Docs on Ens.BusinessOperation class, QueueCountAlert property state:

Number of messages on this item's queue needed to trigger an Alert message to be sent. Note that no further alerts will be sent unless the number of messages on the queue drops below 80% of this number and then rises again to this number. Note that this alert will be sent even if AlertOnError is False. Zero means no alerts of this type will be sent.

This line causes an error:

Write tMessage.Name,!

Your class does not have Name property, so it causes an error.

The following method works :

/// Do ##class(Testing.Messages.Session).test()
ClassMethod test()
{
    Set messagedata = "<?xml version=""1.0"" encoding=""UTF-8""?><session><sessionId>124364</sessionId><cabinet>demo</cabinet><eventType>IN</eventType><eventTime>20161006160154</eventTime><login>test</login><loginFirstName>test</loginFirstName><loginLastName>test</loginLastName></session>"
    Set reader = ##class(%XML.Reader).%New()
    Set status = reader.OpenString(messagedata)
    Do reader.Rewind()

    If $$$ISERR(status) {do $System.Status.DisplayError(status)}

    // Associate a class name with the XML element name
    Do reader.CorrelateRoot("Testing.Messages.Session")

    // Read objects from xml data
    While (reader.Next(.tMessage,.status)) {
        Do:$$$ISERR(status) $System.Status.DisplayError(status)
        Write tMessage.sessionId,!
    }
}

Terminal:

USER >do ##class(Testing.Messages.Session).test()
124364

Disclaimer. I am not familiar with EDI.

Some solutions would be:

  • Get official EDI 271 xsd schema files and import them into Caché
  • Alternatively you can read EDI 271 specification/check examples and write your own classes

Then you need a dtl to transform incoming message into your new classes. If there's a lot of them maybe it would be better to write one generic transformer or write a transformer generator based on class (which would generate transformation method based on class properties).

After that you  can transform your class object into json via several ways:

  • Old json via %ZEN.proxyObject/%ZEN.auxillary.jsonProvider
  • New json via dynamic objects