DATACMNS-1015 - Introduced IdentifierAccessor.getRequiredIdentifier().

The new method allows to look up identifiers and immediately fail in the case of absence. Introduced the method as default method but also a new base type TargetAwareIdentifierAccessor to throw an exception with more context, i.e. the actual target bean we try to look up the identifier on.

Author: odrotbohm

Diff for: src/main/java/org/springframework/data/mapping/IdentifierAccessor.java

@@ -21,13 +21,27 @@
  * Interface for a component allowing the access of identifier values.
  * 
  * @author Oliver Gierke
+ * @see TargetAwareIdentifierAccessor
  */
 public interface IdentifierAccessor {
 
 	/**
 	 * Returns the value of the identifier.
 	 * 
-	 * @return
+	 * @return the identifier of the underlying instance.
 	 */
 	Optional<Object> getIdentifier();
+
+	/**
+	 * Returns the identifier of the underlying instance. Implementations are strongly recommended to extends either
+	 * {@link TargetAwareIdentifierAccessor} or override this method to add more context to the exception being thrown in
+	 * case of the absence of an identifier.
+	 * 
+	 * @return the identifier of the underlying instance
+	 * @throws IllegalStateException in case no identifier could be retrieved.
+	 * @since 2.0
+	 */
+	default Object getRequiredIdentifier() {
+		return getIdentifier().orElseThrow(() -> new IllegalStateException(String.format("Could not obtain identifier!")));
+	}
 }

Diff for: src/main/java/org/springframework/data/mapping/TargetAwareIdentifierAccessor.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2017 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;
+
+import lombok.RequiredArgsConstructor;
+
+import java.util.function.Supplier;
+
+/**
+ * {@link IdentifierAccessor} that is aware of the target bean to obtain the identifier from so that it can generate a
+ * more meaningful exception in case of an absent identifier and a call to {@link #getRequiredIdentifier()}.
+ * 
+ * @author Oliver Gierke
+ * @since 2.0
+ * @soundtrack Anika Nilles - Greenfield (Pikalar)
+ */
+@RequiredArgsConstructor
+public abstract class TargetAwareIdentifierAccessor implements IdentifierAccessor {
+
+	private final Supplier<Object> target;
+
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mapping.IdentifierAccessor#getRequiredIdentifier()
+	 */
+	@Override
+	public Object getRequiredIdentifier() {
+		return getIdentifier().orElseThrow(
+				() -> new IllegalStateException(String.format("Could not obtain identifier from %s!", target.get())));
+	}
+}

Diff for: src/main/java/org/springframework/data/mapping/model/BasicPersistentEntity.java

@@ -46,6 +46,7 @@
 import org.springframework.data.mapping.PropertyHandler;
 import org.springframework.data.mapping.SimpleAssociationHandler;
 import org.springframework.data.mapping.SimplePropertyHandler;
+import org.springframework.data.mapping.TargetAwareIdentifierAccessor;
 import org.springframework.data.util.Lazy;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.util.Assert;
@@ -438,7 +439,7 @@ public IdentifierAccessor getIdentifierAccessor(Object bean) {
 		Assert.isTrue(getType().isInstance(bean),
 				() -> String.format(TYPE_MISMATCH, bean.getClass().getName(), getType().getName()));
 
-		return hasIdProperty() ? new IdPropertyIdentifierAccessor(this, bean) : NullReturningIdentifierAccessor.INSTANCE;
+		return hasIdProperty() ? new IdPropertyIdentifierAccessor(this, bean) : new AbsentIdentifierAccessor(bean);
 	}
 
 	/**
@@ -447,9 +448,11 @@ public IdentifierAccessor getIdentifierAccessor(Object bean) {
 	 *
 	 * @author Oliver Gierke
 	 */
-	private static enum NullReturningIdentifierAccessor implements IdentifierAccessor {
+	private static class AbsentIdentifierAccessor extends TargetAwareIdentifierAccessor {
 
-		INSTANCE;
+		public AbsentIdentifierAccessor(Object target) {
+			super(() -> target);
+		}
 
 		/*
 		 * (non-Javadoc)

Diff for: src/main/java/org/springframework/data/mapping/model/IdPropertyIdentifierAccessor.java

@@ -21,6 +21,7 @@
 import org.springframework.data.mapping.PersistentEntity;
 import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.mapping.PersistentPropertyAccessor;
+import org.springframework.data.mapping.TargetAwareIdentifierAccessor;
 import org.springframework.util.Assert;
 
 /**
@@ -30,10 +31,10 @@
  * @author Oliver Gierke
  * @since 1.10
  */
-public class IdPropertyIdentifierAccessor implements IdentifierAccessor {
+public class IdPropertyIdentifierAccessor extends TargetAwareIdentifierAccessor {
 
 	private final PersistentPropertyAccessor accessor;
-	private final Optional<? extends PersistentProperty<?>> idProperty;
+	private final PersistentProperty<?> idProperty;
 
 	/**
 	 * Creates a new {@link IdPropertyIdentifierAccessor} for the given {@link PersistentEntity} and
@@ -42,13 +43,15 @@ public class IdPropertyIdentifierAccessor implements IdentifierAccessor {
 	 * @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!");
+		super(() -> target);
+
+		Assert.notNull(entity, "PersistentEntity must not be null!");
+		Assert.isTrue(entity.hasIdProperty(), "PersistentEntity must have an identifier property!");
+		Assert.notNull(target, "Target bean must not be null!");
 
-		this.idProperty = entity.getIdProperty();
+		this.idProperty = entity.getRequiredIdProperty();
 		this.accessor = entity.getPropertyAccessor(target);
 	}
 
@@ -57,6 +60,6 @@ public IdPropertyIdentifierAccessor(PersistentEntity<?, ?> entity, Object target
 	 * @see org.springframework.data.keyvalue.core.IdentifierAccessor#getIdentifier()
 	 */
 	public Optional<Object> getIdentifier() {
-		return idProperty.flatMap(accessor::getProperty);
+		return accessor.getProperty(idProperty);
 	}
 }

Diff for: src/test/java/org/springframework/data/mapping/TargetAwareIdentifierAccessorUnitTests.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2017 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;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.util.Optional;
+
+import org.junit.Test;
+
+/**
+ * Unit tests for {@link TargetAwareIdentifierAccessor}.
+ * 
+ * @author Oliver Gierke
+ * @soundtrack Anika Nilles - Greenfield (Pikalar)
+ */
+public class TargetAwareIdentifierAccessorUnitTests {
+
+	@Test // DATACMNS-1015
+	public void throwsExceptionContainingInformationAboutTargetIfIdentifierAbsent() {
+
+		Object sample = new Object();
+
+		IdentifierAccessor accessor = new TargetAwareIdentifierAccessor(() -> sample) {
+
+			@Override
+			public Optional<Object> getIdentifier() {
+				return Optional.empty();
+			}
+		};
+
+		assertThatExceptionOfType(IllegalStateException.class)//
+				.isThrownBy(() -> accessor.getRequiredIdentifier())//
+				.withMessageContaining(sample.toString());
+	}
+}