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/main/java/org/springframework/data/mapping/IdentifierAccessor.java

@@ -0,0 +1,31 @@
+/*
+ * 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;
+
+/**
+ * Interface for a component allowing the access of identifier values.
+ * 
+ * @author Oliver Gierke
+ */
+public interface IdentifierAccessor {
+
+	/**
+	 * Returns the value of the identifier.
+	 * 
+	 * @return
+	 */
+	Object getIdentifier();
+}

src/main/java/org/springframework/data/mapping/PersistentEntity.java

@@ -179,4 +179,13 @@ public interface PersistentEntity<T, P extends PersistentProperty<P>> {
 	 * @since 1.10
 	 */
 	PersistentPropertyAccessor getPropertyAccessor(Object bean);
+
+	/**
+	 * Returns the {@link IdentifierAccessor} for the given bean.
+	 * 
+	 * @param bean must not be {@literal null}.
+	 * @return
+	 * @since 1.10
+	 */
+	IdentifierAccessor getIdentifierAccessor(Object bean);
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2013 by the original author(s).
+ * Copyright 2011-2014 by the original author(s).
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,7 @@ import org.springframework.core.annotation.AnnotationUtils;
 import org.springframework.data.annotation.TypeAlias;
 import org.springframework.data.mapping.Association;
 import org.springframework.data.mapping.AssociationHandler;
+import org.springframework.data.mapping.IdentifierAccessor;
 import org.springframework.data.mapping.PersistentEntity;
 import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.mapping.PersistentPropertyAccessor;
@@ -377,6 +378,39 @@ public class BasicPersistentEntity<T, P extends PersistentProperty<P>> implement
 		return new BeanWrapper<Object>(bean);
 	}
 
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mapping.PersistentEntity#getIdentifierAccessor(java.lang.Object)
+	 */
+	@Override
+	public IdentifierAccessor getIdentifierAccessor(Object bean) {
+
+		Assert.notNull(bean, "Targte bean must not be null!");
+		Assert.isTrue(getType().isInstance(bean), "Target bean is not of type of the persistent entity!");
+
+		return hasIdProperty() ? new IdPropertyIdentifierAccessor(this, bean) : NullReturningIdentifierAccessor.INSTANCE;
+	}
+
+	/**
+	 * A null-object implementation of {@link IdentifierAccessor} to be able to return an accessor for entities that do
+	 * not have an identifier property.
+	 *
+	 * @author Oliver Gierke
+	 */
+	private static enum NullReturningIdentifierAccessor implements IdentifierAccessor {
+
+		INSTANCE;
+
+		/* 
+		 * (non-Javadoc)
+		 * @see org.springframework.data.mapping.IdentifierAccessor#getIdentifier()
+		 */
+		@Override
+		public Object getIdentifier() {
+			return null;
+		}
+	}
+
 	/**
 	 * Simple {@link Comparator} adaptor to delegate ordering to the inverse properties of the association.
 	 * 

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

@@ -0,0 +1,60 @@
+/*
+ * 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 org.springframework.data.mapping.IdentifierAccessor;
+import org.springframework.data.mapping.PersistentEntity;
+import org.springframework.data.mapping.PersistentProperty;
+import org.springframework.data.mapping.PersistentPropertyAccessor;
+import org.springframework.util.Assert;
+
+/**
+ * Default implementation of {@link IdentifierAccessor}.
+ * 
+ * @author Christoph Strobl
+ * @author Oliver Gierke
+ * @since 1.10
+ */
+public class IdPropertyIdentifierAccessor implements IdentifierAccessor {
+
+	private final PersistentPropertyAccessor accessor;
+	private final PersistentProperty<?> idProperty;
+
+	/**
+	 * Creates a new {@link IdPropertyIdentifierAccessor} for the given {@link PersistentEntity} and
+	 * {@link ConvertingPropertyAccessor}.
+	 * 
+	 * @param entity must not be {@literal null}.
+	 * @param target must not be {@literal null}.
+	 */
+
+	public IdPropertyIdentifierAccessor(PersistentEntity<?, ?> entity, Object target) {
+
+		Assert.notNull(entity, "PersistentEntity must not be 'null'");
+		Assert.isTrue(entity.hasIdProperty(), "PersistentEntity does not have an identifier property!");
+
+		this.idProperty = entity.getIdProperty();
+		this.accessor = entity.getPropertyAccessor(target);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.keyvalue.core.IdentifierAccessor#getIdentifier()
+	 */
+	public Object getIdentifier() {
+		return accessor.getProperty(idProperty);
+	}
+}

src/main/java/org/springframework/data/repository/core/support/PersistentEntityInformation.java

@@ -18,7 +18,6 @@ package org.springframework.data.repository.core.support;
 import java.io.Serializable;
 
 import org.springframework.data.mapping.PersistentEntity;
-import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.mapping.model.BeanWrapper;
 import org.springframework.data.repository.core.EntityInformation;
 
@@ -50,14 +49,7 @@ public class PersistentEntityInformation<T, ID extends Serializable> extends Abs
 	 */
 	@Override
 	public ID getId(T entity) {
-
-		PersistentProperty<?> property = persistentEntity.getIdProperty();
-
-		if (property == null) {
-			return null;
-		}
-
-		return (ID) persistentEntity.getPropertyAccessor(entity).getProperty(property);
+		return (ID) persistentEntity.getIdentifierAccessor(entity).getIdentifier();
 	}
 
 	/*