Refactor service and controller to handle Optional returns

- Refactor `DashboardDrawerService` methods to return `Optional`
- Update controller methods to handle `Optional` results with appropriate HTTP responses
- Modify repository methods to return `Optional` for single item queries
- Ensure consistency and error handling improvements across the service and controller layers

src/main/java/edu/harvard/dbmi/avillach/dictionary/dashboarddrawer/DashboardDrawerController.java

@@ -14,11 +14,11 @@ public class DashboardDrawerController {
 
     @GetMapping
     public ResponseEntity<DashboardDrawerList> findAll() {
-        return ResponseEntity.ok(dashboardDrawerService.findAll());
+        return dashboardDrawerService.findAll().map(ResponseEntity::ok).orElseGet(() -> ResponseEntity.notFound().build());
     }
 
     @GetMapping("/{id}")
     public ResponseEntity<DashboardDrawer> findByDatasetId(@PathVariable Integer id) {
-        return ResponseEntity.ok(dashboardDrawerService.findByDatasetId(id));
+        return dashboardDrawerService.findByDatasetId(id).map(ResponseEntity::ok).orElseGet(() -> ResponseEntity.notFound().build());
     }
 }

src/main/java/edu/harvard/dbmi/avillach/dictionary/dashboarddrawer/DashboardDrawerRepository.java

@@ -49,7 +49,7 @@ public List<DashboardDrawer> getDashboardDrawerRows() {
         }
     }
 
-    public List<DashboardDrawer> getDashboardDrawerRows(Integer datasetId) {
+    public Optional<DashboardDrawer> getDashboardDrawerRows(Integer datasetId) {
         String materializedViewSql = """
             select * from dictionary_db.dict.dataset_meta_materialized_view dmmv where dmmv.dataset_id = :datasetId;
             """;
@@ -73,10 +73,10 @@ public List<DashboardDrawer> getDashboardDrawerRows(Integer datasetId) {
         params.addValue("datasetId", datasetId);
 
         try {
-            return template.query(materializedViewSql, params, new DashboardDrawerRowMapper());
+            return template.query(materializedViewSql, params, new DashboardDrawerRowMapper()).stream().findFirst();
         } catch (Exception e) {
             log.debug("Materialized view not available, using fallback query. Error: {}", e.getMessage());
-            return template.query(fallbackSql, params, new DashboardDrawerRowMapper());
+            return template.query(fallbackSql, params, new DashboardDrawerRowMapper()).stream().findFirst();
         }
     }
 }

src/main/java/edu/harvard/dbmi/avillach/dictionary/dashboarddrawer/DashboardDrawerService.java

@@ -6,6 +6,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Optional;
 
 @Service
 public class DashboardDrawerService {
@@ -24,13 +25,13 @@ public DashboardDrawerService(DashboardDrawerRepository repository, @Value("${da
      *
      * @return All Dashboard Instances and their metadata.
      */
-    public DashboardDrawerList findAll() {
+    public Optional<DashboardDrawerList> findAll() {
         if (dashboardLayout.equalsIgnoreCase("bdc")) {
             List<DashboardDrawer> records = repository.getDashboardDrawerRows();
-            return new DashboardDrawerList(records);
+            return Optional.of(new DashboardDrawerList(records));
         }
 
-        return new DashboardDrawerList(new ArrayList<>());
+        return Optional.of(new DashboardDrawerList(new ArrayList<>()));
     }
 
     /**
@@ -40,15 +41,10 @@ public DashboardDrawerList findAll() {
      * @param datasetId the ID of the dataset to fetch.
      * @return a single Dashboard instance with drawer-specific metadata.
      */
-    public DashboardDrawer findByDatasetId(Integer datasetId) {
-        if (dashboardLayout.equalsIgnoreCase("bdc")) {
-            List<DashboardDrawer> records = repository.getDashboardDrawerRows(datasetId);
-
-            if (records.size() == 1) {
-                return records.getFirst();
-            }
+    public Optional<DashboardDrawer> findByDatasetId(Integer datasetId) {
+        if ("bdc".equalsIgnoreCase(dashboardLayout)) {
+            return repository.getDashboardDrawerRows(datasetId);
         }
-
-        return new DashboardDrawer(-1, "", "", new ArrayList<>(), "", new ArrayList<>(), "", "");
+        return Optional.empty();
     }
 }