How to filter Prepare Payments (AP503000) using status from an external async API without storing the status?

Hello 
 

I am customizing the Pay Bills screen and overriding the apdocumentlist delegate.

My requirement is:

• When a specific Payment Method is selected
• Only show AP Bills whose corresponding invoice in an external system has status Pending 
• The external invoice ID is already stored on APInvoice in a custom field such as UsrExternalInvoiceId
• I cannot store the external invoice status on APInvoice or in another database table

My current view override is similar to:
 

public delegate IEnumerable APDocumentListDelegate();

[PXOverride]
public IEnumerable apdocumentlist(APDocumentListDelegate baseMethod)
{
    IEnumerable baseResult = baseMethod();

    PayBillsFilter filter = Base.Filter.Current;

    if (filter == null ||
        !string.Equals(
            filter.PayTypeID,
            ExternalPaymentMethodID,
            StringComparison.OrdinalIgnoreCase))
    {
        return baseResult;
    }

    var filtered = new PXDelegateResult();

    foreach (object row in baseResult)
    {

        if (invoice == null)
            continue;

         APInvoiceExt ext =
            PXCache<APInvoice>.GetExtension<APInvoiceExt>(invoice);


        string externalInvoiceId =
            ext?.UsrExternalInvoiceId?.Trim();

        if (string.IsNullOrEmpty(externalInvoiceId))
            continue;

        // Need to retrieve the current invoice status from the external system here.

        // Only add the AP Bill if the external status is "Pending".
    }

    return filtered;
}

The external API method is asynchronous:

string response = await service.SearchInvoices(
    payerId,
    invoiceNumber: externalInvoiceId);

I do not want to use:

.GetAwaiter().GetResult()

or:

Task.Run(...)

to block the request.

Normally, for external API calls in Acumatica, I would use:

Base.LongOperationManager.StartAsyncOperation(
    cancellationToken =>
        SomeAsyncMethod(cancellationToken));

However, apdocumentlist is a synchronous IEnumerable delegate and needs the external API result immediately in order to decide whether each AP Bill should be returned.

Also, starting a long operation directly from a data view delegate does not appear to be the correct pattern as I understand.
 

Question

What is the recommended pattern approach for this scenario?

Specifically:

How should an asynchronous external API call be used when the result is required to filter a synchronous data view such as apdocumentlist?

 

The goal is simply:

APInvoice.UsrExternalInvoiceId
        ↓
Call External API
        ↓
Get current invoiceStatus
        ↓
If status == "Pending"
        ↓
Show bill on the grid

Could you please advise on the correct approach and share an example if possible? Please also correct me if my understanding is incorrect.