Fix #28: Add JSON payload builder for DetClassification + preferred_name alias fix

lib/opencdd/exporters/json.rb

@@ -70,14 +70,15 @@ def visit_list_of_unit(lou)
       # omitted (payload still has all the entity's own fields).
       # ─────────────────────────────────────────────────────────────
       PAYLOAD_BUILDERS = {
-        Opencdd::Klass        => :class_node,
-        Opencdd::Property     => :property_node,
-        Opencdd::Unit         => :unit_node,
-        Opencdd::ValueList    => :value_list_node,
-        Opencdd::ValueTerm    => :value_term_node,
-        Opencdd::Relation     => :relation_node,
-        Opencdd::ViewControl  => :view_control_node,
-        Opencdd::ListUnit     => :list_of_unit_node,
+        Opencdd::Klass             => :class_node,
+        Opencdd::Property          => :property_node,
+        Opencdd::Unit              => :unit_node,
+        Opencdd::ValueList         => :value_list_node,
+        Opencdd::ValueTerm         => :value_term_node,
+        Opencdd::Relation          => :relation_node,
+        Opencdd::ViewControl       => :view_control_node,
+        Opencdd::ListUnit          => :list_of_unit_node,
+        Opencdd::DetClassification => :det_classification_node,
       }.freeze
 
       def payload_for(entity, database: nil)
@@ -134,6 +135,10 @@ def list_of_unit_node(lou)
         entity_payload(lou).merge(type: "list_of_unit").compact
       end
 
+      def det_classification_node(det)
+        entity_payload(det).merge(type: "det_classification").compact
+      end
+
       private
 
       # Iterates every declared field on the entity's class (walking

lib/opencdd/parcel/sheet_schema.rb

@@ -27,13 +27,16 @@ class SheetSchema
         # project-specific column IDs (C0001 = code, C0002.<lang> = name)
         # rather than the standard MDC codes. Without these mappings,
         # every DET classification entity would have nil code + name.
+        #
+        # C0002 maps to MDC_P004 (preferred_name), not MDC_P004_1
+        # (preferred_name_localized), because canonical_id splits the
+        # language suffix off and reapplies it after the base lookup —
+        # so the per-language entries (C0002.en, C0002.fr, etc.) below
+        # would be dead code. The base entry alone produces
+        # MDC_P004.<lang>, which is what the preferred_name field DSL
+        # reads via FieldRegistry.
         "IECCDD_001_C0001"     => "MDC_P001_5",
-        "IECCDD_001_C0002"     => "MDC_P004_1",
-        "IECCDD_001_C0002.en"   => "MDC_P004_1.en",
-        "IECCDD_001_C0002.fr"   => "MDC_P004_1.fr",
-        "IECCDD_001_C0002.de"   => "MDC_P004_1.de",
-        "IECCDD_001_C0002.ja"   => "MDC_P004_1.ja",
-        "IECCDD_001_C0002.zh"   => "MDC_P004_1.zh",
+        "IECCDD_001_C0002"     => "MDC_P004",
       }.freeze
 
       # Canonicalize a Parcel column ID. Splits language tags

spec/exporters/per_entity_json_spec.rb

@@ -52,6 +52,28 @@
       it { is_expected.to include(type: "value_list") }
     end
 
+    context "with a det_classification entity" do
+      let(:entity) do
+        Opencdd::DetClassification.new(
+          irdi: Opencdd::IRDI.parse("0112/2///IECCDD_001#A11"),
+          properties: {
+            "MDC_P001_5" => "A11",
+            "MDC_P004.en" => "geographical unit (greater than a place)",
+          },
+          meta_class_irdi: Opencdd::IRDI.parse("MDC_C0101"),
+        )
+      end
+      subject(:payload) { exporter.payload_for(entity) }
+
+      it { is_expected.to include(type: "det_classification") }
+      it { is_expected.to include(irdi: "0112/2///IECCDD_001#A11") }
+      it { is_expected.to include(code: "A11") }
+
+      it "includes the preferred name" do
+        expect(payload["preferred_name"]).to eq("geographical unit (greater than a place)")
+      end
+    end
+
     context "without a database (no cross-link resolution)" do
       let(:entity) { database.properties.first }
       subject(:payload) { exporter.payload_for(entity) }