Fix reading of nested errros

Testing the objects with `instanceof static` will not work for
different classes that extend `Entity`, as `static` will refer to
the extending class, ie the objects would get tested against the
class on which the `errors()` method is being called.

src/Datasource/EntityTrait.php

@@ -674,7 +674,7 @@ protected function _nestedErrors($field) {
 		while ($len) {
 			$part = array_shift($path);
 			$len = count($path);
-			if ($entity instanceof static) {
+			if ($entity instanceof self) {
 				$val = $entity->get($part);
 			} elseif (is_array($entity)) {
 				$val = isset($entity[$part]) ? $entity[$part] : false;
@@ -683,7 +683,7 @@ protected function _nestedErrors($field) {
 			if (
 				is_array($val) ||
 				$val instanceof Traversable ||
-				$val instanceof static
+				$val instanceof self
 			) {
 				$entity = $val;
 			} else {
@@ -705,12 +705,12 @@ protected function _nestedErrors($field) {
  * @return array
  */
 	protected function _readError($object, $path = null) {
-		if ($object instanceof static) {
+		if ($object instanceof self) {
 			return $object->errors($path);
 		}
 		if (is_array($object)) {
 			$array = array_map(function ($val) {
-				if ($val instanceof static) {
+				if ($val instanceof self) {
 					return $val->errors();
 				}
 			}, $object);

tests/TestCase/ORM/EntityTest.php

@@ -17,6 +17,9 @@
 use Cake\ORM\Entity;
 use Cake\TestSuite\TestCase;
 use Cake\Validation\Validator;
+use TestApp\Model\Entity\Author;
+use TestApp\Model\Entity\Owner;
+use TestApp\Model\Entity\User;
 
 /**
  * Entity test case.
@@ -822,30 +825,34 @@ public function testErrors() {
  * @return void
  */
 	public function testErrorsDeep() {
-		$entity2 = new Entity;
-		$entity3 = new Entity;
-		$entity = new Entity([
+		$user = new User();
+		$owner = new Owner();
+		$author = new Author([
 			'foo' => 'bar',
 			'thing' => 'baz',
-			'user' => $entity2,
-			'owner' => $entity3
+			'user' => $user,
+			'owner' => $owner
 		]);
-		$entity->errors('thing', ['this is a mistake']);
-		$entity2->errors(['a' => ['error1'], 'b' => ['error2']]);
-		$entity3->errors(['c' => ['error3'], 'd' => ['error4']]);
+		$author->errors('thing', ['this is a mistake']);
+		$user->errors(['a' => ['error1'], 'b' => ['error2']]);
+		$owner->errors(['c' => ['error3'], 'd' => ['error4']]);
 
 		$expected = ['a' => ['error1'], 'b' => ['error2']];
-		$this->assertEquals($expected, $entity->errors('user'));
+		$this->assertEquals($expected, $author->errors('user'));
 
 		$expected = ['c' => ['error3'], 'd' => ['error4']];
-		$this->assertEquals($expected, $entity->errors('owner'));
+		$this->assertEquals($expected, $author->errors('owner'));
 
-		$entity->set('multiple', [$entity2, $entity3]);
+		$author->set('multiple', [$user, $owner]);
 		$expected = [
 			['a' => ['error1'], 'b' => ['error2']],
 			['c' => ['error3'], 'd' => ['error4']]
 		];
-		$this->assertEquals($expected, $entity->errors('multiple'));
+		$this->assertEquals($expected, $author->errors('multiple'));
+
+		$user->set('author', $author);
+		$expected = ['thing' => ['this is a mistake']];
+		$this->assertEquals($expected, $author->errors('multiple.0.author'));
 	}
 
 /**

tests/test_app/TestApp/Model/Entity/Owner.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace TestApp\Model\Entity;
+
+use Cake\ORM\Entity;
+
+/**
+ * Tests entity class used for asserting correct loading
+ *
+ */
+class Owner extends Entity {
+
+}

tests/test_app/TestApp/Model/Entity/User.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace TestApp\Model\Entity;
+
+use Cake\ORM\Entity;
+
+/**
+ * Tests entity class used for asserting correct loading
+ *
+ */
+class User extends Entity {
+
+}