context.AddErrorResult not updating UI

[waldenltd]

I have utilized the following code taken from another post:

using System;
using System.Threading.Tasks;
using Csla;
using Csla.Rules;

namespace WpfApp1
{
  [Serializable]
  public class PersonEdit : BusinessBase<PersonEdit>
  {
    public static readonly PropertyInfo<int> IdProperty = RegisterProperty<int>(nameof(Id));
    public int Id
    {
      get => GetProperty(IdProperty);
      set => SetProperty(IdProperty, value);
    }

    public static readonly PropertyInfo<string> NameProperty = RegisterProperty<string>(nameof(Name));
    public string Name
    {
      get => GetProperty(NameProperty);
      set => SetProperty(NameProperty, value);
    }

    protected override void AddBusinessRules()
    {
      base.AddBusinessRules();
      BusinessRules.AddRule(new PersonExistsRule(IdProperty));
    }

    [Create]
    [RunLocal]
    private void Create()
    { }
  }

  public class PersonExistsRule : BusinessRuleAsync
  {
    public PersonExistsRule(Csla.Core.IPropertyInfo IdProperty)
      : base(IdProperty)
    {
      InputProperties.Add(IdProperty);
    }

    protected override async Task ExecuteAsync(IRuleContext context)
    {
      int id = context.GetInputValue<int>(PrimaryProperty);
      var result = await DataPortal.FetchAsync<PersonExists>(id);
      if (result.Exists)
        context.AddErrorResult($"Item {id} already exists");
    }
  }

  [Serializable]
  public class PersonExists : ReadOnlyBase<PersonExists>
  {
    public static readonly PropertyInfo<bool> ExistsProperty = RegisterProperty<bool>(nameof(Exists));
    public bool Exists
    {
      get => GetProperty(ExistsProperty);
      private set => LoadProperty(ExistsProperty, value);
    }

    [Fetch]
    private async Task FetchAsync(int personId, [Inject] IPersonDal dal)
    {
      Exists = await dal.ExistsAsync(personId);
    }
  }
}

The issue is that when the code includes the database call and returns true context.AddErrorResult is called, but the UI is not updated. If I make the same call and comment out the database call context.AddErrorResult works as expected and the UI is updated. The application is a Blazer Web Assembly.

Any assistance would be greatly apprecate.

[rockfordlhotka]

In the page initialization do you set up a handler for the model changed event (from the viewmodel) so it calls StateHasChanged?

The rule is async, and when the result comes back from the app server something needs to tell Blazor to refresh data binding. Normally that's implemented by that event handler.