DATACMNS-599 - Introduced IdentifierAccessor API.

PersistentEntity now exposes an getIdentifierAccessor(…)-method that allows obtaining the identifier of an entity without using a PersistentProperty instance. This allows advanced scenarios (like multi-property identifiers). Also we can use store specific means to optimize id lookups to e.g. avoid proxy initialization for lazy loading proxies.

src/test/java/org/springframework/data/mapping/model/IdPropertyIdentifierAccessorUnitTests.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2014 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 static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.mapping.IdentifierAccessor;
+import org.springframework.data.mapping.context.SampleMappingContext;
+
+/**
+ * @author Oliver Gierke
+ */
+public class IdPropertyIdentifierAccessorUnitTests {
+
+	SampleMappingContext mappingContext = new SampleMappingContext();
+
+	/**
+	 * @see DATACMNS-599
+	 */
+	@Test(expected = IllegalArgumentException.class)
+	public void rejectsEntityWithoutIdentifierProperty() {
+
+		new IdPropertyIdentifierAccessor(mappingContext.getPersistentEntity(Sample.class), new Sample());
+	}
+
+	/**
+	 * @see DATACMNS-599
+	 */
+	@Test(expected = IllegalArgumentException.class)
+	public void rejectsNullBean() {
+
+		new IdPropertyIdentifierAccessor(mappingContext.getPersistentEntity(SampleWithId.class), null);
+	}
+
+	/**
+	 * @see DATACMNS-599
+	 */
+	@Test
+	public void returnsIdentifierValue() {
+
+		SampleWithId sample = new SampleWithId();
+		sample.id = 1L;
+
+		IdentifierAccessor accessor = new IdPropertyIdentifierAccessor(
+				mappingContext.getPersistentEntity(SampleWithId.class), sample);
+
+		assertThat(accessor.getIdentifier(), is((Object) sample.id));
+	}
+
+	static class Sample {}
+
+	static class SampleWithId {
+		@Id Long id;
+	}
+}