private void DoSave(Action onSuccess)
{
    this.IsBusy = true;
    Coroutine.Start(
        this.SaveStepsIterator,
        args =>
            {
                this.IsBusy = false;
                if (args.HasError)
                {
                    args.MarkErrorAsHandled();
                    this.DisplayErrorMessage("Error while saving record!", args.Error, true, false, true);
                    return;
                }

                // This need to be called if all operations completed successfuly
                if (this.ValidationErrors.Count == 0) onSuccess();
            });
}

private IEnumerable<INotifyCompleted> SaveStepsIterator()
{
    if (!this.OnBeforeIdeaBladeValidation()) yield break;

    this.CurrentItem.EntityAspect.ValidationErrors.Clear();
    this.CurrentItem.EntityAspect.VerifierEngine.Execute(this.CurrentItem);
    if (this.ValidationErrors.Count > 0) yield break;

    // Run Async validations
    this.TemporaryAsyncVerifiers = new List<Verifier>();
    var asyncValidationsOperation = Coroutine.StartParallel(this.AsyncValidationsBundle);
    yield return asyncValidationsOperation; // ------------------ SUSPEND WAIT FOR ASYNC VALIDATIONS TO COMPLETE

    // Add all verifiers popylated by async validations to engine, run verification and clean engine
    foreach (var verifier in this.TemporaryAsyncVerifiers) this.CurrentItem.EntityAspect.VerifierEngine.AddVerifier(verifier);
    this.CurrentItem.EntityAspect.VerifierEngine.Execute(this.CurrentItem);
    foreach (var verifier in this.TemporaryAsyncVerifiers) this.CurrentItem.EntityAspect.VerifierEngine.RemoveVerifier(verifier);

    if (this.ValidationErrors.Count > 0) yield break;

    // Save record
    yield return this.Repository.SubmitEntityManagerChanges(); // ---------------------- SUSPEND WAIT FOR SAVE TO COMPLETE
}

public override IEnumerable<INotifyCompleted> AsyncValidationsBundle()
{
    var userRepository = this.Repository as IUserRepository;

    // Validate user name to make sure no duplicates
    var checkUserNameOperation = userRepository.CheckForDuplicateUserName(this.CurrentItem.UserName, this.CurrentItem.UserKey);
    checkUserNameOperation.Completed += (sender, args) =>
        {
            if (args.Results.Any()) this.TemporaryAsyncVerifiers.Add(this.GetDummyVerifier("User with same user name already exist.", MEMUser.PropertyMetadata.UserName.Name));
        };
    yield return checkUserNameOperation;

    // Validate user email to make sure no duplicates
    var checkEmailAddressOperation = userRepository.CheckForDuplicateEmailAddress(this.CurrentItem.EmailAddress, this.CurrentItem.UserKey);
    checkEmailAddressOperation.Completed += (sender, args) =>
        {
            if (args.Results.Any())
            {
                var userName = args.Results.FirstOrDefault();
                if (!string.IsNullOrEmpty(userName))
                {
                    this.TemporaryAsyncVerifiers.Add(
                        this.GetDummyVerifier(
                        string.Format("User '{0}' has same email address. Email address must be unique", userName),
                        MEMUser.PropertyMetadata.EmailAddress.Name));
                }
            }
        };
    yield return checkEmailAddressOperation;
}