diff --git a/core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/CompositeConstraintBase.php b/core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/CompositeConstraintBase.php
new file mode 100644
index 0000000..9c78572
--- /dev/null
+++ b/core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/CompositeConstraintBase.php
@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintBase.
+ */
+
+namespace Drupal\Core\Entity\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Provides a base class for constraints validating multiple fields.
+ *
+ * The constraint must be defined on entity-level; i.e., added to the entity
+ * type. See ... @todo. fix this.
+ *
+ * With that the $values in CompositeConstraintValidatorBase::doValidate() will
+ * return an array keyed with 'name', 'uid' and 'entity', with 'entity' being
+ * the actual full entity.
+ */
+abstract class CompositeConstraintBase extends Constraint {
+
+  /**
+   * An array of entity fields which should be passed to the validator.
+   *
+   * @return string[]
+   *   An array of field names.
+   */
+  abstract public function coversFields();
+
+}
diff --git a/core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/CompositeConstraintValidatorBase.php b/core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/CompositeConstraintValidatorBase.php
new file mode 100644
index 0000000..70a0777
--- /dev/null
+++ b/core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/CompositeConstraintValidatorBase.php
@@ -0,0 +1,63 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintValidatorBase.
+ */
+
+namespace Drupal\Core\Entity\Plugin\Validation\Constraint;
+
+use Drupal\Core\Entity\FieldableEntityInterface;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+/**
+ * Base class for validators of the CompositeConstraintBase.
+ *
+ * @see \Drupal\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintBase
+ */
+abstract class CompositeConstraintValidatorBase extends ConstraintValidator {
+
+  /**
+   * The entity currently being validated.
+   *
+   * For validating field values, the values passed to doValidate() should be
+   * used instead of directly fetching the values from the entity objects.
+   *
+   * @var \Drupal\Core\Entity\FieldableEntityInterface|null
+   */
+  protected $entity;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($value, Constraint $constraint) {
+    /** @var \Drupal\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintBase $constraint */
+    if (!isset($value)) {
+      return;
+    }
+
+    // @todo: Throw exception if $value is not an entity; i.e. the constraint
+    // has been defined on the wrong level.
+    $this->entity = $value->getEntity();
+    $field_names = $constraint->coversFields();
+
+    $values = [];
+    foreach ($field_names as $field_name) {
+      $values[$field_name] = $this->entity->get($field_name);
+    }
+    $this->doValidate($values, $constraint);
+  }
+
+  /**
+   * Does the actual validation of a composite validator.
+   *
+   * @param \Drupal\Core\Field\FieldItemListInterface[] $values
+   *   The field values which are validated. Keys are field names and values
+   *   field item lists.
+   * @param \Symfony\Component\Validator\Constraint $constraint
+   *   The constraint for the validation.
+   */
+  abstract protected function doValidate(array $values, Constraint $constraint);
+
+}
diff --git a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CompositeConstraintBase.php b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CompositeConstraintBase.php
deleted file mode 100644
index a2c3b5d..0000000
--- a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CompositeConstraintBase.php
+++ /dev/null
@@ -1,43 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintBase.
- */
-
-namespace Drupal\Core\Validation\Plugin\Validation\Constraint;
-
-use Symfony\Component\Validator\Constraint;
-
-/**
- * Provides a constraint which validates multiple fields.
- *
- * You can configure the fields you need in your validator, by using
- * @code
- *   ->addConstraint('CommentName', ['fields' => ['name', 'uid', 'entity']]);
- * @encode
- * on entities.
- *
- * With that the $values in CompositeConstraintValidatorBase::doValidate() will
- * return an array keyed with 'name', 'uid' and 'entity', with 'entity' being
- * the actual full entity.
- */
-abstract class CompositeConstraintBase extends Constraint {
-
-  /**
-   * An array of entity fields which should be passed to the validator.
-   *
-   * @return string[]
-   */
-  protected $fields = [];
-
-  /**
-   * The composited fields.
-   *
-   * @return array
-   */
-  public function getFields() {
-    return $this->fields;
-  }
-
-}
diff --git a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CompositeConstraintValidatorBase.php b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CompositeConstraintValidatorBase.php
deleted file mode 100644
index ce3ec42..0000000
--- a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CompositeConstraintValidatorBase.php
+++ /dev/null
@@ -1,66 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintValidatorBase.
- */
-
-namespace Drupal\Core\Validation\Plugin\Validation\Constraint;
-
-use Symfony\Component\Validator\Constraint;
-use Symfony\Component\Validator\ConstraintValidator;
-
-/**
- * Base class for validators of the CompositeConstraintBase.
- *
- * @see \Drupal\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintBase
- */
-abstract class CompositeConstraintValidatorBase extends ConstraintValidator {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function validate($value, Constraint $constraint) {
-    if (!isset($value)) {
-      return;
-    }
-
-    /** @var \Drupal\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintBase $constraint */
-
-    $entity = $value->getEntity();
-    $fields = $constraint->getFields();
-
-    $values = [];
-    foreach ($fields as $field) {
-      if ($field === 'entity') {
-        $values['entity'] = $entity;
-        continue;
-      }
-
-      $split = explode('.', $field);
-      if (count($split) == 2) {
-        list($field, $property) = $split;
-      }
-      else {
-        $field = $split[0];
-        $property = $entity->{$field}->first()->mainPropertyName();
-      }
-
-      $values[$field] = $entity->{$field}->first()->{$property};
-    }
-
-    $this->doValidate($values, $constraint);
-  }
-
-  /**
-   * Does the actual validation of a composite validator.
-   *
-   * @param array $values
-   *   The available values, as configured in the constraint.
-   *
-   * @param \Symfony\Component\Validator\Constraint $constraint
-   *   The constraint for the validation.
-   */
-  abstract protected function doValidate(array $values, Constraint $constraint);
-
-}
diff --git a/core/modules/comment/src/Entity/Comment.php b/core/modules/comment/src/Entity/Comment.php
index 3c30c79..d6b8452 100644
--- a/core/modules/comment/src/Entity/Comment.php
+++ b/core/modules/comment/src/Entity/Comment.php
@@ -256,7 +256,7 @@ public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
       ->setTranslatable(TRUE)
       ->setSetting('max_length', 60)
       ->setDefaultValue('')
-      ->addConstraint('CommentName', ['fields' => ['name', 'uid', 'entity']]);
+      ->addConstraint('CommentName');
 
     $fields['mail'] = BaseFieldDefinition::create('email')
       ->setLabel(t('Email'))
diff --git a/core/modules/comment/src/Plugin/Validation/Constraint/CommentNameConstraint.php b/core/modules/comment/src/Plugin/Validation/Constraint/CommentNameConstraint.php
index ec3ef1b..15611e1 100644
--- a/core/modules/comment/src/Plugin/Validation/Constraint/CommentNameConstraint.php
+++ b/core/modules/comment/src/Plugin/Validation/Constraint/CommentNameConstraint.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\comment\Plugin\Validation\Constraint;
 
-use Drupal\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintBase;
+use Drupal\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintBase;
 
 /**
  * Supports validating comment author names.
@@ -40,4 +40,11 @@ class CommentNameConstraint extends CompositeConstraintBase {
    */
   public $messageMatch = 'The specified author name does not match the comment author.';
 
+  /**
+   * {@inheritdoc}
+   */
+  public function coversFields() {
+    return ['name', 'uid'];
+  }
+
 }
diff --git a/core/modules/comment/src/Plugin/Validation/Constraint/CommentNameConstraintValidator.php b/core/modules/comment/src/Plugin/Validation/Constraint/CommentNameConstraintValidator.php
index a1cc844..e13953c 100644
--- a/core/modules/comment/src/Plugin/Validation/Constraint/CommentNameConstraintValidator.php
+++ b/core/modules/comment/src/Plugin/Validation/Constraint/CommentNameConstraintValidator.php
@@ -8,7 +8,7 @@
 namespace Drupal\comment\Plugin\Validation\Constraint;
 
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
-use Drupal\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintValidatorBase;
+use Drupal\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintValidatorBase;
 use Drupal\user\UserStorageInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Drupal\comment\CommentInterface;
@@ -47,10 +47,8 @@ public static function create(ContainerInterface $container) {
    * {@inheritdoc}
    */
   protected function doValidate(array $values, Constraint $constraint) {
-    $author_name = $values['name'];
-    $owner_id = (int) $values['uid'];
-
-    $comment = $values['entity'];
+    $author_name = $values['name']->value;
+    $owner_id = (int) $values['uid']->target_id;
 
     // Do not allow unauthenticated comment authors to use a name that is
     // taken by a registered user.
@@ -70,7 +68,7 @@ protected function doValidate(array $values, Constraint $constraint) {
 
     // Anonymous account might be required - depending on field settings.
     if ($owner_id === 0 && empty($author_name) &&
-      $this->getAnonymousContactDetailsSetting($comment) === COMMENT_ANONYMOUS_MUST_CONTACT) {
+      $this->getAnonymousContactDetailsSetting($this->entity) === COMMENT_ANONYMOUS_MUST_CONTACT) {
       $this->context->addViolation($constraint->messageRequired);
     }
   }
diff --git a/core/tests/Drupal/Tests/Core/Entity/Plugin/Validation/Constraint/CompositeConstraintValidatorBaseTest.php b/core/tests/Drupal/Tests/Core/Entity/Plugin/Validation/Constraint/CompositeConstraintValidatorBaseTest.php
new file mode 100644
index 0000000..7ef0cbc
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Entity/Plugin/Validation/Constraint/CompositeConstraintValidatorBaseTest.php
@@ -0,0 +1,116 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintValidatorBase.
+ */
+
+namespace Drupal\Tests\Core\Entity\Plugin\Validation\Constraint;
+
+use Drupal\Core\Entity\Plugin\DataType\EntityAdapter;
+use Drupal\Core\Field\Plugin\Field\FieldType\StringItem;
+use Drupal\Core\Field\FieldItemList;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintValidatorBase
+ * @group Validation
+ */
+class CompositeConstraintValidatorBaseTest extends UnitTestCase {
+
+  /**
+   * Tests validation.
+   */
+  public function testValidate() {
+    $constraint = new TestConstraint();
+    $validator = new TestConstraintValidator();
+    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    $context->expects($this->never())
+      ->method('addViolation');
+    $validator->initialize($context);
+
+    $items = $this->getMockedFieldItems('example value');
+    $validator->validate($items, $constraint);
+
+    $validator = new TestConstraintValidator();
+    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    $context->expects($this->once())
+      ->method('addViolation');
+    $validator->initialize($context);
+    $items = $this->getMockedFieldItems('invalid value');
+    $validator->validate($items, $constraint);
+  }
+
+  /**
+   * Get Mocked field items for the given value.
+   *
+   * @param string $value
+   *   The value to set.
+   *
+   * @return \Drupal\Core\Field\FieldItemList
+   */
+  protected function getMockedFieldItems($value) {
+    $entity = $this->getMock('Drupal\Core\Entity\ContentEntityInterface');
+
+    $definition = $this->getMock('\Drupal\Core\TypedData\ComplexDataDefinitionInterface');
+    $definition->expects($this->any())
+      ->method('getPropertyDefinitions')
+      ->willReturn([]);
+    $item = new StringItem($definition);
+    $item->value = $value;
+
+    $items = $this->getMock('\Drupal\Core\Field\FieldItemListInterface');
+    $items->expects($this->any())->method('first')->willReturn($item);
+
+    $entity->expects($this->once())
+      ->method('get')
+      ->with('normal_field')
+      ->willReturn($items);
+
+    $entity_adapter = EntityAdapter::createFromEntity($entity);
+    $definition = $this->getMock('\Drupal\Core\TypedData\DataDefinitionInterface');
+    return new FieldItemList($definition, NULL, $entity_adapter);
+  }
+
+}
+
+namespace Drupal\Tests\Core\Entity\Plugin\Validation\Constraint;
+
+use Drupal\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintBase;
+use Drupal\Core\Entity\Plugin\Validation\Constraint\CompositeConstraintValidatorBase;
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Test composite constraint.
+ */
+class TestConstraint extends CompositeConstraintBase {
+
+  public $message = "invalid";
+
+  /**
+   * An array of entity fields which should be passed to the validator.
+   *
+   * @return string[]
+   *   An array of field names.
+   */
+  public function coversFields() {
+    return ['normal_field'];
+  }
+}
+
+/**
+ * Test composite constraint validator.
+ */
+class TestConstraintValidator extends CompositeConstraintValidatorBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function doValidate(array $values, Constraint $constraint) {
+    if (!isset($values['normal_field']) || $values['normal_field']->first()->value !== 'example value') {
+      $this->context->addViolation($constraint->message);
+    }
+
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/CompositeConstraintValidatorBaseTest.php b/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/CompositeConstraintValidatorBaseTest.php
deleted file mode 100644
index beebdfa..0000000
--- a/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/CompositeConstraintValidatorBaseTest.php
+++ /dev/null
@@ -1,83 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Tests\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintValidatorBase.
- */
-
-namespace Drupal\Tests\Core\Validation\Plugin\Validation\Constraint;
-
-use Drupal\Core\Entity\ContentEntityInterface;
-use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Entity\Plugin\DataType\EntityAdapter;
-use Drupal\Core\Field\FieldItemList;
-use Drupal\Core\Field\Plugin\Field\FieldType\StringItem;
-use Drupal\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintBase;
-use Drupal\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintValidatorBase;
-use Drupal\Tests\UnitTestCase;
-use Symfony\Component\Validator\Constraint;
-use Symfony\Component\Validator\ExecutionContext;
-
-/**
- * @coversDefaultClass \Drupal\Core\Validation\Plugin\Validation\Constraint\CompositeConstraintValidatorBase
- * @group Validation
- */
-class CompositeConstraintValidatorBaseTest extends UnitTestCase {
-
-  public function testValidate() {
-    $constaint = new TestConstraint(['fields' => ['normal_field', 'entity']]);
-    $validator = new TestConstraintValidator();
-
-    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
-    $context->expects($this->never())
-      ->method('addViolation');
-
-    $validator->initialize($context);
-
-    $entity = $this->getMock('Drupal\Core\Entity\ContentEntityInterface');
-
-    $definition = $this->getMock('\Drupal\Core\TypedData\ComplexDataDefinitionInterface');
-    $definition->expects($this->any())
-      ->method('getPropertyDefinitions')
-      ->willReturn([]);
-    $item = new StringItem($definition);
-    $item->value = 'example value';
-
-    $items = $this->getMock('\Drupal\Core\Field\FieldItemListInterface');
-    $items->expects($this->any())
-      ->method('first')
-      ->willReturn($item);
-    $entity->normal_field = $items;
-
-    $entity_adapter = EntityAdapter::createFromEntity($entity);
-    $definition = $this->getMock('\Drupal\Core\TypedData\DataDefinitionInterface');
-    $items = new FieldItemList($definition, NULL, $entity_adapter);
-
-    $validator->validate($items, $constaint);
-  }
-
-}
-
-class TestConstraint extends CompositeConstraintBase {
-
-  public $message = "invalid";
-
-}
-
-class TestConstraintValidator extends CompositeConstraintValidatorBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function doValidate(array $values, Constraint $constraint) {
-    if (!isset($values['normal_field']) || $values['normal_field'] !== 'example value') {
-      $this->context->addViolation($constraint->message);
-    }
-
-    if (!isset($values['entity']) || !($values['entity'] instanceof ContentEntityInterface)) {
-      $this->context->addViolation($constraint->message);
-    }
-
-  }
-
-}