alias, $condition, $arguments);
}

而不是$select->join()，您可以调用$select->addJoin()。第一个方法不需要指定$select->addJoin()的第一个或最后一个参数，它是通常被调用的方法。

另外，与其在用于实体数据的数据库表上使用$select，不如使用从Drupal::entityQuery()返回的类。

Answer 2

解决方案：

在Drupal 9中，我需要替换joins以使其工作：

//$select.join('users_field_data', 'u', 'r.uid = u.uid');
$select->addJoin('inner','users_field_data','u','r.uid = u.uid');
//$select->join('node_field_data', 'n', 'r.nid = n.nid');
$select->addJoin('inner','node_field_data','n','r.nid = n.nid');