fix nested structure serialization for referenceable/struct

repository/src/test/java/org/apache/hadoop/metadata/repository/memory/InstanceE2ETest.java

@@ -152,7 +152,6 @@ public class InstanceE2ETest extends BaseTest {
         Referenceable  r1 = InstanceSerialization$.MODULE$.fromJsonReferenceable(jsonStr, true);
         ClassType tableType = ts.getDataType(ClassType.class, "hive_table");
 
-        /* todo: fix deserialization, so following conver works
         ITypedReferenceableInstance i = tableType.convert(r1, Multiplicity.REQUIRED);
 
         jsonStr = Serialization$.MODULE$.toJson(i);
@@ -160,6 +159,6 @@ public class InstanceE2ETest extends BaseTest {
 
         i = Serialization$.MODULE$.fromJson(jsonStr);
         System.out.println(i);
-        */
+
     }
 }

typesystem/src/main/scala/org/apache/hadoop/metadata/typesystem/json/Serialization.scala

@@ -347,7 +347,7 @@ object InstanceSerialization {
 
   val _formats = new DefaultFormats {
     override val dateFormatter = TypeSystem.getInstance().getDateFormat.asInstanceOf[SimpleDateFormat]
-    override val typeHints = NoTypeHints
+    override val typeHints = FullTypeHints(List(classOf[_Id], classOf[_Struct], classOf[_Reference]))
   }
 
   def buildFormat(withBigDecimals : Boolean) = {