diff --git a/src/ifcparse/IfcEntityInstanceData.cpp b/src/ifcparse/IfcEntityInstanceData.cpp
index 14e5864d9c..0c79314327 100644
--- a/src/ifcparse/IfcEntityInstanceData.cpp
+++ b/src/ifcparse/IfcEntityInstanceData.cpp
@@ -350,6 +350,26 @@ bool impl::deserialize(IfcParse::impl::rocks_db_file_storage*, const std::string
     return false;
 }
 
+template<typename T>
+bool rocks_db_attribute_storage::has(void* storage, const IfcParse::declaration* decl, std::size_t identity, std::size_t index) const
+{
+    // @todo unify with other implementation functions
+    const bool is_header = decl->schema() == &Header_section_schema::get_schema();
+    IfcParse::impl::rocks_db_file_storage* rdb_storage = (IfcParse::impl::rocks_db_file_storage*)storage;
+    std::string v;
+    auto success = rdb_storage->db->Get(
+        rocksdb::ReadOptions{},
+        (is_header ? "h|" : (decl->as_entity() ? "i|" : "t|")) +
+        (is_header ? decl->name() : std::to_string(identity)) + "|" +
+        std::to_string(index), &v);
+    if constexpr (std::is_same_v<std::decay_t<T>, Blank>) {
+        if (!success.ok()) {
+            return true;
+        }
+    }
+    return v.size() && v[0] == TypeEncoder::encode_type<T>();
+}
+
 template<typename T>
 void rocks_db_attribute_storage::set(void* storage, const IfcParse::declaration* decl, std::size_t identity, std::size_t index, const T& value)
 {
@@ -386,3 +406,28 @@ template void rocks_db_attribute_storage::set<aggregate_of_aggregate_of_instance
 template void rocks_db_attribute_storage::set<Derived>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index, const Derived& value);
 template void rocks_db_attribute_storage::set<empty_aggregate_t>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index, const empty_aggregate_t& value);
 template void rocks_db_attribute_storage::set<empty_aggregate_of_aggregate_t>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index, const empty_aggregate_of_aggregate_t& value);
+
+
+
+template bool rocks_db_attribute_storage::has<Blank>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<int>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<bool>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<boost::logic::tribool>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<double>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<std::string>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<boost::dynamic_bitset<>>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<EnumerationReference>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<IfcUtil::IfcBaseClass*>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<std::vector<int>>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<std::vector<double>>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<std::vector<std::string>>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<std::vector<boost::dynamic_bitset<>>>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<aggregate_of_instance::ptr>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<std::vector<std::vector<int>>>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<std::vector<std::vector<double>>>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<aggregate_of_aggregate_of_instance::ptr>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+
+// @todo why do these need to be included, but are not in BaseEntity::set()?
+template bool rocks_db_attribute_storage::has<Derived>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<empty_aggregate_t>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
+template bool rocks_db_attribute_storage::has<empty_aggregate_of_aggregate_t>(void* storage, const IfcParse::declaration* decl, std::size_t identity, size_t index) const;
diff --git a/src/ifcparse/IfcEntityInstanceData.h b/src/ifcparse/IfcEntityInstanceData.h
index 92e006fef2..cfcb466af5 100644
--- a/src/ifcparse/IfcEntityInstanceData.h
+++ b/src/ifcparse/IfcEntityInstanceData.h
@@ -385,17 +385,6 @@ struct AttributeValue {
 };
 
 struct rocks_db_attribute_storage {
-private:
-    template<typename Visitor, std::size_t Index>
-    auto apply_visitor_impl(Visitor&& visitor, std::size_t idx, std::integral_constant<std::size_t, Index>) const {
-        return apply_visitor_impl(std::forward<Visitor>(visitor), idx, std::integral_constant<std::size_t, Index - 1>{});
-    }
-
-    template<typename Visitor>
-    void apply_visitor_impl(Visitor&&, std::size_t, std::integral_constant<std::size_t, 0>) const {
-        throw std::runtime_error("Invalid variant index");
-    }
-
 public:
     size_t size(void*, const IfcParse::declaration*, std::size_t identity) const {
         // @todo is this actually needed?
@@ -407,14 +396,12 @@ public:
     void set(void* storage, const IfcParse::declaration*, std::size_t identity, std::size_t index, const T& value);
 
     template<typename T>
-    bool has(void* storage, const IfcParse::declaration*, std::size_t identity, std::size_t index) const {
-        // @todo
-        return false;
-    }
+    bool has(void* storage, const IfcParse::declaration* decl, std::size_t identity, std::size_t index) const;
 
     template<typename Visitor>
-    auto apply_visitor(void* storage, const IfcParse::declaration*, std::size_t identity, std::size_t index, Visitor&& visitor) const {
-        return apply_visitor_impl(std::forward<Visitor>(visitor), index, std::integral_constant<std::size_t, type_variant_parameter_pack::size>{});
+    auto apply_visitor(void* storage, const IfcParse::declaration* decl, std::size_t identity, std::size_t index, Visitor&& visitor) const {
+        // @todo do we need visitation on all data/storage/attribute levels?
+        AttributeValue((IfcParse::impl::rocks_db_file_storage*)storage, identity, decl->as_entity() ? 1 : 0, index).apply_visitor(std::forward<Visitor>(visitor));
     }
 };