implement

dotnet/AipsCore/Domain/Models/Whiteboard/Validation/WhiteboardErrors.cs

@@ -0,0 +1,18 @@
+using AipsCore.Domain.Abstract.Validation;
+using AipsCore.Domain.Common.Validation;
+using AipsCore.Domain.Models.User.ValueObjects;
+using AipsCore.Domain.Models.Whiteboard.ValueObjects;
+
+namespace AipsCore.Domain.Models.Whiteboard.Validation;
+
+public class WhiteboardErrors : AbstractErrors<Whiteboard, WhiteboardId>
+{
+    public static ValidationError UserAlreadyAdded(UserId userId)
+    {
+        string code = "user_already_added";
+        string message = $"User with id '{userId}' already added to this whiteboard";
+
+        return CreateValidationError(code, message);
+    }
+        
+}