Eliminate unnecessary merge() if possible

Fix spring-projectsGH-3401

Author: quaff

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/JpaEntityInformation.java

@@ -30,6 +30,7 @@
  * @author Oliver Gierke
  * @author Thomas Darimont
  * @author Mark Paluch
+ * @author Yanming Zhou
  */
 public interface JpaEntityInformation<T, ID> extends EntityInformation<T, ID>, JpaEntityMetadata<T> {
 
@@ -39,6 +40,12 @@ public interface JpaEntityInformation<T, ID> extends EntityInformation<T, ID>, J
 	@Nullable
 	SingularAttribute<? super T, ?> getIdAttribute();
 
+	/**
+	 * Returns the version attribute of the entity.
+	 */
+	@Nullable
+	SingularAttribute<? super T, ?> getVersionAttribute();
+
 	/**
 	 * Returns the required identifier type.
 	 *

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/JpaMetamodelEntityInformation.java

@@ -47,14 +47,15 @@
 
 /**
  * Implementation of {@link org.springframework.data.repository.core.EntityInformation} that uses JPA {@link Metamodel}
- * to find the domain class' id field.
+ * to find the domain class' id and version field.
  *
  * @author Oliver Gierke
  * @author Thomas Darimont
  * @author Christoph Strobl
  * @author Mark Paluch
  * @author Jens Schauder
  * @author Greg Turnquist
+ * @author Yanming Zhou
  */
 public class JpaMetamodelEntityInformation<T, ID> extends JpaEntityInformationSupport<T, ID> {
 
@@ -191,6 +192,11 @@ public Class<ID> getIdType() {
 		return idMetadata.getSimpleIdAttribute();
 	}
 
+	@Override
+	public SingularAttribute<? super T, ?> getVersionAttribute() {
+		return versionAttribute.orElse(null);
+	}
+
 	@Override
 	public boolean hasCompositeId() {
 		return !idMetadata.hasSimpleId();

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java

@@ -195,7 +195,8 @@ public void delete(T entity) {
 			return;
 		}
 
-		entityManager.remove(entityManager.contains(entity) ? entity : entityManager.merge(entity));
+		boolean versioned = entityInformation.getVersionAttribute() != null; // GH-3401
+		entityManager.remove((entityManager.contains(entity) || !versioned) ? entity : entityManager.merge(entity));
 	}
 
 	@Override

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/support/JpaEntityInformationSupportUnitTests.java

@@ -42,6 +42,7 @@
  *
  * @author Oliver Gierke
  * @author Jens Schauder
+ * @author Yanming Zhou
  */
 @ExtendWith(MockitoExtension.class)
 @MockitoSettings(strictness = Strictness.LENIENT)
@@ -88,6 +89,11 @@ static class DummyJpaEntityInformation<T, ID> extends JpaEntityInformationSuppor
 			return null;
 		}
 
+		@Override
+		public SingularAttribute<? super T, ?> getVersionAttribute() {
+			return null;
+		}
+
 		@Override
 		public ID getId(T entity) {
 			return null;