Assigning new value to MSH.10

I’m pulling a message out of the logs, and need to pass it back into another channel on the same server. The issue, however, is I need the MessageControlID to be changed. I’ve pulled the message into a translator, I’ve got this so far:

function modMessage(MsgIn)
   local T = hl7.parse{vmd='HL7_2.7.vmd',data=MsgIn}
   T.MSH[10] = T.MSH[10]..'_fromHold'
   MsgIn = tostring(T)
   return MsgIn
end

The error I’m getting is when I’m trying to reassign T.MSH[10], where I get:
Message Control ID is read-only, and cannot have a new value assigned to it.

After I reassign the value, I’ll put it back into a string and send it on its way, but I need to get past this hurdle. My searches in the KB were (as usual) not helpful.

-Robert James,
Interface Analyst,
GetWellNetwork, Inc.

You’ll need to make an HL7 tree you can alter. The trick is to do something like this:


function modMessage(MsgIn)
local Msg = hl7.parse{vmd='HL7_2.7.vmd',data=MsgIn}
local Out = hl7.message{vmd='HL7_2.7.vmd', name = Msg:nodeName()}
Out:mapTree(Msg)
Out.MSH[10] = Out.MSH[10]..'_fromHold'
MsgIn = tostring(Out)
return MsgIn
end


I may have the parameters the wrong way around but that is the general idea. The demo filter channel in Iguana shows this pattern.