From 3b0c73f109c1cc5ea16aa8cd32031d8d37a39265 Mon Sep 17 00:00:00 2001
From: Oliver Gierke <ogierke@pivotal.io>
Date: Thu, 4 May 2017 23:55:53 +0200
Subject: [PATCH] =?UTF-8?q?DATAREST-1067=20-=20EntityLookup.lookupEntity(?=
 =?UTF-8?q?=E2=80=A6)=20now=20returns=20Optional<T>.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../data/rest/core/config/EntityLookupConfiguration.java | 8 ++++++--
 .../data/rest/core/support/EntityLookup.java             | 2 +-
 .../core/support/UnwrappingRepositoryInvokerFactory.java | 9 ++++++---
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/config/EntityLookupConfiguration.java b/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/config/EntityLookupConfiguration.java
index 8ef8e06ee..7653530a2 100644
--- a/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/config/EntityLookupConfiguration.java
+++ b/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/config/EntityLookupConfiguration.java
@@ -208,8 +208,12 @@ class EntityLookupConfiguration implements EntityLookupRegistrar {
 		 * @see org.springframework.data.rest.core.support.EntityLookup#lookupEntity(java.io.Serializable)
 		 */
 		@Override
-		public Optional<Object> lookupEntity(Object id) {
-			return Optional.ofNullable(lookupInfo.getLookup().lookup(repository, id));
+		@SuppressWarnings("unchecked")
+		public Optional<T> lookupEntity(Object id) {
+
+			Object result = lookupInfo.getLookup().lookup(repository, id);
+
+			return Optional.class.isInstance(result) ? (Optional<T>) result : Optional.ofNullable((T) result);
 		}
 
 		/* 
diff --git a/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/EntityLookup.java b/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/EntityLookup.java
index 3a2b03282..4be1502d3 100644
--- a/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/EntityLookup.java
+++ b/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/EntityLookup.java
@@ -54,5 +54,5 @@ public interface EntityLookup<T> extends Plugin<Class<?>> {
 	 * @param id will never be {@literal null}.
 	 * @return can be {@literal null}.
 	 */
-	Optional<Object> lookupEntity(Object id);
+	Optional<T> lookupEntity(Object id);
 }
diff --git a/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/UnwrappingRepositoryInvokerFactory.java b/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/UnwrappingRepositoryInvokerFactory.java
index 26b691760..09e38d940 100644
--- a/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/UnwrappingRepositoryInvokerFactory.java
+++ b/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/UnwrappingRepositoryInvokerFactory.java
@@ -22,6 +22,7 @@ import java.io.Serializable;
 import java.lang.reflect.Method;
 import java.util.List;
 import java.util.Optional;
+import java.util.function.Supplier;
 
 import org.springframework.core.convert.converter.Converter;
 import org.springframework.data.domain.Pageable;
@@ -29,6 +30,7 @@ import org.springframework.data.domain.Sort;
 import org.springframework.data.repository.support.RepositoryInvoker;
 import org.springframework.data.repository.support.RepositoryInvokerFactory;
 import org.springframework.data.rest.core.util.Java8PluginRegistry;
+import org.springframework.data.util.Optionals;
 import org.springframework.util.Assert;
 import org.springframework.util.MultiValueMap;
 
@@ -89,9 +91,10 @@ public class UnwrappingRepositoryInvokerFactory implements RepositoryInvokerFact
 		@SuppressWarnings("unchecked")
 		public <T> Optional<T> invokeFindById(Object id) {
 
-			return (Optional<T>) lookup//
-					.map(it -> it.lookupEntity(id).orElse(Optional.empty()))//
-					.orElseGet(() -> delegate.invokeFindById(id));
+			Supplier<Optional<T>> viaLookup = () -> (Optional<T>) lookup.flatMap(it -> it.lookupEntity(id));
+			Supplier<Optional<T>> fallback = () -> delegate.invokeFindById(id);
+
+			return Optionals.firstNonEmpty(viaLookup, fallback);
 		}
 
 		/*