Index: kernel/include/IMP/decorators/HierarchyDecorator.h
===================================================================
--- kernel/include/IMP/decorators/HierarchyDecorator.h	(revision 514)
+++ kernel/include/IMP/decorators/HierarchyDecorator.h	(working copy)
@@ -50,9 +50,9 @@
 class IMPDLLEXPORT HierarchyDecorator: public DecoratorBase
 {
   IMP_DECORATOR(HierarchyDecorator, DecoratorBase, return true || p,  ++p);
-  IMP_DECORATOR_ARRAY_DECL(child, Int)
+  IMP_DECORATOR_ARRAY_DECL(child, Particle, Particle*, NULL)
 protected:
-  static IntKey parent_key_;
+  static ParticleKey parent_key_;
   static IntKey parent_index_key_;
 
 public:
@@ -62,14 +62,14 @@
       if it has no parent.
    */
   This get_parent() const {
-    IMP_DECORATOR_GET(parent_key_, Int,
-                      return cast(get_model()->
-                                  get_particle(ParticleIndex(VALUE))),
+    IMP_DECORATOR_GET(parent_key_, Particle*,
+                      return VALUE,
                       return This());
   }
 
   //! Get the number of children.
   unsigned int get_number_of_children() const {
+    // defined by the array macro
     return internal_get_number_of_child();
   }
 
@@ -78,8 +78,8 @@
       does not have this child
    */
   This get_child(unsigned int i) const {
-    return cast(get_model()->
-                get_particle(ParticleIndex(internal_get_child(i))));
+    // defined by the array macro
+    return cast(internal_get_child(i));
 
   }
 
Index: kernel/src/decorators/HierarchyDecorator.cpp
===================================================================
--- kernel/src/decorators/HierarchyDecorator.cpp	(revision 514)
+++ kernel/src/decorators/HierarchyDecorator.cpp	(working copy)
@@ -14,8 +14,8 @@
 namespace IMP
 {
 
-IMP_DECORATOR_ARRAY_DEF(Hierarchy, child, Int);
-IntKey HierarchyDecorator::parent_key_;
+IMP_DECORATOR_ARRAY_DEF(Hierarchy, child, Particle, Particle*);
+ParticleKey HierarchyDecorator::parent_key_;
 IntKey HierarchyDecorator::parent_index_key_;
 
 
@@ -101,12 +101,10 @@
   //std::cerr << "changing " << std::endl;
   //std::cerr << "before\n";
   //show_hierarchy<NameDecorator>(*this, std::cerr);
-  int pi= get_particle()->get_index().get_index();
-  int ci= hd.get_particle()->get_index().get_index();
-  int nc= internal_add_child(ci);
+  int nc= internal_add_child(hd.get_particle());
 
   hd.get_particle()->add_attribute(parent_index_key_, nc);
-  hd.get_particle()->add_attribute(parent_key_, pi);
+  hd.get_particle()->add_attribute(parent_key_, get_particle());
   //std::cerr << "after\n";
   //show_hierarchy<NameDecorator>(*this, std::cerr);
   return nc;
@@ -115,10 +113,10 @@
 
 IMP_DECORATOR_INITIALIZE(HierarchyDecorator, DecoratorBase,
                          {
-                           parent_key_ = IntKey("hierarchy_parent");
+                           parent_key_ = ParticleKey("hierarchy_parent");
                            parent_index_key_ = IntKey("hiearchy_parent_index");
                            IMP_DECORATOR_ARRAY_INIT(HierarchyDecorator,
-                                                    child, Int);
+                                                    child, Particle, Particle*);
                          })