Magento 2: How to query data in Observer?

Question

As title said, i want to query the data from custom table in Observer file. How to do it?

Answer 1

1/You can put these codes in your observer. Here is an example for output all data in theme table :

    $themeId=3;

    $this->_resources = \Magento\Framework\App\ObjectManager::getInstance()
        ->get('Magento\Framework\App\ResourceConnection');
    $connection= $this->_resources->getConnection();

    $select = $connection->select()
        ->from(
            ['o' =>  $this->_resources->getTableName('theme')]
        );

    $result = $connection->fetchAll ($select);
    var_dump($result);

You can change the query to insert or delete, update according to zend framework.

The result is :

2/The another way is reusing Magento Object Manager:

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();

    $productCollection = $objectManager->create('Magento\Catalog\Model\ResourceModel\Product\CollectionFactory');//insert your custom resource model

    $collection = $productCollection->create()
        ->addAttributeToSelect('*')
        ->load();

    foreach ($collection as $product){
        echo 'Name  =  '.$product->getName().'<br>';
    }

Answer 2

Best practice Magento 2 : Use dependency injection

Don't load custom Model or ResourceModel with Object Manager directly like that :

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$resourceModel = $objectManager->create('Vendor\Module\Model\ResourceModel\Custom');
$resourceModel->loadBySomething('example');

But you should load it like this :

<?php

namespace Vendor\Module\Observer;

use Vendor\Module\Model\ResourceModel\Custom;
use Magento\Framework\Event\ObserverInterface;

class myObserver implements ObserverInterface
{
    protected $resourceModel;

    public function __construct(
        Custom $resourceModel
    ){
        $this->resourceModel = $resourceModel
    }

    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        $event = $observer->getEvent();

        $this->resourceModel->loadBySomething('example');
    }
}