diff --git a/core/bootstrap.md b/core/bootstrap.md
index d3c87c7441d..640a976f33c 100644
--- a/core/bootstrap.md
+++ b/core/bootstrap.md
@@ -139,6 +139,7 @@ use Symfony\Component\Serializer\Normalizer\ProblemNormalizer;
 use Symfony\Component\Serializer\Normalizer\UnwrappingDenormalizer;
 use Symfony\Component\Serializer\Serializer;
 
+/** @deprecated since API Platform 2.7, will be removed in API Platform 3.0 */
 $allowPlainIdentifiers = false;
 $debug = true;
 $defaultContext = [];
diff --git a/core/configuration.md b/core/configuration.md
index a8e1fa45989..2de67004b3b 100644
--- a/core/configuration.md
+++ b/core/configuration.md
@@ -32,6 +32,7 @@ api_platform:
     path_segment_name_generator: 'api_platform.path_segment_name_generator.underscore'
 
     # Allow using plain IDs for JSON format.
+    # Deprecated since API Platform 2.7, will be removed in API Platform 3.0
     allow_plain_identifiers: false
 
     validator:
diff --git a/core/serialization.md b/core/serialization.md
index 426c4b9d6c2..9d5f3b286a8 100644
--- a/core/serialization.md
+++ b/core/serialization.md
@@ -408,6 +408,54 @@ class Person
 
 ```
 
+### Plain Identifiers
+
+Instead of sending an IRI to set a relation, you may want to send a plain identifier. To do so, you must create your own denormalizer:
+
+```php
+<?php
+// api/src/Serializer/PlainIdentifierDenormalizer
+
+namespace App\Serializer;
+
+use ApiPlatform\Core\Api\IriConverterInterface;
+use App\Entity\Dummy;
+use App\Entity\RelatedDummy;
+use Symfony\Component\Serializer\Normalizer\ContextAwareDenormalizerInterface;
+use Symfony\Component\Serializer\Normalizer\DenormalizerAwareInterface;
+use Symfony\Component\Serializer\Normalizer\DenormalizerAwareTrait;
+
+class PlainIdentifierDenormalizer implements ContextAwareDenormalizerInterface, DenormalizerAwareInterface
+{
+    use DenormalizerAwareTrait;
+
+    private $iriConverter;
+
+    public function __construct(IriConverterInterface $iriConverter)
+    {
+        $this->iriConverter = $iriConverter;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function denormalize($data, $class, $format = null, array $context = [])
+    {
+        $data['relatedDummy'] = $this->iriConverter->getItemIriFromResourceClass(RelatedDummy::class, ['id' => $data['relatedDummy']]);
+
+        return $this->denormalizer->denormalize($data, $class, $format, $context + [__CLASS__ => true]);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function supportsDenormalization($data, $type, $format = null, array $context = []): bool
+    {
+        return \in_array($format, ['json', 'jsonld'], true) && is_a($type, Dummy::class, true) && !empty($data['relatedDummy']) && !isset($context[__CLASS__]);
+    }
+}
+```
+
 ## Calculated Field
 
 Sometimes you need to expose calculated fields. This can be done by leveraging the groups. This time not on a property, but on a method.