Entity - what it is ?

"Entities are the basic building blocks of Drupal's data model." - drupalize.me

"An entity would be one instance of a particular entity type such as a comment, taxonomy term or user profile or of a bundle such as a blog post, article or product."
- drupal.org

How many entities are here ?

Entity structure

Entity type

Bundle

Entity

Field

Entity group

Content 

• node
• user
• taxonomy_term
• file
• comment
• block_content
• menu_link_content
• contact_message
• ...

Configuration

• taxonomy_vocabulary
• node_type
• view
• comment_type
• contact_form
• block_content_type
• entity_form_display
• entity_view_display
• ...
  

Entity Types

• Fieldable, Revisionable, Translatable
• Dedicated class per type
• Entity type definition
• Field definitions

When to create a custom entity type ?

Bundles & Fields

• Base fields - on an entity type level
• Bundle fields - on a bundle level
• Fields can be shared accross Entity Type only
• Entity based swapable storage

Entity CRUD operations

Select

// Using static methods
$node = \Drupal::entityTypeManager()->getStorage('node')->load(22)

// When service container available
$service = \Drupal::service('entity_type.manager')->getStorage('node');
$node = $service->load(22);

// Loading multiple entities
$entity = \Drupal::entityTypeManager()->getStorage($entity_type)
  ->loadMultiple(array(22, 14, 8));

Create

// With procedural wrapper
$node = entity_create('node', array(
  'title' => 'Make blogs great again',
  'body' => 'This is where the body content goes...',
));

// Static method on the entity class
$node = Node::create(array('title' => 'A nice title'));

// The best way
$node = \Drupal::entityTypeManager()->getStorage('node')
  ->create(array('type' => 'page', 'title' => 'Story about me'));

Delete

// Delete a single entity.

$entity = \Drupal::entityTypeManager()->getStorage('node')->load(100);
$entity->delete();

// Delete multiple entities at once.

\Drupal::entityTypeManager()->getStorage($entity_type)
  ->delete(array($id1 => $entity1, $id2 => $entity2));

Getting Fields

// Accessing field values
$node = \Drupal::entityTypeManager()->getStorage("node")->load(22);

$body_text = $node->body->value; //
$body_text = $node->get('body')->value;
$body_array = $node->body->getValue();

// Methods are chainable
$second_tag = $node->field_tags[1]->entity->name->value;
$author_name = $node->uid->entity->name->value;

// Retrive referenced entities
$tags = $node->field_tags->referencedEntities();

Getting More Fields

// The most verbose way.
$string = $entity->get('image')->offsetGet(0)->get('alt')->getValue();

// A little bit of magic added by the Entity API.
$string = $entity->image[0]->alt;

// More magic - to fetch the first item
$string = $entity->image->alt;

Translations

// Get translation
$translation = $node->getTranslation('es');

// English version
print $node->title->value; 

// Spanish version
print $translation->title->value;

EntityQuery

Supports joins :)

// Get ids of your entities ...
$query = \Drupal::entityQuery('node')
    ->condition('status', 1)
    ->condition('changed', REQUEST_TIME, '<')
    ->condition('title', 'cat', 'CONTAINS')
    ->condition('field_tags.entity.name', 'cats');

$nids = $query->execute();

// ... Than load them
$node_storage = \Drupal::entityManager()->getStorage('node');
$nodes = $node_storage->loadMultiple($nids);

And aggregation :)

$query = Drupal::entityQueryAggregate('node')
  ->groupBy('type')
  ->aggregate('nid', 'COUNT');

$result = $query->execute();

// Result is array
#1 "article"	"158"
#2 "page"	"297"