Fix relations denormalization with plain ids (#1855)

* On invalid iri error with plain identifiers, use the data provider

If a resource property is writable, we can't use plain identifiers, and
end up with a iri error, while we explicit allowed plain identifiers.

* Make an appropriare exception for invalid value on item normalizer

* Add a behat test for plain id relations

Author: Taluu

features/main/relation.feature

@@ -512,13 +512,50 @@ Feature: Relations support
     }
     """
 
+  Scenario: Passing a (valid) plain identifier on a relation
+    When I add "Content-Type" header equal to "application/json"
+    And I send a "POST" request to "/dummies" with body:
+    """
+    {
+      "relatedDummy": "1",
+      "relatedDummies": ["1"],
+      "name": "Dummy with plain relations"
+    }
+    """
+    Then the response status code should be 201
+    And the response should be in JSON
+    And the header "Content-Type" should be equal to "application/ld+json; charset=utf-8"
+    And the JSON should be equal to:
+    """
+    {
+      "@context":"/contexts/Dummy",
+      "@id":"/dummies/2",
+      "@type":"Dummy",
+      "description":null,
+      "dummy":null,
+      "dummyBoolean":null,
+      "dummyDate":null,
+      "dummyFloat":null,
+      "dummyPrice":null,
+      "relatedDummy":"/related_dummies/1",
+      "relatedDummies":["/related_dummies/1"],
+      "jsonData":[],
+      "arrayData":[],
+      "name_converted":null,
+      "id":2,
+      "name":"Dummy with plain relations",
+      "alias":null,
+      "foo":null
+    }
+    """
+
   @dropSchema
   Scenario: Passing an invalid IRI to a relation
     When I add "Content-Type" header equal to "application/ld+json"
     And I send a "POST" request to "/relation_embedders" with body:
     """
     {
-      "related": "certainly not an iri"
+      "related": "certainly not an iri and not a plain identifier"
     }
     """
     Then the response status code should be 400

src/Exception/InvalidValueException.php

@@ -0,0 +1,18 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace ApiPlatform\Core\Exception;
+
+class InvalidValueException extends InvalidArgumentException
+{
+}

src/Serializer/AbstractItemNormalizer.php

@@ -18,6 +18,7 @@
 use ApiPlatform\Core\Api\ResourceClassResolverInterface;
 use ApiPlatform\Core\DataProvider\ItemDataProviderInterface;
 use ApiPlatform\Core\Exception\InvalidArgumentException;
+use ApiPlatform\Core\Exception\InvalidValueException;
 use ApiPlatform\Core\Exception\ItemNotFoundException;
 use ApiPlatform\Core\Metadata\Property\Factory\PropertyMetadataFactoryInterface;
 use ApiPlatform\Core\Metadata\Property\Factory\PropertyNameCollectionFactoryInterface;
@@ -157,7 +158,7 @@ protected function getAllowedAttributes($classOrObject, array $context, $attribu
     protected function setAttributeValue($object, $attribute, $value, $format = null, array $context = [])
     {
         if (!\is_string($attribute)) {
-            throw new InvalidArgumentException('Invalid value provided (invalid IRI?).');
+            throw new InvalidValueException('Invalid value provided (invalid IRI?).');
         }
 
         $propertyMetadata = $this->propertyMetadataFactory->create($context['resource_class'], $attribute, $this->getFactoryOptions($context));
@@ -304,7 +305,13 @@ protected function denormalizeRelation(string $attributeName, PropertyMetadata $
             $context['resource_class'] = $className;
             $context['api_allow_update'] = true;
 
-            return $this->serializer->denormalize($value, $className, $format, $context);
+            try {
+                return $this->serializer->denormalize($value, $className, $format, $context);
+            } catch (InvalidValueException $e) {
+                if (!$this->allowPlainIdentifiers || null === $this->itemDataProvider) {
+                    throw $e;
+                }
+            }
         }
 
         if (!\is_array($value)) {