GH-2196 - Don't override relationships if they are different.

Relationship properties based relationships were overwritten due
to multiple `MERGE` statements if they had the same target node.

Author: meistermeier

src/main/java/org/springframework/data/neo4j/core/Neo4jTemplate.java

@@ -543,18 +543,27 @@ private <T> T processNestedRelations(Neo4jPersistentEntity<?> sourceEntity, Obje
 				}
 				stateMachine.markValueAsProcessed(relatedValueToStore);
 
+				Object idValue = idProperty != null
+						? relationshipContext
+							.getRelationshipPropertiesPropertyAccessor(relatedValueToStore).getProperty(idProperty)
+						: null;
+
+				boolean isNewRelationship = idValue == null;
+
 				CreateRelationshipStatementHolder statementHolder = neo4jMappingContext.createStatement(
-						sourceEntity, relationshipContext, relatedValueToStore);
+						sourceEntity, relationshipContext, relatedValueToStore, isNewRelationship);
 
 				Optional<Long> relationshipInternalId = neo4jClient.query(renderer.render(statementHolder.getStatement()))
 						.bind(convertIdValues(sourceEntity.getRequiredIdProperty(), fromId)) //
-							.to(Constants.FROM_ID_PARAMETER_NAME)
+							.to(Constants.FROM_ID_PARAMETER_NAME) //
 						.bind(relatedInternalId) //
 							.to(Constants.TO_ID_PARAMETER_NAME) //
+						.bind(idValue) //
+							.to(Constants.NAME_OF_KNOWN_RELATIONSHIP_PARAM) //
 						.bindAll(statementHolder.getProperties())
 						.fetchAs(Long.class).one();
 
-				if (idProperty != null) {
+				if (idProperty != null && isNewRelationship) {
 					relationshipContext
 							.getRelationshipPropertiesPropertyAccessor(relatedValueToStore)
 							.setProperty(idProperty, relationshipInternalId.get());

src/main/java/org/springframework/data/neo4j/core/ReactiveNeo4jTemplate.java

@@ -674,8 +674,14 @@ private Mono<Void> processNestedRelations(Neo4jPersistentEntity<?> sourceEntity,
 														relatedInternalId);
 											}
 
+											Object idValue = idProperty != null
+													? relationshipContext
+													.getRelationshipPropertiesPropertyAccessor(relatedValueToStore).getProperty(idProperty)
+													: null;
+
+											boolean isNewRelationship = idValue == null;
 											CreateRelationshipStatementHolder statementHolder = neo4jMappingContext.createStatement(
-													sourceEntity, relationshipContext, relatedValueToStore);
+													sourceEntity, relationshipContext, relatedValueToStore, isNewRelationship);
 
 											// in case of no properties the bind will just return an empty map
 											Mono<Long> relationshipCreationMonoNested = neo4jClient
@@ -684,10 +690,12 @@ private Mono<Void> processNestedRelations(Neo4jPersistentEntity<?> sourceEntity,
 														.to(Constants.FROM_ID_PARAMETER_NAME) //
 													.bind(relatedInternalId) //
 														.to(Constants.TO_ID_PARAMETER_NAME) //
+													.bind(idValue) //
+														.to(Constants.NAME_OF_KNOWN_RELATIONSHIP_PARAM) //
 													.bindAll(statementHolder.getProperties())
 													.fetchAs(Long.class).one()
 													.doOnNext(relationshipInternalId -> {
-														if (idProperty != null) {
+														if (idProperty != null && isNewRelationship) {
 															relationshipContext
 																	.getRelationshipPropertiesPropertyAccessor(relatedValueToStore)
 																	.setProperty(idProperty, relationshipInternalId);

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

@@ -52,6 +52,7 @@ public final class Constants {
 	 */
 	public static final String NAME_OF_STATIC_LABELS_PARAM = "__staticLabels__";
 	public static final String NAME_OF_ENTITY_LIST_PARAM = "__entities__";
+	public static final String NAME_OF_KNOWN_RELATIONSHIP_PARAM = "__knownRelationShipId__";
 	public static final String NAME_OF_KNOWN_RELATIONSHIPS_PARAM = "__knownRelationShipIds__";
 	public static final String NAME_OF_PATHS = "__paths__";
 	public static final String NAME_OF_ALL_PROPERTIES = "__allProperties__";

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

@@ -364,7 +364,9 @@ public Statement prepareSaveOfRelationship(Neo4jPersistentEntity<?> neo4jPersist
 
 	@NonNull
 	public Statement prepareSaveOfRelationshipWithProperties(Neo4jPersistentEntity<?> neo4jPersistentEntity,
-			RelationshipDescription relationship, @Nullable String dynamicRelationshipType) {
+				 RelationshipDescription relationship,
+				 boolean isNew,
+				 @Nullable String dynamicRelationshipType) {
 
 		Assert.isTrue(relationship.hasRelationshipProperties(),
 				"Properties required to create a relationship with properties");
@@ -383,11 +385,16 @@ public Statement prepareSaveOfRelationshipWithProperties(Neo4jPersistentEntity<?
 						startNode.relationshipFrom(endNode, type))
 				.named(RELATIONSHIP_NAME);
 
-		return match(startNode)
+		StatementBuilder.OngoingReadingWithWhere startAndEndNodeMatch = match(startNode)
 				.where(neo4jPersistentEntity.isUsingInternalIds() ? startNode.internalId().isEqualTo(idParameter)
 						: startNode.property(idPropertyName).isEqualTo(idParameter))
-				.match(endNode).where(endNode.internalId().isEqualTo(parameter(Constants.TO_ID_PARAMETER_NAME)))
-				.merge(relationshipFragment)
+				.match(endNode).where(endNode.internalId().isEqualTo(parameter(Constants.TO_ID_PARAMETER_NAME)));
+
+		StatementBuilder.ExposesSet createOrMatch = isNew
+				? startAndEndNodeMatch.create(relationshipFragment)
+				: startAndEndNodeMatch.match(relationshipFragment)
+					.where(Functions.id(relationshipFragment).isEqualTo(Cypher.parameter(Constants.NAME_OF_KNOWN_RELATIONSHIP_PARAM)));
+		return createOrMatch
 				.mutate(RELATIONSHIP_NAME, relationshipProperties)
 				.returning(Functions.id(relationshipFragment))
 				.build();

src/main/java/org/springframework/data/neo4j/core/mapping/Neo4jMappingContext.java

@@ -319,7 +319,10 @@ public void setApplicationContext(ApplicationContext applicationContext) throws
 		this.beanFactory = applicationContext.getAutowireCapableBeanFactory();
 	}
 
-	public CreateRelationshipStatementHolder createStatement(Neo4jPersistentEntity<?> neo4jPersistentEntity, NestedRelationshipContext relationshipContext, Object relatedValue) {
+	public CreateRelationshipStatementHolder createStatement(Neo4jPersistentEntity<?> neo4jPersistentEntity,
+															 NestedRelationshipContext relationshipContext,
+															 Object relatedValue,
+															 boolean isNewRelationship) {
 
 		if (relationshipContext.hasRelationshipWithProperties()) {
 			MappingSupport.RelationshipPropertiesWithEntityHolder relatedValueEntityHolder =
@@ -342,18 +345,20 @@ public CreateRelationshipStatementHolder createStatement(Neo4jPersistentEntity<?
 			}
 			return createStatementForRelationShipWithProperties(
 					neo4jPersistentEntity, relationshipContext,
-					dynamicRelationshipType, relatedValueEntityHolder
+					dynamicRelationshipType, relatedValueEntityHolder, isNewRelationship
 			);
 		} else {
 			return createStatementForRelationshipWithoutProperties(neo4jPersistentEntity, relationshipContext, relatedValue);
 		}
 	}
 
 	private CreateRelationshipStatementHolder createStatementForRelationShipWithProperties(Neo4jPersistentEntity<?> neo4jPersistentEntity,
-			NestedRelationshipContext relationshipContext, @Nullable  String dynamicRelationshipType, MappingSupport.RelationshipPropertiesWithEntityHolder relatedValue) {
+			NestedRelationshipContext relationshipContext, @Nullable String dynamicRelationshipType,
+		    MappingSupport.RelationshipPropertiesWithEntityHolder relatedValue, boolean isNewRelationship) {
 
 		Statement relationshipCreationQuery = CypherGenerator.INSTANCE.prepareSaveOfRelationshipWithProperties(
-						neo4jPersistentEntity, relationshipContext.getRelationship(), dynamicRelationshipType);
+						neo4jPersistentEntity, relationshipContext.getRelationship(), isNewRelationship, dynamicRelationshipType);
+
 		Map<String, Object> propMap = new HashMap<>();
 		// write relationship properties
 		getEntityConverter().write(relatedValue.getRelationshipProperties(), propMap);

src/test/java/org/springframework/data/neo4j/integration/imperative/RepositoryIT.java

@@ -2367,6 +2367,33 @@ void saveRelatedEntitesWithSameCustomIdsAndPlainRelationships(
 				assertThat(list).hasSize(0);
 			}
 		}
+
+		@Test // GH-2196
+		void saveSameNodeWithDoubleRelationship(@Autowired HobbyWithRelationshipWithPropertiesRepository repository) {
+			AltHobby hobby = new AltHobby();
+			hobby.setName("Music");
+
+			AltPerson altPerson = new AltPerson("Freddie");
+
+			AltLikedByPersonRelationship rel1 = new AltLikedByPersonRelationship();
+			rel1.setRating(5);
+			rel1.setAltPerson(altPerson);
+
+			AltLikedByPersonRelationship rel2 = new AltLikedByPersonRelationship();
+			rel2.setRating(1);
+			rel2.setAltPerson(altPerson);
+
+			hobby.getLikedBy().add(rel1);
+			hobby.getLikedBy().add(rel2);
+			repository.save(hobby);
+
+			hobby = repository.loadFromCustomQuery(altPerson.getId());
+			assertThat(hobby.getName()).isEqualTo("Music");
+			List<AltLikedByPersonRelationship> likedBy = hobby.getLikedBy();
+			assertThat(likedBy).hasSize(2);
+
+			assertThat(likedBy).containsExactlyInAnyOrder(rel1, rel2);
+		}
 	}
 
 	@Nested

src/test/java/org/springframework/data/neo4j/integration/reactive/ReactiveRepositoryIT.java

@@ -2085,6 +2085,37 @@ void saveBidirectionalRelationship(@Autowired BidirectionalStartRepository repos
 				assertThat(records).hasSize(1);
 			}
 		}
+
+		@Test // GH-2196
+		void saveSameNodeWithDoubleRelationship(@Autowired ReactiveHobbyWithRelationshipWithPropertiesRepository repository) {
+			AltHobby hobby = new AltHobby();
+			hobby.setName("Music");
+
+			AltPerson altPerson = new AltPerson("Freddie");
+
+			AltLikedByPersonRelationship rel1 = new AltLikedByPersonRelationship();
+			rel1.setRating(5);
+			rel1.setAltPerson(altPerson);
+
+			AltLikedByPersonRelationship rel2 = new AltLikedByPersonRelationship();
+			rel2.setRating(1);
+			rel2.setAltPerson(altPerson);
+
+			hobby.getLikedBy().add(rel1);
+			hobby.getLikedBy().add(rel2);
+			StepVerifier.create(repository.save(hobby))
+					.expectNextCount(1)
+					.verifyComplete();
+
+			StepVerifier.create(repository.loadFromCustomQuery(altPerson.getId()))
+					.assertNext(loadedHobby -> {
+						assertThat(loadedHobby.getName()).isEqualTo("Music");
+						List<AltLikedByPersonRelationship> likedBy = loadedHobby.getLikedBy();
+						assertThat(likedBy).hasSize(2);
+						assertThat(likedBy).containsExactlyInAnyOrder(rel1, rel2);
+					})
+					.verifyComplete();
+		}
 	}
 
 	@Nested