GH-2583 - Improve relationship mapping.

Accept maximum of two iterations for a relationship before it gets removed from the candidate list.

Closes #2583

Author: meistermeier

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

@@ -615,6 +615,13 @@ private Optional<Object> createInstanceOfRelationships(Neo4jPersistentProperty p
 				for (Relationship possibleRelationship : allMatchingTypeRelationshipsInResult) {
 					if (targetIdSelector.apply(possibleRelationship) == targetNodeId) {
 
+						// Reduce the amount of relationships in the candidate list.
+						// If this relationship got processed twice (OUTGOING, INCOMING), it is never needed again
+						// and therefor should not be in the list.
+						// Otherwise, for highly linked data it could potentially cause a StackOverflowError.
+						if (knownObjects.hasProcessedRelationshipCompletely(possibleRelationship.id())) {
+							relationshipsFromResult.remove(possibleRelationship);
+						}
 						// If the target is the same(equal) node, get the related object from the cache.
 						// Avoiding the call to the map method also breaks an endless cycle of trying to finish
 						// the property population of _this_ object.
@@ -777,6 +784,8 @@ static class KnownObjects {
 		private final Set<Long> previousRecords = new HashSet<>();
 		private final Set<Long> idsInCreation = new HashSet<>();
 
+		private final Map<Long, Integer> processedRelationships = new HashMap<>();
+
 		private void storeObject(@Nullable Long internalId, Object object) {
 			if (internalId == null) {
 				return;
@@ -863,6 +872,25 @@ private boolean alreadyMappedInPreviousRecord(@Nullable Long internalId) {
 			}
 		}
 
+		private boolean hasProcessedRelationshipCompletely(Long relationshipId) {
+			try {
+				write.lock();
+				read.lock();
+
+				int amount = processedRelationships.computeIfAbsent(relationshipId, s -> 0);
+				if (amount == 2) {
+					return true;
+				}
+
+				processedRelationships.put(relationshipId, amount + 1);
+				return false;
+
+			} finally {
+				write.unlock();
+				read.unlock();
+			}
+		}
+
 		/**
 		 * Mark all currently existing objects as mapped.
 		 */

src/test/java/org/springframework/data/neo4j/integration/issues/IssuesIT.java

@@ -53,6 +53,8 @@
 import org.springframework.context.annotation.ComponentScan;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.dao.DataIntegrityViolationException;
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Sort;
 import org.springframework.data.mapping.PersistentPropertyAccessor;
 import org.springframework.data.neo4j.core.DatabaseSelectionProvider;
@@ -123,6 +125,8 @@
 import org.springframework.data.neo4j.integration.issues.gh2579.TableAndColumnRelation;
 import org.springframework.data.neo4j.integration.issues.gh2579.TableNode;
 import org.springframework.data.neo4j.integration.issues.gh2579.TableRepository;
+import org.springframework.data.neo4j.integration.issues.gh2583.GH2583Node;
+import org.springframework.data.neo4j.integration.issues.gh2583.GH2583Repository;
 import org.springframework.data.neo4j.integration.misc.ConcreteImplementationTwo;
 import org.springframework.data.neo4j.repository.config.EnableNeo4jRepositories;
 import org.springframework.data.neo4j.repository.query.QueryFragmentsAndParameters;
@@ -169,6 +173,7 @@ protected static void setupData(@Autowired BookmarkCapture bookmarkCapture) {
 				setupGH2328(transaction);
 				setupGH2459(transaction);
 				setupGH2572(transaction);
+				setupGH2583(transaction);
 
 				transaction.commit();
 			}
@@ -217,6 +222,21 @@ private static void setupGH2459(QueryRunner queryRunner) {
 				CREATE (po1)-[:hasPet]->(a3)""").consume();
 	}
 
+	private static void setupGH2583(QueryRunner queryRunner) {
+		queryRunner.run("""
+				CREATE (n:GH2583Node)-[:LINKED]->(m:GH2583Node)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)
+				-[:LINKED]->(n)-[:LINKED]->(m)-[:LINKED]->(n)-[:LINKED]->(m)""").consume();
+	}
+
 	@BeforeEach
 	protected void prepareIndividual(
 			@Autowired CityModelRepository cityModelRepository
@@ -907,6 +927,15 @@ void unwindWithMergeShouldWork(@Autowired Neo4jTemplate template, @Autowired Tab
 				});
 	}
 
+	@Test
+	@Tag("GH-2583")
+	void mapStandardCustomQueryWithLotsOfRelationshipsProperly(@Autowired GH2583Repository repository) {
+		Page<GH2583Node> nodePage = repository.getNodesByCustomQuery(PageRequest.of(0, 300));
+
+		List<GH2583Node> nodes = nodePage.getContent();
+		assertThat(nodes).hasSize(2);
+	}
+
 	@Configuration
 	@EnableTransactionManagement
 	@EnableNeo4jRepositories(namedQueriesLocation = "more-custom-queries.properties")

src/test/java/org/springframework/data/neo4j/integration/issues/gh2583/GH2583Node.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2011-2022 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
+ *
+ *      https://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.neo4j.integration.issues.gh2583;
+
+import org.springframework.data.neo4j.core.schema.GeneratedValue;
+import org.springframework.data.neo4j.core.schema.Id;
+import org.springframework.data.neo4j.core.schema.Node;
+import org.springframework.data.neo4j.core.schema.Relationship;
+
+import java.util.List;
+
+/**
+ * A simple node with bidirectional relationship mapping to the very same type.
+ */
+@Node
+public class GH2583Node {
+	@Id
+	@GeneratedValue
+	Long id;
+
+	@Relationship(type = "LINKED", direction = Relationship.Direction.OUTGOING)
+	public List<GH2583Node> outgoingNodes;
+
+	@Relationship(type = "LINKED", direction = Relationship.Direction.INCOMING)
+	public List<GH2583Node> incomingNodes;
+}

src/test/java/org/springframework/data/neo4j/integration/issues/gh2583/GH2583Repository.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2011-2022 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
+ *
+ *      https://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.neo4j.integration.issues.gh2583;
+
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.neo4j.repository.Neo4jRepository;
+import org.springframework.data.neo4j.repository.query.Query;
+
+/**
+ * Repository with custom query that uncovers a possible StackOverflowError.
+ */
+public interface GH2583Repository extends Neo4jRepository<GH2583Node, Long> {
+
+	@Query(value = "MATCH (s:GH2583Node) " +
+			"WITH s OPTIONAL MATCH (s)-[r:LINKED]->(t:GH2583Node) " +
+			"RETURN s, collect(r), collect(t) " +
+			":#{orderBy(#pageable)} SKIP $skip LIMIT $limit",
+			countQuery = "MATCH (s:hktxjm) RETURN count(s)")
+	Page<GH2583Node> getNodesByCustomQuery(Pageable pageable);
+}