Using data directly from the JSON output of MQTT

General
1

I have a working flow below, but I want to understand how to simplify it so my flows are cleaner (and learn something new). I was thinking a function node could do all of it, and would appreciate any pointers.

The input is a zigbee door sensor which output the JSON string over MQTT.
When the door is open (contact = false) I want the message to be passed onto a trigger node.
When the door is closed (contact = true) I want the message blocked.

Current flow and debugs:

01%20Zigbee2MQTT%20flow%20door%20sensor
01 Zigbee2MQTT flow door sensor.png1420Ă—378 42.1 KB

Change node:
02%20change%20node

Switch node:
03%20switch%20node

My basic thoughts of a function node would be:

var doorstate = msg.payload.contact;        //read contact state into a variable

if (doorstate = false)       // false means door is open
msg.payload = 1;            //any value works when sent to the trigger node

return msg;

I'm not sure how to read the payload from the MQTT node.
Also I 'think' a payload may still get passed through to the trigger node like this.

Thanks

3

You can set the mqtt node to ouput json directly, saves 1 node.

In the change node example, you change false to "false", could you explain why this is needed ?

The easiest would be to use a switch node and configure it like:

09
Screenshot 2019-10-22 at 18.26.09.jpg1024Ă—416 24.6 KB

1 Like
4

Hi @bakman2

It's because the switch node does not have a "== boolean true" option, so it did not work.
So I am changing it from a "booleon true" to a string which is "true".

Probably totally wrong logic on my part :slight_smile:

5

The is true and is false is the boolean test in the switch node.

1 Like
6

Of course! That makes sense thanks.
I believe I still currently need the change node to set the payload to "payload.contact".

Any tips how to read the JSON message from the MQTT node to get the contact state?

7

You don't need the change node - if the mqtt node outputs the example above.

mqtt (set the output to a parsed JSON object) -> switch node (configure it as shown in the reply above) -> trigger node

1 Like
8

Excellent - that all works with only the MQTT node > switch node > trigger node.

I really ought to look at all the node options in the future.

Thanks very much @bakman2 :+1:

1 Like