added validators in project

BookHive/Validators/Books/GetBookDtoValidator.cs

@@ -0,0 +1,28 @@
+using BookHive.DTO.Book;
+using FastEndpoints;
+using FluentValidation;
+
+namespace BookHive.Validators.Books;
+
+public class GetBookDtoValidator : Validator<GetBookDto>
+{
+    public GetBookDtoValidator()
+    {
+        RuleFor(x => x.Id)
+            .GreaterThan(0)
+            .WithMessage("Id is invalid");
+
+        RuleFor(x => x.Title)
+            .NotEmpty()
+            .WithMessage("Title is required");
+        
+        RuleFor(x => x.Isbn)
+            .NotEmpty().WithMessage("L’ISBN est obligatoire.")
+            .Matches(@"^\d{13}$")
+            .WithMessage("L’ISBN doit contenir exactement 13 chiffres.");
+        
+        RuleFor(x => x.AuthorFullName)
+            .NotEmpty()
+            .WithMessage("AuthorFullName is required");
+    }
+}