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Publish to a Topic |
You want to publish a retained message to an MQTT topic on a broker.
Set the Retain option to true in the MQTT Output node configuration dialog, or set the retain message property to true in the message sent to the output node.
{% raw %}
[{"id":"4a7dc819.3aa6f8","type":"mqtt out","z":"eda2a949.74ea98","name":"","topic":"sensors/livingroom/temp","qos":"","retain":"true","broker":"61de5090.0f5d9","x":430,"y":420,"wires":[]},{"id":"fb7b873.c391878","type":"inject","z":"eda2a949.74ea98","name":"temperature","topic":"","payload":"22","payloadType":"num","repeat":"","crontab":"","once":false,"x":230,"y":420,"wires":[["4a7dc819.3aa6f8"]]},{"id":"61de5090.0f5d9","type":"mqtt-broker","z":"","broker":"localhost","port":"1883","clientid":"","usetls":false,"compatmode":true,"keepalive":"60","cleansession":true,"willTopic":"","willQos":"0","willPayload":"","birthTopic":"","birthQos":"0","birthPayload":""}]{: .flow} {% endraw %}
Once you have sent a retained message to a topic, all subscribers will receive that message when they subscribe. In Node-RED this occurs when an MQTT Input node is deployed. To clear a previously retained topic from the broker, send a blank message to that topic with the retain flag set.