State / Command in MQTT messages


I’m currently using this line to switch on and off a heating panel:

Switch office_panel "Panel" <heating> (grpOffice) {mqtt=">[mosquitto:office/switch1/state:command:ON:1],>[mosquitto:office/switch1/state:command:OFF:0]"}

What’s not clear is what is the purpose of having both state and command on the same line? I’m assuming it is to set both topic (one with “ON” and the other with “1” and vice versa). This way I could “read” the state from another item, rule, script? Is MQTT persistence necessary? Is it better to have the controlled device (ESP module in this case) send the state and persist it when a command is issued (just in case it is set from somewhere else)?

Too many questions, sorry :confounded:

The “state” part of the binding above is actually part of the topic name. It could be anything. The “command” part of the above is to indicate that when this Item receives a command from OH to send a message to the topic. The “ON” and “OFF” part specifies which command received corresponds to which binding config. The “1” and “0” part indicates what the message to publish should be.

So the the binding means in English:

When the office_panel receives an ON command send the message “1” to the “office/switch1/state” topic on the mosquitto broker.

When the office_panel receives an OFF command send the message “0” to the “office/switch1/state” topic on the mosquitto broker.

This Item set up with outbound MQTT binding configs only. When office_panel receives a command the MQTT binding will send the appropriate message to the topic. You can read the state of office_panel from your rules but it doesn’t really necessarily reflect the state of the actual switch because you don’t have any incoming messages. If someone or something else switches the switch OH will not know about it.

Are you talking about mosquitto config or OH config. In OH, MQTT persistence is not necessary. In mosquitto it depends on whether you want to guarantee that OH receives all messages even if it happens to be down when the message is sent. Most likely the answer is no.

When possible it is best for the device to report its status if it can be controlled outside of OH. However, you will need to add an incoming binding config to your Item along the lines of:


This line means for any messages published to the topic “office/switch1/state” set the state of office_panel to the message.

The Switch Item is smart enough to convert “1” to ON and “0” to OFF for you so you do not need to specify a transform.


First of, thank you so much @rlkoshak for taking the time to reply and being so clear :slight_smile:

I added the line you suggested to the item:
Switch office_panel "Panel" <heating> (grpOffice) {mqtt=">[mosquitto:office/switch1/state:command:ON:1],>[mosquitto:office/switch1/state:command:OFF:0],<[mosquitto:office/switch1/state:state:default:.*]"}

I still can command it, but when I do, I get the following line in the log file:
[WARN ] [] - given new state is NULL, couldn't post update for 'office_panel'

Same happens if I publish either 0 or 1 to office/switch1/state from another MQTT client (some testing before I actually update the code in the ESP module). What could be wrong?

The MQTT binding may not be as smart as some of the others in converting 1 and 0 to ON and OFF. Instead of “default” you can use a MAPPING and create a mapping file to convert 1 to ON and 0 to OFF. or change your ESP module to send the strings “ON” and “OFF” which I can confirm does work (I use them in my setup).

This isn’t the syntax for the inbound binding config that you want to use. Instead of using the optional regex filter at the end, you want to replace default with a MAP transform:




So whenever a message arrives at the binding on the given topic, if it is a “1”, then it is replaced with “ON”, which the Switch item can parse (roughly speaking).

You may also want to add autoupdate="false" to the item binding, so the act of sending a command to the item does not immediately set the item’s state. With autoupdate="false", updating the state will only occur explicitly when a binding or rule updates the item’s state.

Last point: You may want to have two MQTT topics, one dedicated to commands to your device that your device subscribes to, for example office/switch1/command, and a separate topic that openHAB subscribes to, office/switch1/state, which reflects the state of the switch.

Complete item definition incorporating the above advice:

Switch office_panel "Panel" <heating> (grpOffice) {mqtt=">[mosquitto:office/switch1/command:command:ON:1],>[mosquitto:office/switch1/command:command:OFF:0],<[mosquitto:office/switch1/state:state:MAP(]", autoupdate="false"}

My setup:
EasyESP firmware on nodemcu.
Raspberry pi running openhab2 with mosquito mqtt broker.
In openhab2, i have install mqtt binding and MAP transformation.

home.items file for one of the switch.

Switch F2_Bedroom_Power “Power Outlet” (F2_Bedroom, gPower) {mqtt=">[broker:/nodemcu01/sw1/swcmd/cmd:command:ON:gpio,16,1], >[broker:/nodemcu01/sw1/swcmd/cmd:command:OFF:gpio,16,0], <[broker:/nodemcu01/sw1/swstat:state:MAP(]"} file content.

root@openHABianPi:/etc/openhab2/items# cat …/transform/

Using above i can able to command my switch ( on/off ) also,it updates the state of the switch if its turned ON/OFF externally.