Generate node id when request come from MQTT broker

Setup, Configuration and Use Scripts & Rules
5

OK, this is doable but it is probably more appropriate for some other server outside of OH to do it for you (e.g. python script with a database). This is not the sort of problem that OH was designed to solve and keeping a running list of all currently assigned IDs will be challenging.

The ID needs to be unique, but are there any other requirements? For example, do they need to be sequential, a certain number of digits long, random, etc?

That will drive how this would work.

If I assume that the IDs need merely be sequential and you do not have to keep track of already assigned IDs you can do something like the following:

Prerequisites:

  • MQTT binding and MQTT Action installed
  • Persistence set up and CurrNodeID (see below) persisted with restoreOnStartup

Items:

String RequestID { mqtt="<[config]" } // config to subscribe to request for ID topic, message is the topic to publish the new ID to
Number CurrNodeID

Rules:

import java.util.concurrent.locks.ReentrantLock

val ReentrantLock idLock = new ReentrantLock()

rule "Next ID was requested"
when
    Item RequestID received command
then
    idLock.lock
    try {
        val nextId = (CurrNodeID.state as Number) + 1
        CurrNodeID.postUpdate(nextId)

        publish("brokername", receivedCommand, nextId.toString)
    }
    catch(Exception e){
        logError("ID", "Error calculating next Node ID: " + e.toString)
    }
    finally {
        idLock.unlock
    }
end

If you need more than sequential IDs and/or need to guarantee the nodes are unique, OH is not the best place to implement this.

Usual warning, I just typed in the above, there are likely errors.

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