Unable to display database table values on frontend in magento 2.1.7

Question

I am trying to fetch table on frontend but getting this error

Fatal error: Class 'Crud\Crudatfrontend\Model\ResourceModel\Post' not found in D:\xampp\htdocs\newmag\vendor\magento\framework\ObjectManager\Factory\AbstractFactory.php on line 93

app/code/Crud/Crudatfrontend/
├── Block
│  └── index.php 
├── etc
│  └── module.xml
├── Model
│  ├── Post.php
│  ├── ResourceModel
│  │  ├── Post
│  │  │  └── Collection.php
│  │  └── Post.php
├── registration.php
├── Setup
│  └── InstallSchema.php
└── view
 └── frontend
 ├── layout
 │  └── crud_index_index.xml
 ├── templates
  └── index.phtml

Here is my code,

Block/Index.php

<?php
namespace Crud\Crudatfrontend\Block;
use Magento\Framework\App\Filesystem\DirectoryList;
class Index extends \Magento\Framework\View\Element\Template
{
 protected $_filesystem;
 public function __construct(
 \Magento\Framework\View\Element\Template\Context $context,
 \Crud\Crudatfrontend\Model\PostFactory $postFactory
 )
 { 
 parent::__construct($context);
 $this->_postFactory = $postFactory;
 } 
 public function getResult()
 {
 $post = $this->_postFactory->create();
 $collection = $post->getCollection();
 return $collection;
 }
}

Model/Post.php

<?php
namespace Crud\Crudatfrontend\Model;
class Post extends \Magento\Framework\Model\AbstractModel implements \Magento\Framework\DataObject\IdentityInterface
{
 protected function _construct()
 {
 $this->_init('Crud\Crudatfrontend\Model\ResourceModel\Post');
 }
 public function getIdentities()
 {
 return [self::CACHE_TAG . '_' . $this->getId()];
 }
 public function getDefaultValues()
 {
 $values = [];
 return $values;
 }
}

Model\ResourceModel\Post.php

<?php
namespace Crud\Crudatfrontend\Model\ResourceModel;
use \Magento\Framework\Model\ResourceModel\Db\AbstractDb;
class HelloWorld extends AbstractDb
{
 /**
 * Model initialization
 */
 protected function _construct()
 {
 $this->_init('Crud_Crudatfrontend', 'post_id');
 }
}

Model\ResourceModel\Post\collection.php

<?php
namespace Crud\Crudatfrontend\Model\ResourceModel\Post;
class Collection extends \Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection
{
 /**
 * Define resource model
 *
 * @return void
 */
 protected function _construct()
 {
 $this->_init('Crud\Crudatfrontend\Model\Post', 'Crud\Crudatfrontend\Model\ResourceModel\Post');
 }
}

Answer 1

Resources class name is wrong

class HelloWorld extends AbstractDb

it should be

class Post extends AbstractDb

Change it to Model\ResourceModel\Post.php