What is Comcom and Bus adapter?
Both Comcom and the bus adapter are automation servers developed by Microsoft for NAV. Comcom is a general communication component. All it does, is sending and receiving messages. You need to use a bus adapter with Comcom. The bus adapter is specific to the media used to transport the messages that Comcom sends and receive. At the moment there are two bus adapters: One for MS Message queue, and one for Named Pipes. In this document we will use the bus adapter for MS Message queue (MSMQ).
The reason for having Comcom as well as a bus adapter is, that you can create your application using Comcom without being concerned about what the transport media is going to be. When you decide on that / or if you want to change the media used, it will only require small changes – the application itself would need only very minor changes.
Prerequisites
Microsoft Dynamics NAV communication components come as part of SDK on the product CD. This needs to be installed before you start. And, you need to have MSMQ installed.
Create a new queue in MSMQ:
Open Computer Management, expand "Services and Applications", and you should see "Message Queuing" here, if MSMQ is installed. Expand "Message Queuing", and then expand "Private Queues". Note that the MSMQ Busadapter is only tested with private queues, and is unlikely to work with public queues.
Right click on "Private Queues", select New -> Private Queue, and enter a name. Let's call it MQueue. Also note that MSMQ Busadapter has not been tested for Transactional queues, so leave the field "Transactional" blank.
Now you have the queue, and the rest is up to Microsoft Dynamics NAV to send a message into this queue.
Create a new codeunit. First we need do declare the following variables to get access to Comcom:
Name Type Subtype
Comcom Automation 'Navision Communication Component version 2'.CommunicationComponent
ComOut Automation 'Navision Communication Component version 2'.OutMessage
OutStr Outstream
All automation variables need to be initialized before they can be used. Type these two lines to initialize Comcom and ComOut:
CREATE(Comcom);
ComOut := Comcom.CreateoutMessage('Message queue://');
'Message queue://' is the actual word Message queue. We need to tell Comcom to send the message in a format for Microsoft Message queue. But this is the only reference to the media (until we get to the bus adapter).
Remember, Comcom has only one purpose Sending/receiving messages. It is for writing the actual message that we want to send that we need OutStr. OutStr will contain the message, and Comcom will send it.
To associate Comcom with OutStr, add this line:
OutStr := ComOut.GetStream;
OutStr.WRITE('This is my message.');
Once the message is done, we just need to send it. Send it in this way:
ComOut.Send(0);
That’s the application done. Finally, we just need to add our bus adapter, which needs to be specific to what transport media we are using - in this case MSMQ.
Add one more global variable:
Name Type Subtype
MSBus Automation 'Navision MS-Message Queue Bus Adapter'.MSMQBusAdapter
To “plug in” the bus adapter, type in these lines at the beginning of the codeunit:
Create(MSBus);
MSBus.OpenWriteQueue('\Myqueue',0,0);
Comcom.AddBusAdapter(MSBus,0);
Your final codeunit should now look like this:
OnRun()
CREATE(Comcom);
CREATE(MSBus);
MSBus.OpenWriteQueue('Computername\Myqueue',0,0);
Comcom.AddBusAdapter(MSBus,0);
ComOut := Comcom.CreateoutMessage('Message queue://');
OutStr := ComOut.GetStream;
OutStr.WRITE('This is my message.');
ComOut.Send(0);
To test is, try to run it, then look the queue and see if the message was sent.
Next, we want to receive this message.
Receiving a message
Create a new codeunit with these variables:
Name Datatype SubType
Comcom Automation Navision Communication Component version 2'.CommunicationComponent
InMsg Automation Navision Communication Component version 2'.InMessage
InStr InStream
MSREBus Automation 'Navision MS-Message Queue Bus Adapter'.MSMQBusAdapter
Line Text 250
Highlight the Comcom variable, go to properties, and set the property WithEvents to Yes. This will create a new trigger called:
Comcom::MessageReceived(VAR InMessage : Automation "''.IDISPATCH")
This trigger will automatically run whenever there is a new message in the queue.
The finished codeunit should look like this:
OnRun()
CREATE(Comcom);
CREATE(MSReBus);
MSREBus.OpenReceiveQueue('computername\private$\lll',1,1);
Comcom.AddBusAdapter(MSREBus,1);
Comcom::MessageReceived(VAR InMessage : Automation "''.IDISPATCH")
InMsg := InMessage;
InStr := InMsg.GetStream;
InStr.READTEXT(Line);
MESSAGE(Line);
Go to Codeunit Properties, and set the property SingleInstance to Yes. Now, you can either run it from the object designer, or you set up NAS to run this codeunit.
First codeunit to send a message to MSMQ, and another codeunit which can listen to this queue, and which is triggered as soon as a message arrives.
