[~] allow ordering list properties via index

Author: pm-osc

janusgraph-core/src/main/java/org/janusgraph/graphdb/query/graph/GraphCentricQueryBuilder.java

@@ -201,9 +201,6 @@ public GraphCentricQueryBuilder orderBy(String keyName,  org.apache.tinkerpop.gr
         Preconditions.checkArgument(key!=null && order!=null,"Need to specify and key and an order");
         Preconditions.checkArgument(Comparable.class.isAssignableFrom(key.dataType()),
                 "Can only order on keys with comparable data type. [%s] has datatype [%s]", key.name(), key.dataType());
-        // TODO: test commit
-        Preconditions.checkArgument(key.cardinality()== Cardinality.SINGLE,
-                "Ordering is undefined on multi-valued key [%s]", key.name());
         Preconditions.checkArgument(!orders.containsKey(key), "orders [%s] already contains key [%s]", orders, key);
         orders.add(key, Order.convert(order));
         return this;

janusgraph-core/src/main/java/org/janusgraph/graphdb/tinkerpop/optimize/step/HasStepFolder.java

@@ -121,8 +121,7 @@ static boolean validJanusGraphOrder(OrderGlobalStep orderGlobalStep, Traversal r
             final PropertyKey pKey = tx.getPropertyKey(key);
             // TODO: test commit
             if (pKey == null
-                || !(Comparable.class.isAssignableFrom(pKey.dataType()))
-                || (isVertexOrder && pKey.cardinality() != Cardinality.SINGLE)) {
+                || !(Comparable.class.isAssignableFrom(pKey.dataType()))) {
                 return false;
             }
         }