Add validation to ToUndirected to make sure relationship type is not already undirected

Author: DarthMax

proc/beta/src/main/java/org/neo4j/gds/beta/undirected/ToUndirectedSpec.java

@@ -21,6 +21,7 @@
 
 import org.neo4j.gds.MutateComputationResultConsumer;
 import org.neo4j.gds.RelationshipType;
+import org.neo4j.gds.api.schema.Direction;
 import org.neo4j.gds.config.ElementTypeValidator;
 import org.neo4j.gds.core.loading.SingleTypeRelationshipImportResult;
 import org.neo4j.gds.executor.AlgorithmSpec;
@@ -36,6 +37,7 @@
 import org.neo4j.gds.results.StandardMutateResult;
 
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.stream.Stream;
 
@@ -93,6 +95,21 @@ public List<AfterLoadValidation<ToUndirectedConfig>> afterLoadValidations() {
                     (graphStore, graphProjectConfig, config) -> {
                         var relationshipType = RelationshipType.of(config.relationshipType());
                         ElementTypeValidator.validateTypes(graphStore, List.of(relationshipType), "`relationshipType`");
+                    },
+                    (graphStore, graphProjectConfig, config) -> {
+                        var relationshipType = RelationshipType.of(config.relationshipType());
+                        Direction direction = graphStore
+                            .schema()
+                            .relationshipSchema()
+                            .get(relationshipType)
+                            .direction();
+                        if (direction == Direction.UNDIRECTED) {
+                            throw new UnsupportedOperationException(String.format(
+                                Locale.US,
+                                "The specified relationship type `%s` is already undirected.",
+                                relationshipType.name
+                            ));
+                        }
                     }
                 );
             }

proc/beta/src/test/java/org/neo4j/gds/beta/undirected/ToUndirectedProcTest.java

@@ -46,7 +46,7 @@ class ToUndirectedProcTest extends BaseProcTest {
 
     @Neo4jGraph
     public static final String DB = "CREATE " +
-                                    "(a:A) " +
+                                    " (a:A) " +
                                     ",(b:B) " +
                                     ",(c:C) " +
                                     ",(a)-[:REL {prop1: 1.0}]->(b)" +
@@ -66,6 +66,16 @@ void setup() throws Exception {
             .withRelationshipProperty("prop1")
             .yields()
         );
+
+        runQuery(GdsCypher.call("undirected_graph")
+            .graphProject()
+            .withNodeLabel("A")
+            .withNodeLabel("B")
+            .withNodeLabel("C")
+            .withRelationshipType("REL", Orientation.UNDIRECTED)
+            .withRelationshipProperty("prop1")
+            .yields()
+        );
     }
 
     @Test
@@ -113,6 +123,15 @@ void shouldFailIfRelationshipTypeDoesNotExists() {
         assertEquals(expectedMessage, throwable.getMessage());
     }
 
+    @Test
+    void shouldFailIfRelationshipTypeIsAlreadyUndirected() {
+        String query = "CALL gds.beta.graph.relationships.toUndirected('undirected_graph', {relationshipType: 'REL', mutateRelationshipType: 'REL2'})";
+
+        Throwable throwable = rootCause(assertThrows(QueryExecutionException.class, () -> runQuery(query)));
+        assertEquals(UnsupportedOperationException.class, throwable.getClass());
+        assertEquals("The specified relationship type `REL` is already undirected.", throwable.getMessage());
+    }
+
     @Test
     void memoryEstimation() {
         String query = "CALL gds.beta.graph.relationships.toUndirected.estimate('graph', {relationshipType: 'REL', mutateRelationshipType: 'REL2'})";