BlazorEditForms/Model/Aggregate.cs

using FluentValidation;

namespace BlazorEditForms.Model;

public class Aggregate
{
    public Aggregate(Employee employee, User? user)
    {
        Employee = employee;
        User = user;
    }

    public Employee Employee { get; set; }
    public User? User { get; set; }
}

public class AggregateValidator : AbstractValidator<Aggregate>
{
    public AggregateValidator()
    {
        RuleFor(x => x.Employee).NotNull().SetValidator(new EmployeeValidator());
        When(x => x.User != null, () => RuleFor(x => x.User!).SetValidator(new UserValidator()));
    }
}