public IEnumerable<ValidationResult> Validate(ValidationContext validationContext) { var dbMan = new DataBaseManager(); if (dbMan.User.Get(Name) != null) yield return new ValidationResult("This name has already been taken", new[] { "Name" }); if (dbMan.User.GetAll().Any(u => u.Email == Email)) yield return new ValidationResult("This email is already registered", new[] { "Email" }); }