hook_views_data() for entities replaced with EntityViewsDataInterface

hook_views_data() for entity data was replaced with a new Views entity data object, since entity schemas are now generated automatically based on the entity itself. hook_views_data() is still used for exposing other database tables to views.)

Drupal 7

/**
  * Implements hook_views_data().
  *
  * Normally found in module.views.inc.
  */
function mymodule_views_data() {
  // define views columns/intergration.
}

Drupal 8

In your entity annotation define an entry for views like so

*     "views_data" = "Drupal\comment\CommentViewsData",

For example from comment module.

/**
 * Defines the comment entity class.
 *
 * @ContentEntityType(
 *   id = "comment",
 *   label = @Translation("Comment"),
      ....
 *   handlers = {
 *     "views_data" = "Drupal\comment\CommentViewsData",
 *   },

Then define your Views data integration:

/**
* @file
* Contains \Drupal\comment\CommentViewsData.
*/

namespace Drupal\comment;

use Drupal\views\EntityViewsDataInterface;

/**
 * Provides views data for the comment entity type.
 */
class CommentViewsData implements EntityViewsDataInterface {

  /**
   * {@inheritdoc}
   */
  public function getViewsData() {
    $data = array();
    // Define your fields etc.
    return $data;
  }
}