[NOID] Return a node even if no relationships exist (#4168)

Author: gem-neo4j

core/src/main/java/apoc/convert/Json.java

@@ -234,7 +234,6 @@ public Stream<MapResult> toTree(
     @Procedure("apoc.paths.toJsonTree")
     @Description(
             "apoc.paths.toJsonTree([paths],[lowerCaseRels=true], [config]) creates a stream of nested documents representing the graph as a tree by traversing outgoing relationships")
-    // todo optinally provide root node
     public Stream<MapResult> pathsToTree(
             @Name("paths") List<Path> paths,
             @Name(value = "lowerCaseRels", defaultValue = "true") boolean lowerCaseRels,
@@ -254,6 +253,16 @@ public Stream<MapResult> pathsToTree(
         allPaths.forEach(path -> {
             // This api will always return relationships in an outgoing fashion ()-[r]->()
             var pathRelationships = path.relationships();
+            // If no relationships exist in the path, then add the node by itself
+            if (!pathRelationships.iterator().hasNext()) {
+                Node currentNode = path.startNode();
+                Long currentNodeId = currentNode.getId();
+
+                if (!visitedInOtherPaths.contains(currentNodeId)) {
+                    nodesToKeepInResult.add(currentNodeId);
+                }
+                tree.computeIfAbsent(currentNode.getId(), (id) -> toMap(currentNode, nodes));
+            }
             pathRelationships.iterator().forEachRemaining((currentRel) -> {
                 Node currentNode = currentRel.getStartNode();
                 Long currentNodeId = currentNode.getId();

core/src/test/java/apoc/convert/PathsToJsonTreeTest.java

@@ -56,7 +56,7 @@ public void clear() {
     }
 
     @Test
-    public void testToTreeSimplePath() throws Exception {
+    public void testToTreeSimplePath() {
         /*            r:R
               a:A --------> b:B
         */
@@ -90,6 +90,68 @@ public void testToTreeSimplePath() throws Exception {
         }
     }
 
+    @Test
+    public void testSingleNode() {
+        // a:A
+        db.executeTransactionally("CREATE (a: A {nodeName: 'a'})");
+
+        var query = "MATCH path = (n)\n"
+                + "WITH COLLECT(path) AS paths\n"
+                + "CALL apoc.paths.toJsonTree(paths, true, {sortPaths: false}) YIELD value AS tree\n"
+                + "RETURN tree";
+
+        try (Transaction tx = db.beginTx()) {
+            Result result = tx.execute(query);
+            var rows = result.stream().collect(Collectors.toList());
+            var expectedRow = "{" + "   \"tree\":{"
+                    + "      \"nodeName\":\"a\","
+                    + "      \"_type\":\"A\","
+                    + "      \"_id\":0"
+                    + "   }"
+                    + "}";
+            assertEquals(rows.size(), 1);
+            assertEquals(parseJson(expectedRow), rows.get(0));
+        }
+    }
+
+    @Test
+    public void testSingleDisjointNodes() {
+        // a:A
+        db.executeTransactionally("CREATE (a: A {nodeName: 'a'}), (b: B {nodeName: 'b'}), (c: C {nodeName: 'c'})");
+
+        var query = "MATCH path = (n)\n"
+                + "WITH COLLECT(path) AS paths\n"
+                + "CALL apoc.paths.toJsonTree(paths, true, {sortPaths: false}) YIELD value AS tree\n"
+                + "RETURN tree";
+
+        try (Transaction tx = db.beginTx()) {
+            Result result = tx.execute(query);
+            var rows = result.stream().collect(Collectors.toList());
+            var expectedRowA = "{" + "   \"tree\":{"
+                    + "      \"nodeName\":\"a\","
+                    + "      \"_type\":\"A\","
+                    + "      \"_id\":0"
+                    + "   }"
+                    + "}";
+            var expectedRowB = "{" + "   \"tree\":{"
+                    + "      \"nodeName\":\"b\","
+                    + "      \"_type\":\"B\","
+                    + "      \"_id\":1"
+                    + "   }"
+                    + "}";
+            var expectedRowC = "{" + "   \"tree\":{"
+                    + "      \"nodeName\":\"c\","
+                    + "      \"_type\":\"C\","
+                    + "      \"_id\":2"
+                    + "   }"
+                    + "}";
+            assertEquals(rows.size(), 3);
+            assertEquals(parseJson(expectedRowA), rows.get(0));
+            assertEquals(parseJson(expectedRowB), rows.get(1));
+            assertEquals(parseJson(expectedRowC), rows.get(2));
+        }
+    }
+
     @Test
     public void testToTreeSimpleReversePath() {
         /*            r:R