Add allocation variety change history UI

backend/apps/plans/serializers.py

@@ -35,6 +35,8 @@ class PlanSerializer(serializers.ModelSerializer):
     crop_name = serializers.ReadOnlyField(source='crop.name')
     variety_name = serializers.ReadOnlyField(source='variety.name')
     field_name = serializers.ReadOnlyField(source='field.name')
+    variety_change_count = serializers.SerializerMethodField()
+    latest_variety_change = serializers.SerializerMethodField()
 
     class Meta:
         model = Plan
@@ -52,6 +54,32 @@ class PlanSerializer(serializers.ModelSerializer):
             notes=validated_data.get('notes', NO_CHANGE),
         )
 
+    def get_variety_change_count(self, obj):
+        prefetched = getattr(obj, '_prefetched_objects_cache', {})
+        changes = prefetched.get('variety_changes')
+        if changes is not None:
+            return len(changes)
+        return obj.variety_changes.count()
+
+    def get_latest_variety_change(self, obj):
+        prefetched = getattr(obj, '_prefetched_objects_cache', {})
+        changes = prefetched.get('variety_changes')
+        if changes is not None:
+            latest = changes[0] if changes else None
+        else:
+            latest = obj.variety_changes.select_related('old_variety', 'new_variety').first()
+        if latest is None:
+            return None
+        return {
+            'id': latest.id,
+            'changed_at': latest.changed_at,
+            'old_variety_id': latest.old_variety_id,
+            'old_variety_name': latest.old_variety.name if latest.old_variety else None,
+            'new_variety_id': latest.new_variety_id,
+            'new_variety_name': latest.new_variety.name if latest.new_variety else None,
+            'fertilizer_moved_entry_count': latest.fertilizer_moved_entry_count,
+        }
+
 
 class RiceTransplantEntrySerializer(serializers.ModelSerializer):
     field_name = serializers.CharField(source='field.name', read_only=True)