Allow updating nested resource on POST

Fixes api-platform#1624, api-platform#1363, api-platform#427

Author: jdeniau

features/hydra/error.feature

@@ -85,6 +85,7 @@ Feature: Error handling
     And the JSON node "hydra:description" should exist
     And the JSON node "trace" should exist
 
+    @dropSchema
     Scenario: Get an error during update of an existing resource with a non-allowed update operation
       When I add "Content-Type" header equal to "application/ld+json"
       And I send a "POST" request to "/dummies" with body:
@@ -103,23 +104,39 @@ Feature: Error handling
       And the JSON node "hydra:description" should be equal to "Update is not allowed for this operation."
       And the JSON node "trace" should exist
 
-    Scenario: Get an error during update of an existing relation with a non-allowed update operation
+    @createSchema
+    Scenario: Populate database with related dummies. Check that id will be "/related_dummies/1"
+      Given I add "Content-Type" header equal to "application/ld+json"
+      And I send a "POST" request to "/related_dummies" with body:
+      """
+      {
+          "@type": "https://schema.org/Product",
+          "symfony": "laravel"
+      }
+      """
+      Then the response status code should be 201
+      And the response should be in JSON
+      And the JSON node "@id" should be equal to "/related_dummies/1"
+      And the JSON node "symfony" should be equal to "laravel"
+
+    @dropSchema
+    Scenario: Do not get an error during update of an existing relation with a non-allowed update operation
       When I add "Content-Type" header equal to "application/ld+json"
       And I send a "POST" request to "/relation_embedders" with body:
       """
       {
         "anotherRelated": {
-          "@id": "/related_dummies/2",
+          "@id": "/related_dummies/1",
           "@type": "https://schema.org/Product",
           "symfony": "phalcon"
         }
       }
       """
-      Then the response status code should be 400
+      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 node "@context" should be equal to "/contexts/Error"
-      And the JSON node "@type" should be equal to "hydra:Error"
-      And the JSON node "hydra:title" should be equal to "An error occurred"
-      And the JSON node "hydra:description" should be equal to "Update is not allowed for this operation."
-      And the JSON node "trace" should exist
+      And the JSON node "@context" should be equal to "/contexts/RelationEmbedder"
+      And the JSON node "@type" should be equal to "RelationEmbedder"
+      And the JSON node "@id" should be equal to "/relation_embedders/1"
+      And the JSON node "anotherRelated.@id" should be equal to "/related_dummies/1"
+      And the JSON node "anotherRelated.symfony" should be equal to "phalcon"

src/Serializer/AbstractItemNormalizer.php

@@ -297,6 +297,7 @@ private function denormalizeRelation(string $attributeName, PropertyMetadata $pr
             ($propertyMetadata->isWritableLink() && \is_array($value))
         ) {
             $context['resource_class'] = $className;
+            $context['api_allow_update'] = true;
 
             return $this->serializer->denormalize($value, $className, $format, $context);
         }