Filtering Messages

– in progress

In many integration workflows, not all messages need to be processed. Filtering out unwanted messages is a common practice to improve efficiency and ensure only relevant data moves through the system.

This involves checking key data elements in the message and deciding whether to process or discard it based criteria like message content or type.

Take the following interface workflow:

Use conditional logic to check messages against your filters

The Inbound HL7 message is parsed and passed to a filtering function along with the name of the message type.
if statements are used to call the filter.checkMsgType() function to test for messages to be filtered out.
The filtering rules are placed in a local filters.lua file so that we can separate concerns and create multiple rules to check.

local filter = require 'filters'
 
function main(Data)
   
   -- Parse the HL7 message
   local msg, name = hl7.parse{vmd = 'example/demo.vmd', data = Data}
   
   -- Filter out unwanted messages
   if not filter.filterMessage(msg, name) then  
      -- Map or Transform the message      
      -- Write the data to a destination
   end
   
end

How to structure filtering rules in filters.lua

The following sample filtering rules are intended to be a base for you to adapt to your own requirements.

-- This local module contains functions customized for this component only
 
local filter ={}
 
function filter.checkMsgType(Msg) 
   if Msg:nodeName() == 'Catchall' then
      iguana.logError('Unexpected message type.')
      return true
      
      -- use your own filter conditions and error messages
      elseif Msg.MSH[3][1]:nodeValue():lower() == 'interfaceware' then      
      iguana.logError('Rejecting test message from iNTERFACEWARE.')
      return true
      
      elseif Msg.PID[5][1][1][1]:nodeValue():lower() == 'addams' then      
      iguana.logError('No thing shall lurch or fester here!')
      return true
   end
   return false
end
 
return filter

The filter.filterMessage() function does the following:
- It filters out messages that match specified conditions
- It logs a meaningful error in each case
- It returns true (boolean) if a message should be filtered (false if it is ok to transmit)