1. Create a MessageStorage class in the module's src directory. This class will extend the default \Drupal\Core\Entity\Sql\SqlContentEntityStorage class:

<?php 
 
namespace Drupal\mymodule; 
 
use Drupal\Core\Entity\Sql\SqlContentEntityStorage; 
 
/** 
 * Defines the entity storage for messages. 
 */ 
class MessageStorage extends SqlContentEntityStorage { 
 
} 

By extending the default storage class for our entity type, we can simply add new methods that are relevant to our requirements rather than implementing the extra business logic.

2. Create a loadMultipleByType method; using this method, we will provide a simple way to load all messages of a specific bundle:

  /** 
   * Load multiple messages by bundle type. 
   * 
   * @param string $message_type 
   *   The message type. 
   * 
   * @return array|\Drupal\Core\Entity\EntityInterface[] 
   *   An array of loaded message entities. 
   */ 
  public function loadMultipleByType($message_type) { 
    return $this->loadByProperties([ 
      'type' => $message_type, 
    ]); 
  } 
  

We pass the type property so that we can query it based on the message bundle and return all matching message entities.

3. Update the entity's annotation block to have the new storage handler defined:

handlers = { 
  "list_builder" = "Drupal\mymodule\MessageListBuilder", 
  "access" = "\Drupal\entity\EntityAccessControlHandler", 
  "permission_provider" = "\Drupal\entity\EntityPermissionProvider", 
  "storage" = "Drupal\mymodule\MessageStorage", 
  "form" = { 
    "default" = "Drupal\Core\Entity\EntityForm", 
    "add" = "Drupal\Core\Entity\EntityForm", 
    "edit" = "Drupal\Core\Entity\EntityForm", 
    "delete" = "Drupal\Core\Entity\EntityDeleteForm" 
  }, 
  "route_provider" = { 
    "html" = "Drupal\Core\Entity\Routing\DefaultHtmlRouteProvider", 
  }, 
}, 

4. You can now programmatically interact with your message entities using the following code:

// Get the entity type manager from the container. 
\Drupal::entityTypeManager() 
 
// Access the storage handler. 
->getStorage('message') 
 
// Invoke the new method on custom storage class. 
->loadMultipleByType('message');