DATACMNS-1325 - Added dedicated identifier accessor for Persistable entities.

BasicPersistentEntity now returns a dedicated IdentifierAccessor that uses Persistable.getId() in case the entity implements Persistable.

src/main/java/org/springframework/data/mapping/model/BasicPersistentEntity.java

@@ -34,6 +34,7 @@ import java.util.stream.Collectors;
 
 import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.data.annotation.TypeAlias;
+import org.springframework.data.domain.Persistable;
 import org.springframework.data.mapping.Alias;
 import org.springframework.data.mapping.Association;
 import org.springframework.data.mapping.AssociationHandler;
@@ -473,6 +474,10 @@ public class BasicPersistentEntity<T, P extends PersistentProperty<P>> implement
 		Assert.isTrue(getType().isInstance(bean),
 				() -> String.format(TYPE_MISMATCH, bean.getClass().getName(), getType().getName()));
 
+		if (Persistable.class.isAssignableFrom(getType())) {
+			return new PersistableIdentifierAccessor((Persistable<?>) bean);
+		}
+
 		return hasIdProperty() ? new IdPropertyIdentifierAccessor(this, bean) : new AbsentIdentifierAccessor(bean);
 	}
 

src/main/java/org/springframework/data/mapping/model/PersistableIdentifierAccessor.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mapping.model;
+
+import org.springframework.data.domain.Persistable;
+import org.springframework.data.mapping.IdentifierAccessor;
+import org.springframework.data.mapping.TargetAwareIdentifierAccessor;
+import org.springframework.lang.Nullable;
+
+/**
+ * {@link IdentifierAccessor} that invokes {@link Persistable#getId()}.
+ * 
+ * @author Oliver Gierke
+ */
+class PersistableIdentifierAccessor extends TargetAwareIdentifierAccessor {
+
+	private final Persistable<?> target;
+
+	/**
+	 * Creates a new {@link PersistableIdentifierAccessor} for the given target.
+	 * 
+	 * @param target must not be {@literal null}.
+	 */
+	public PersistableIdentifierAccessor(Persistable<?> target) {
+
+		super(target);
+
+		this.target = target;
+	}
+
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mapping.IdentifierAccessor#getIdentifier()
+	 */
+	@Override
+	@Nullable
+	public Object getIdentifier() {
+		return target.getId();
+	}
+}