Create collection in Magento 2

Create Model File Allnews.php

Rsgitech\News\Model\Allnews.php

<?php
namespace Rsgitech\News\Model;

use Magento\Framework\Model\AbstractModel;

class Allnews extends AbstractModel
{
	const CACHE_TAG = 'rsgitech_news';
	
	//Unique identifier for use within caching
	protected $_cacheTag = self::CACHE_TAG;
	
	protected function _construct()
    {
        $this->_init('Rsgitech\News\Model\ResourceModel\Allnews');
    }
	
    public function getIdentities()
    {
        return [self::CACHE_TAG . '_' . $this->getId()];
    }

    public function getDefaultValues()
    {
        $values = [];
        return $values;
    }
}
?>

Copy

Create Resource Model

Rsgitech\News\Model\ResourceModel\Allnews.php

Define table in resource model

<?php
namespace Rsgitech\News\Model\ResourceModel;

use Magento\Framework\Model\AbstractModel;

class Allnews extends \Magento\Framework\Model\ResourceModel\Db\AbstractDb
{
	public function __construct(
        \Magento\Framework\Model\ResourceModel\Db\Context $context
    ) {
        parent::__construct($context);
    }
	
	/**
     * Define main table
     */
	protected function _construct()
	{
		$this->_init('rsgitech_news', 'news_id');
	}
}
?>

Copy

Create Collection

Rsgitech\News\Model\ResourceModel\Allnews\Collection.php

Define model and resource model

<?php
namespace Rsgitech\News\Model\ResourceModel\Allnews;

use Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection;

class Collection extends AbstractCollection
{
    protected $_idFieldName = 'news_id';
	
	protected $_eventPrefix = 'news_allnews_collection';

    protected $_eventObject = 'allnews_collection';
	
	/**
     * Define model & resource model
     */
	protected function _construct()
	{
		$this->_init('Rsgitech\News\Model\Allnews', 'Rsgitech\News\Model\ResourceModel\Allnews');
	}
}
?>

Copy

View Collection on Controller Action

Rsgitech\News\Controller\Adminhtml\AllNews\Index.php

View collection on controller

<?php
namespace Rsgitech\News\Controller\Adminhtml\AllNews;

class Index extends \Magento\Backend\App\Action
{
	protected $allNewsFactory;
	
	protected $resultPageFactory;
	
	public function __construct(
		\Magento\Backend\App\Action\Context $context,
		\Magento\Framework\View\Result\PageFactory $resultPageFactory,
		\Rsgitech\News\Model\AllnewsFactory $allNewsFactory
	) {
		parent::__construct($context);
		$this->resultPageFactory = $resultPageFactory;
		$this->allNewsFactory = $allNewsFactory;
	}

	public function execute()
	{
		$allnews = $this->allNewsFactory->create();
		$newsCollection = $allnews->getCollection();
		
		echo '<pre>';print_r($newsCollection->getData());
		
		//$resultPage = $this->resultPageFactory->create();
		//return $resultPage
	}
}
?>

Copy

Then run below commands

php bin/magento setup:upgrade
php bin/magetno setup:static-content:deploy
php bin/magento cache:flush

Copy