Merge pull request #8 from dawehner/base-field-trait

add a trait for really commmon base fields

src/EntityKeysFieldsTrait.php

+<?php
+
+/**
+ * @file
+ * Contains \Drupal\entity\EntityKeysFieldsTrait.
+ */
+
+namespace Drupal\entity;
+
+use Drupal\Core\Entity\ContentEntityTypeInterface;
+use Drupal\Core\Field\BaseFieldDefinition;
+
+/**
+ * Provides base fields for entity keys.
+ */
+trait EntityKeysFieldsTrait {
+
+  /**
+   * Returns the base field definitions for entity keys.
+   *
+   * @param \Drupal\Core\Entity\ContentEntityTypeInterface $entity_type
+   *   The entity type.
+   *
+   * @return \Drupal\Core\Field\BaseFieldDefinition[]
+   */
+  protected function entityKeysBaseFieldDefinitions(ContentEntityTypeInterface $entity_type) {
+    $fields = [];
+
+    if ($entity_type->hasKey('id')) {
+      $fields[$entity_type->getKey('id')] = BaseFieldDefinition::create('integer')
+        ->setLabel(t('ID'))
+        ->setReadOnly(TRUE)
+        ->setSetting('unsigned', TRUE);
+    }
+
+    if ($entity_type->hasKey('uuid')) {
+      $fields[$entity_type->getKey('uuid')] = BaseFieldDefinition::create('uuid')
+        ->setLabel(t('UUID'))
+        ->setReadOnly(TRUE);
+    }
+
+    if ($entity_type->hasKey('revision')) {
+      $fields[$entity_type->getKey('revision')] = BaseFieldDefinition::create('integer')
+        ->setLabel(t('Revision ID'))
+        ->setReadOnly(TRUE)
+        ->setSetting('unsigned', TRUE);
+    }
+
+    if ($entity_type->hasKey('langcode')) {
+      $fields[$entity_type->getKey('langcode')] = BaseFieldDefinition::create('language')
+        ->setLabel(t('Language'))
+        ->setTranslatable(TRUE)
+        ->setRevisionable(TRUE)
+        ->setDisplayOptions('view', [
+          'type' => 'hidden',
+        ])
+        ->setDisplayOptions('form', [
+          'type' => 'language_select',
+          'weight' => 2,
+        ]);
+    }
+
+    if ($bundle_entity_type_id = $entity_type->getBundleEntityType() && $entity_type->hasKey('bundle')) {
+      $bundle_key = $entity_type->getKey('bundle');
+      $fields[$bundle_key] = BaseFieldDefinition::create('entity_reference')
+        ->setLabel(t('Type'))
+        ->setSetting('target_type', $bundle_entity_type_id)
+        ->setReadOnly(TRUE);
+    }
+
+    return $fields;
+  }
+
+}