Working on users view, added infrastructure lib

UserService.Infrastructure/Validators.cs

@@ -0,0 +1,22 @@
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+using UserService.Infrastructure.DataModels;
+
+namespace UserService.Infrastructure
+{
+    public static class Validators
+    {
+        public static bool? ValidateEmail(string mailAddress)
+        {
+            if (string.IsNullOrEmpty(mailAddress)) return null;
+            return new EmailAddressAttribute().IsValid(mailAddress);
+        }
+
+        public static bool? ValidateCommonName(string commonName, IReadOnlyList<User> users)
+        {
+            if (string.IsNullOrEmpty(commonName)) return false;
+            return users.All(x => x.CommonName != commonName);
+        }
+    }
+}