DATACMNS-1162 - Improved support for immutable aggregates.

AbstractAggregateRoot is now generified to be able to use its concrete type on methods returning an instance of itself. Added new methods andEvent(…) and andEventsFrom(…) to easily transfer events from another aggregate instance. Added unit tests for fundamental functionality of the base class.

src/main/java/org/springframework/data/domain/AbstractAggregateRoot.java

@@ -33,7 +33,7 @@ import org.springframework.util.Assert;
  * @author Christoph Strobl
  * @since 1.13
  */
-public class AbstractAggregateRoot {
+public class AbstractAggregateRoot<A extends AbstractAggregateRoot<A>> {
 
 	private transient final @Transient List<Object> domainEvents = new ArrayList<>();
 
@@ -41,7 +41,8 @@ public class AbstractAggregateRoot {
 	 * Registers the given event object for publication on a call to a Spring Data repository's save methods.
 	 * 
 	 * @param event must not be {@literal null}.
-	 * @return
+	 * @return the event that has been added.
+	 * @see #andEvent(Object)
 	 */
 	protected <T> T registerEvent(T event) {
 
@@ -67,4 +68,34 @@ public class AbstractAggregateRoot {
 	protected Collection<Object> domainEvents() {
 		return Collections.unmodifiableList(domainEvents);
 	}
+
+	/**
+	 * Adds all events contained in the given aggregate to the current one.
+	 * 
+	 * @param aggregate must not be {@literal null}.
+	 * @return the aggregate
+	 */
+	protected final A andEventsFrom(A aggregate) {
+
+		Assert.notNull(aggregate, "Aggregate must not be null!");
+
+		this.domainEvents.addAll(aggregate.domainEvents());
+
+		return (A) this;
+	}
+
+	/**
+	 * Adds the given event to the aggregate for later publication when calling a Spring Data repository's save-method.
+	 * Does the same as {@link #registerEvent(Object)} but returns the aggregate instead of the event.
+	 * 
+	 * @param event must not be {@literal null}.
+	 * @return the aggregate
+	 * @see #registerEvent(Object)
+	 */
+	protected final A andEvent(Object event) {
+
+		registerEvent(event);
+
+		return (A) this;
+	}
 }