Php 如何在magento 2中使用mysql查询获取db表值。Magento 2是否使用sql查询？

我是新来的

CustomModule\Database\Controller\Page\Index.php

<?php
namespace CustomModule\Database\Controller\Page;
class Index extends \Magento\Framework\App\Action\Action
{
    protected $_pageFactory;

    public function __construct(
        \Magento\Framework\App\Action\Context $context,
        \Magento\Framework\View\Result\PageFactory $pageFactory)
    {
        $this->_pageFactory = $pageFactory;
        return parent::__construct($context);
    }

    public function execute()
    {
        return $this->_pageFactory->create();
    }
}

<?php

namespace CustomModule\Database\Block;

use Magento\Framework\View\Element\Template;

class Index extends Template
{
 
    /**
     * @var \Magento\Framework\App\ResourceConnection
     */
    public $resourceConnection;
 
    public function __construct(
        \Magento\Framework\App\Action\Context $context,
        \Magento\Framework\App\ResourceConnection $resourceConnection
    ) {
        $this->resourceConnection = $resourceConnection;
        parent::__construct($context);
    }
 
    /**
     * Get Table name using direct query
     */
    public function getTablename($tableName)
    {
        /* Create Connection */
        $connection  = $this->resourceConnection->getConnection();
        $tableName   = $connection->getTableName($tableName);
        return $tableName;
    }
}

显示错误

protected $_resource;

public function __construct(
    \Magento\Framework\App\ResourceConnection $resource
) {
    $this->_resource = $resource;
}

public function execute()
{
    // get connection
    $connection     = $this->_resource->getConnection();
    // table name
    $tableName = $this->_resource->getTableName('your table name');
    // Query
    $select_sql = "Select * FROM " . $tableName;
    // fetch result
    $results = $connection->fetchAll($select_sql);
    // print result
    print_r($results);
}

1个例外情况：
异常#0（Magento\Framework\Exception\RuntimeException）：创建对象时发生类型错误：CustomModule\Database\Block\Index
   /** @var \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory */
   private $productCollectionFactory;

   public function __construct(\Magento\Catalog\Model\ResourceModel\Product\CollectionFactory $productCollectionFactory) {
      $this->productCollectionFactory = $productCollectionFactory;
   }

异常#0（Magento\Framework\Exception\RuntimeException）：创建对象时发生类型错误：CustomModule\Database\Block\Index
   /** @var \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory */
   private $productCollectionFactory;

   public function __construct(\Magento\Catalog\Model\ResourceModel\Product\CollectionFactory $productCollectionFactory) {
      $this->productCollectionFactory = $productCollectionFactory;
   }

#1在[vendor\Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create（'CustomModule\Dat…'，array（'data'=>array（））调用[vendor\Magento\Framework\ObjectManager\ObjectManager.php:56]
#2在[vendor\Magento\Framework\View\Element\BlockFactory.php:46]调用Magento\Framework\ObjectManager\ObjectManager->create（'CustomModule\Dat…'，array（'data'=>array（）））
#3在[vendor\Magento\Framework\View\Element\BlockFactory->createBlock（'CustomModule\Dat…'，array（'data'=>array（））调用[vendor\Magento\Framework\View\Layout\Generator\Block.php:272]
#4在[vendor\Magento\Framework\View\Layout\Generator\Block.php:252]调用的Magento\Framework\View\Layout\Generator\Block->getBlockInstance（'CustomModule\Dat…'，array（'data'=>array（）
#5在[vendor\Magento\Framework\View\Layout\Generator\Block->createBlock（'CustomModule\Dat…'，'index'，array（'data'=>array（））调用的Magento\Framework\View\Layout\Generator\Block.php:229]
#在[vendor\Magento\Framework\View\Layout\Generator\Block]调用6 Magento\Framework\View\Layout\ScheduledStructure（&Magento\Framework\View\Layout\Block->generateBlock（&Magento\Framework\View\Layout\ScheduledStructure\000000000 6B3BC800000037A2237A2235D#，'index'），&Magento\Framework\Framework\View\Layout\Layout\dataer\Block.php:134]
#7在[vendor\Magento\Framework\View\Layout\Generator\Context]调用的Magento\Framework\View\Layout\Generator\Block->process（&Magento\Framework\View\View\Layout\Reader\Context\0000000006B33B33B0000000037A2235D；&Magento\Framework\View\Layout\GeneratorPool.php:81]
#在[vendor\Magento\Framework\View\Layout\GeneratorPool->process（&Magento\Framework\View\Layout\Reader\Context#000000000 6B33B33B0000000037A2235D#，&Magento\Framework\View\Layout\Generator\Context#000000000 6B38D0000000037A2235D#）处调用
#9在[vendor\Magento\Framework\intercept\Interceptor.php:58]处调用Magento\Framework\View\Layout->generateElements（）
#10在[vendor\Magento\Framework\View\Layout\Interceptor->\uuuuuuuuu callParent（'generateeelements'，array（））调用[vendor\Magento\Framework\intercepton\Interceptor.php:138]
#11在[vendor\Magento\Framework\View\Layout\Interceptor->Magento\Framework\intercepton\{closure}调用Magento\Framework\intercepton\Interceptor.php:153]
#12在[generated\code\Magento\Framework\View\Layout\Interceptor.]调用的Magento\Framework\View\Interceptor->\uuuuuu调用插件（'generateElements'，array（），array（array（'Layout-model-cac…'，'core-session-dep…，'customer session…'，'catalog session-…'，'persistent session…'，'checkout session…'，'tax session depe…）））
#13在[vendor\Magento\Framework\View\Layout\Interceptor->generateElements（）调用[vendor\Magento\Framework\View\Layout\Builder.php:129]
#14在[vendor\Magento\Framework\View\Layout\Builder.php:55]处调用Magento\Framework\View\Page\Builder->generateLayoutBlocks（）
#15 Magento\Framework\View\Page\Builder->generateLayoutBlocks（）在[vendor\Magento\Framework\View\Layout\Builder.php:65]处调用
#16在[vendor\Magento\Framework\View\Layout\Builder->build]调用Magento\Framework\View\Page\Config.php:224]
#17在[vendor\Magento\Framework\View\Page\Config->build（）处调用Magento\Framework\View\Page\Config.php:237]
#18在[generated\code\Magento\Framework\View\Page\Config->publicBuild]调用Magento\Framework\View\Page\Config\Interceptor.php:37]
#19在[vendor\Magento\Framework\View\Page\Config\Interceptor->publicBuild]调用Magento\Framework\View\Result\Page.php:242]
#20在[vendor\Magento\Framework\View\Result\Page->render（&Magento\Framework\App\Response\Http\Interceptor\000000000 6B3BBDE0000000037A2235D）调用[vendor\Magento\Framework\View\Result\Layout.php:171]
#21在[vendor\Magento\Framework\Result\Layout->renderResult（&Magento\Framework\App\Response\Http\Interceptor#000000000 6B3BBDE0000000037A2235D#）调用[vendor\Magento\Framework\intercepton\Interceptor.php:58]
#22在[vendor\Magento\Framework\View\Result\Page\Interceptor->\uuuuuuuu callParent（'renderResult'，array（&Magento\Framework\App\Response\Http\Interceptor#000000000 6B3BBDE0000000037A2235D#））调用的Magento\Framework\intercepton\Interceptor.php:138]
#23在[vendor\Magento\Framework\View\Result\Page\Interceptor->Magento\Framework\intercepton\{closure}（&Magento\Framework\App\Response\Http\Interceptor#000000000 6B3BBDE0000000037A2235D#）调用[vendor\Magento\Framework\intercepton\Interceptor.php:153]
#24 Magento\Framework\View\Result\Page\Interceptor->\uuuuu调用插件（'renderResult'，数组（&Magento\Framework\App\Response\Http\Interceptor#000000000 6B3BBDE0000000037A2235D#），数组（数组（'Result-messages'，'Result-builtin-c..，'Result-varnish-c..））调用于[generated\code\Magento\Framework\View\Result\Page\Interceptor.php:130]
#25在[vendor\Magento\Framework\View\Result\Page\Interceptor->renderResult（&Magento\Framework\App\Response\Http\Interceptor\000000000 6B3BBDE0000000037A2235D）调用[vendor\Magento\Framework\App\Http.php:120]
#26在[generated\code\Magento\Framework\App\Http->launch]调用Magento\Framework\App\Http\Interceptor.php:24]
#27在[vendor\Magento\Framework\App\Http\Interceptor->launch]调用Magento\Framework\App\Bootstrap.php:261]
#28在[index.php:39]调用Magento\Framework\App\Bootstrap->run（&Magento\Framework\App\Http\Interceptor#000000000 6B3BBD7000000037A2235D）

您可以使用以下代码通过MySQL查询从数据库表中获取数据：

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简单的回答是：你没有。
Magento 2为您提供了访问数据库资源的集合和工厂，而不需要您进行写操作

   /** @var \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory */
   private $productCollectionFactory;

   public function __construct(\Magento\Catalog\Model\ResourceModel\Product\CollectionFactory $productCollectionFactory) {
      $this->productCollectionFactory = $productCollectionFactory;
   }