refactor: simplify code - extract constants, reduce complexity

backend/src/v1/schedule_items/service.py

@@ -112,26 +112,16 @@ class ScheduleItemService(BaseService):
             if existing is None:
                 raise HTTPException(status_code=404, detail="Schedule item not found")
 
-            update_data: dict = {}
-            if request.title is not None:
-                update_data["title"] = request.title
-            if request.description is not None:
-                update_data["description"] = request.description
-            if request.start_at is not None:
-                update_data["start_at"] = request.start_at
-            if request.end_at is not None:
-                update_data["end_at"] = request.end_at
-            if request.timezone is not None:
-                update_data["timezone"] = request.timezone
-            if request.status is not None:
-                update_data["status"] = request.status
-            if request.metadata is not None:
-                update_data["metadata"] = request.metadata.model_dump()
+            # Build update dict from non-null fields
+            update_data = request.model_dump(exclude_unset=True)
 
-            next_start = (
-                request.start_at if request.start_at is not None else existing.start_at
-            )
-            next_end = request.end_at if request.end_at is not None else existing.end_at
+            # Handle metadata separately (model_dump returns dict)
+            if "metadata" in update_data and update_data["metadata"] is not None:
+                update_data["metadata"] = update_data["metadata"].model_dump()
+
+            # Validate time range
+            next_start = update_data.get("start_at", existing.start_at)
+            next_end = update_data.get("end_at", existing.end_at)
             if next_end is not None and next_end <= next_start:
                 raise HTTPException(
                     status_code=400, detail="end_at must be after start_at"