Content entity classes's interfaces should implement ContentEntityInterface

With the introduction of configuration entities, EntityInterface now has two child interfaces:

• ContentEntityInterface
• ConfigEntityInterface

Content entity classes should extend the Entity base class, and their entity type interface should implement ContentEntityInterface, for example:

namespace Drupal\comment\Plugin\Core\Entity;

use Drupal\comment\CommentInterface;
use Drupal\Core\Entity\Entity;

class Comment extends Entity implements CommentInterface {}

namespace Drupal\comment;

use Drupal\Core\Entity\ContentEntityInterface;

interface CommentInterface extends ContentEntityInterface {}

ContentEntityInterface does not currently define any methods on its own, but it can be extended to provide content-specific functionality.

The following core entity type interfaces extend ContentEntityInterface:

• FeedInterface (aggregator)
• ItemInterface (aggregator)
• CustomBlockInterface
• CommentInterface
• FileInterface
• MenuLinkInterface
• NodeInterface
• TermInterface

Since user accounts are not content, User extends entity without implementing the ContentEntityInterface:

namespace Drupal\user\Plugin\Core\Entity;

use Drupal\Core\Entity\Entity;
use Drupal\user\UserInterface;

class User extends Entity implements UserInterface {}

namespace Drupal\user;

use Drupal\Core\Entity\EntityInterface;

interface UserInterface extends EntityInterface {}

Note that configuration entity classes implement ConfigEntityInterface instead of ContentEntityInterface:

namespace Drupal\Core\Config\Entity;

use Drupal\Core\Entity\Entity;

abstract class ConfigEntityBase extends Entity implements ConfigEntityInterface {}

When defining a new entity class, decide whether the entity should be stored as content (like nodes), configuration (like node types), or neither (like users).