Functionality done

buisnesslogic/src/main/java/com/plannaplan/services/GroupService.java

@@ -41,4 +41,15 @@ public class GroupService {
     public Optional<Groups> getGroupById(Long id) {
         return this.repo.findById(id);
     }
+
+    public Long findNotExistingGroup(List<Long> ids) {
+        Long response = Long.MIN_VALUE;
+        for (Long oneId : ids) {
+            if (this.repo.existsById(oneId) == false) {
+                response = oneId;
+            }
+        }
+        return response;
+
+    }
 }

buisnesslogic/src/main/java/com/plannaplan/services/UserService.java

@@ -49,4 +49,8 @@ public class UserService {
         return this.repo.searchForUsers(query, UserRoles.STUDENT);
     }
 
+    public Optional<User> getById(Long userId) {
+        return this.repo.findById(userId);
+    }
+
 }