GH-2600 - Fix relproperties and simple relationship hydration.

Misses dynamic relationships right now.

Author: meistermeier

src/main/java/org/springframework/data/neo4j/core/mapping/DefaultNeo4jEntityConverter.java

@@ -32,6 +32,7 @@
 import java.util.function.Predicate;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
 import org.neo4j.driver.Value;
@@ -60,6 +61,7 @@
 import org.springframework.lang.NonNull;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
 
 /**
  * @author Michael J. Simons
@@ -538,6 +540,42 @@ private AssociationHandler<Neo4jPersistentProperty> populateFrom(MapAccessor que
 			boolean populatedScalarValue = !persistentProperty.isCollectionLike() && !persistentProperty.isMap()
 					&& propertyValueNotNull;
 
+			if (populatedCollection) {
+				createInstanceOfRelationships(persistentProperty, queryResult, (RelationshipDescription) association, baseDescription, relationshipsFromResult, nodesFromResult)
+						.ifPresent(value -> {
+							Collection<?> providedCollection = (Collection<?>) value;
+							Collection<?> existingValue = (Collection<?>) propertyValue;
+							Collection<Object> newValue = CollectionFactory.createCollection(existingValue.getClass(), providedCollection.size() + existingValue.size());
+
+							RelationshipDescription dings = (RelationshipDescription) association;
+							Map<Object, Object> mergedValues = new HashMap<>();
+							for (Object existingValueInCollection : existingValue) {
+								if (dings.hasRelationshipProperties()) {
+									Object existingIdPropertyValue = ((Neo4jPersistentEntity<?>) dings.getRelationshipPropertiesEntity()).getPropertyAccessor(existingValueInCollection).getProperty(((Neo4jPersistentEntity<?>) dings.getRelationshipPropertiesEntity()).getIdProperty());
+									mergedValues.put(existingIdPropertyValue, existingValueInCollection);
+								} else if (!dings.isDynamic()){ // should not happen because this is all inside populatedCollection (but better safe than sorry)
+									Object existingIdPropertyValue = ((Neo4jPersistentEntity<?>) dings.getTarget()).getPropertyAccessor(existingValueInCollection).getProperty(((Neo4jPersistentEntity<?>) dings.getTarget()).getIdProperty());
+									mergedValues.put(existingIdPropertyValue, existingValueInCollection);
+								}
+							}
+							for (Object providedValueInCollection : providedCollection) {
+								if (dings.hasRelationshipProperties()) {
+									Object existingIdPropertyValue = ((Neo4jPersistentEntity<?>) dings.getRelationshipPropertiesEntity()).getPropertyAccessor(providedValueInCollection).getProperty(((Neo4jPersistentEntity<?>) dings.getRelationshipPropertiesEntity()).getIdProperty());
+									mergedValues.put(existingIdPropertyValue, providedValueInCollection);
+								} else if (!dings.isDynamic()){ // should not happen because this is all inside populatedCollection (but better safe than sorry)
+									Object existingIdPropertyValue = ((Neo4jPersistentEntity<?>) dings.getTarget()).getPropertyAccessor(providedValueInCollection).getProperty(((Neo4jPersistentEntity<?>) dings.getTarget()).getIdProperty());
+									mergedValues.put(existingIdPropertyValue, providedValueInCollection);
+								}
+							}
+
+
+							newValue.addAll(mergedValues.values());
+							propertyAccessor.setProperty(persistentProperty, newValue);
+						});
+			}
+
+			// todo dynamic relationships with maps
+
 			boolean propertyAlreadyPopulated = populatedCollection || populatedMap || populatedScalarValue;
 
 			// avoid unnecessary re-assignment of values