Fixed issue with a wrong cast to Collection

Resolves issue #461

core/src/main/java/org/axonframework/commandhandling/model/inspection/AggregateMemberAnnotatedChildEntityCollectionDefinition.java

@@ -25,7 +25,6 @@
 import org.axonframework.eventhandling.EventMessage;
 
 import java.lang.reflect.Field;
-import java.util.Collection;
 import java.util.Map;
 import java.util.Objects;
 import java.util.stream.Stream;
@@ -86,7 +85,9 @@ protected <T> Stream<Object> resolveEventTargets(EventMessage message,
                                                      T parentEntity,
                                                      Field field,
                                                      ForwardingMode eventForwardingMode) {
-        Collection<Object> fieldValue = ReflectionUtils.getFieldValue(field, parentEntity);
-        return fieldValue == null ? Stream.empty() : eventForwardingMode.filterCandidates(message, fieldValue.stream());
+        Iterable<Object> fieldValue = ReflectionUtils.getFieldValue(field, parentEntity);
+        return fieldValue == null
+                ? Stream.empty()
+                : eventForwardingMode.filterCandidates(message, StreamSupport.stream(fieldValue.spliterator(), false));
     }
 }

core/src/test/java/org/axonframework/commandhandling/model/inspection/AnnotatedAggregateMetaModelFactoryTest.java

@@ -35,6 +35,7 @@
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.Consumer;
 import java.util.function.Supplier;
 
 import static org.axonframework.commandhandling.GenericCommandMessage.asCommandMessage;
@@ -330,13 +331,13 @@ private static class SomeRecursiveEntity {
         private final String entityId;
 
         @AggregateMember
-        private final Collection<SomeRecursiveEntity> children;
+        private final SomeIterable<SomeRecursiveEntity> children;
 
         public SomeRecursiveEntity(Supplier<Collection<SomeRecursiveEntity>> supplier, SomeRecursiveEntity parent, String entityId) {
             this.supplier = supplier;
             this.parent = parent;
             this.entityId = entityId;
-            this.children = supplier.get();
+            this.children = new SomeIterable<>(supplier.get());
         }
 
         public SomeRecursiveEntity getChild(String childId) {
@@ -419,4 +420,46 @@ public String getId() {
             return id;
         }
     }
+
+    /**
+     * Wrapper implementation to ensure that the @AggregateMember field is solely triggered by the fact it implements
+     * Iterable, and doesn't depend on any other interface being declared. See issue #461.
+     *
+     * @param <T> The type contained in this iterable
+     */
+    private static class SomeIterable<T> implements Iterable<T> {
+
+        private final Collection<T> contents;
+
+        public SomeIterable(Collection<T> contents) {
+            this.contents = contents;
+        }
+
+        @Override
+        public Iterator<T> iterator() {
+            return contents.iterator();
+        }
+
+        @Override
+        public void forEach(Consumer<? super T> action) {
+            contents.forEach(action);
+        }
+
+        @Override
+        public Spliterator<T> spliterator() {
+            return contents.spliterator();
+        }
+
+        public boolean add(T item) {
+            return contents.add(item);
+        }
+
+        public boolean remove(T item) {
+            return contents.remove(item);
+        }
+
+        public int size() {
+            return contents.size();
+        }
+    }
 }