added validators in project

BookHive/Validators/Loans/UpdateLoanDtoValidator.cs

@@ -0,0 +1,42 @@
+using BookHive.DTO.Loan;
+using FastEndpoints;
+using FluentValidation;
+
+namespace BookHive.Validators.Loans;
+
+public class UpdateLoanDtoValidator : Validator<UpdateLoanDto>
+{
+    public UpdateLoanDtoValidator()
+    {
+        RuleFor(x => x.Id)
+            .GreaterThan(0)
+            .WithMessage("Id is invalid.");
+        
+        RuleFor(x => x.BookId)
+            .GreaterThan(0)
+            .WithMessage("Invalid book id.");
+        
+        RuleFor(x => x.MemberId)
+            .GreaterThan(0)
+            .WithMessage("Invalid member id.");
+        
+        RuleFor(x => x.LoanDate)
+            .NotEmpty()
+            .WithMessage("Date is required.");
+        
+        RuleFor(x => x.DueDate)
+            .NotEmpty()
+            .WithMessage("Due date is required.")
+            .GreaterThan(d => d.LoanDate)
+            .WithMessage("Due date must be in the future.")
+            .Must((loan, dueDate) => dueDate <= loan.LoanDate.AddDays(30))
+            .WithMessage("Due date must be in the future.");
+
+        When(x => x.ReturnDate != null, () =>
+        {
+            RuleFor(x => x.ReturnDate)
+                .GreaterThan(d => d.LoanDate)
+                .WithMessage("Return date must be in the future.");
+        });
+    }
+}