I'm posting this as a potential solution. I imagine there are smarter ways of doing this. Hoping someone will jump in and show me the way 😁

I've written a classmethod that accepts 3 arguments: the lower and upper limits of the IDs to select, along with the number of records you'll want to select:

Class Sample.Rand
{
ClassMethod RandList(pMin As %Integer, pMax As %Integer, pLen As %Integer = 10) As %String [ SqlName = List, SqlProc ]
{
        Set tList = ""
        Set tCnt = 1
        For i=1:1:pMax
        {
            Set tNum = $R(pMax + 1)
            If tNum >= pMin
            {
                Set $LIST(tList,tCnt) = tNum
                Set tCnt = tCnt + 1
            }
            Quit:(tCnt > pLen)
        }
    Return tList
}
}

The method can be called as a custom SQL function in a subquery:

SELECT * FROM MyTable WHERE %Id %INLIST (SELECT Sample.List(MIN(%Id),MAX(%Id),10) FROM MyTable)

The query above will select up to 10 rows randomly from table MyTable.

Caveats: This could take a long time to run if your range from minimum to maximum %Id is large. And it's not guaranteed to return the number of rows specified as the 3rd argument (there may be deleted records, or insufficient random values generated before the upper limit for %Ids is reached). Finally, it assumes that %Id is numeric.

EDIT: And as pointed out by @Julius Kavay, @Robert Cemper has a better idea (he usually does 😉)

You should need only to iterate over the result set and populate the repetition of the PV1 field. Note that you reference PV1.7 (attending provider) in your narrative, but your code references PV1.3 (assigned patient location), so adjust the below as needed to identify the proper field:

//create a copy of the request
Set newREQ = pRequest.%ConstructClone()
//now we use the copy for manipulation
Set res=##class(%ResultSet).%New("%DynamicQueryGW:SQLGW")
Set sc=res.Prepare(sqlstring,,conn)
Set sc=res.Execute()
// create a repetition counter
Set cnt=1
While res.Next()
{
    Set RET = res.GetData(2)
    //Modify the segment
    //Reference the correct repetition for the current result set member
    set res = newREQ.SetValueAt(RET,"PV1:3("_cnt_")")
    //Increment the repetition counter
    Set cnt=cnt+1
}
Set sc=res.Close()
Set sc=conn.Disconnect()

The appropriate repetition delimiters as defined within the message schema (in this case "~") are automatically inserted.

Note that the SetValueAt() method has been modified with the assumption that you're using a consistent HL7 schema across all messages and know the correct path to the PV1 field in question. In that case the FindSegment() method should not be necessary.

ClassMethod TestObj() As %DynamicObject

{
        Set oM = {}
        Set mMode = ["down","up","click"]
        Set iter = mMode.%GetIterator()
        While iter.%GetNext(,.val)
        {
            Do oM.%Set(val,{"id":"","type":""})
        }
        Quit oM
}

USER> set oM = ##class(User.DynObj).TestObj()
USER> write oM.%ToJSON()
{"down":{"id":"","type":""},"up":{"id":"","type":""},"click":{"id":"","type":""}}
USER> zwrite oM.down.id
""
USER> zwrite oM.up.type
""
USER> set oM.click.type = "double"
USER> write oM.click.type
double
USER> write oM.%ToJSON()
{"down":{"id":"","type":""},"up":{"id":"","type":""},"click":{"id":"","type":"double"}}

To clarify, are you looking for a method to be used in a Business Process to obtain the path and name of a file created by a Business Operation?

I'm pretty sure you want the value to be 0 for the second option:

set ^%SYS("Portal","EnableAutoRefresh")=0

Messages for a Business Service would be queued in an external system if the service is unable to process them faster than they're being generated.

Are you referring to the time-in-queue for messages received by the service before they're acted upon by a Business Process or Operation?

If it's an ObjectScript process, you would use ..SendRequestSync() or ..SendRequestAsync(), with newrequest as the request argument and the name of the downstream process or operation as the target argument. Whether you would send it asynchronously or synchronously would depend on your needs. For healthcare integration, synchronous is generally required as it maintains FIFO.

You can't modify an inbound message from a service as it will have the immutable property set; that's why you have to clone it to make changes.

What class did you use for the inbound service?

I created a small batch of HL7 messages using nothing but newlines (newline is \n ... carriage return is actually \r). I consumed that file using a service based on EnsLib.HL7.Service.FileService and they were processed correctly.

If you used one of the HL7 service classes, what did you select for Framing?

Finally, is it possible that the messages you're testing with contain an actual backslash (\) character followed by the letter 'n' separating the segments? I've seen this happen before, believe it or not ...

I'm assuming you're working with Ensemble (or Interoperability as it's known in the most recent IRIS-based versions) ...

If you create a class that extends Ens.Rule.FunctionSet, not only will you be able to call its methods/functions from the DTL editor, they will appear as selectable functions in the drop-down list.