Hello,
Is there a way to dynamically set a property in a change node?
Something like:
set flow.mode[msg.targetMode].enabled
to msg.payload
I know I can do it in javascript, but it would be better with a change node.
Thank you
Andy
This is possible with a jsonata expression ($eval) - here you can see an example:
Thanks for the quick answer.
I tried, but it not seams to work.
I try something like:
on the for or on the msg: $eval(topic) or $eval(msg.topic) to msg.payload
msg.topic containing "vip"
msg.payload containing "hello"
It results: flow.$eval(topic) = "hello"
Do you have a more basic exemple? When I read the thread, is looks more like a wish than a real feature.
Just show me what you tried (as exported flow). Also, which version of n-r do you have?
We are on 0.20.3
Here's the flow:
[{"id":"e9f00787.c7d228","type":"inject","z":"92c036c9.c74c08","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":480,"y":200,"wires":[["2d2b521.79b6fae"]]},{"id":"2d2b521.79b6fae","type":"change","z":"92c036c9.c74c08","name":"test","rules":[{"t":"set","p":"payload","pt":"msg","to":"hello","tot":"str"},{"t":"set","p":"topic","pt":"msg","to":"vip","tot":"str"},{"t":"set","p":"$eval(topic)","pt":"msg","to":"payload","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":650,"y":200,"wires":[["bc8ccf09.1f9f4"]]},{"id":"bc8ccf09.1f9f4","type":"debug","z":"92c036c9.c74c08","name":"dynamically set topic","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":910,"y":200,"wires":[]}]
Thank you
I wonder if eval is really needed? Is this what you want? Note that the key targetMode in the second rule is evaluated (not literal).
That won't do, because if the mode bbb already exists, with other properties, they get erased. The jsonata expression recreate the bbb property entirely instead of just targetting a sub-property.
Here's an exemple
[{"id":"e9f00787.c7d228","type":"inject","z":"92c036c9.c74c08","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":480,"y":200,"wires":[["2d2b521.79b6fae"]]},{"id":"2d2b521.79b6fae","type":"change","z":"92c036c9.c74c08","name":"test","rules":[{"t":"set","p":"payload","pt":"msg","to":"true","tot":"bool"},{"t":"set","p":"topic","pt":"msg","to":"vip","tot":"str"},{"t":"set","p":"mode.vip.name","pt":"msg","to":"vip","tot":"str"},{"t":"set","p":"mode","pt":"msg","to":"{topic: {\"enabled\": payload}}","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":650,"y":200,"wires":[["bc8ccf09.1f9f4"]]},{"id":"bc8ccf09.1f9f4","type":"debug","z":"92c036c9.c74c08","name":"dynamically set topic","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":910,"y":200,"wires":[]}]
Simplified dynamic property example:
[{"id":"b585fa52.babdb8","type":"inject","z":"c421dfeb.3e752","name":"","topic":"lala","payload":"{\"topic\": \"testtopic\"}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":402,"y":3350,"wires":[["aaf0b982.837278","8cc8db27.ee65e8"]]},{"id":"aaf0b982.837278","type":"change","z":"c421dfeb.3e752","name":"test","rules":[{"t":"set","p":"cfg.topicfield","pt":"msg","to":"topic","tot":"str"},{"t":"set","p":"topic","pt":"msg","to":"$eval(cfg.topicfield,payload)","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":611,"y":3355,"wires":[["8cc8db27.ee65e8"]]},{"id":"8cc8db27.ee65e8","type":"debug","z":"c421dfeb.3e752","name":"dynamically set topic","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":849,"y":3237,"wires":[]}]Indeed, fully agree.
I don't understand your flow sample. It seems it just take the property topicfield and us it as a value to overrite the topic with it. But the point would be to take the value of topicfield and use it as a dynamic reference to a propperty, so I could set the value with another property
topic = "lala"
msg.payload[topic].label = "the new value"
should result:
msg.payload.lala.label = "the new value"
All without recreating the lala object and preserving his properties.
Well, it looks like you dont want to "dynamically set a property" as you wrote in the title of your thread...
Seems like you want to create a property dynamically.
So you can support my feature request 
Meanwhile, this is only possible with a function node afaik.
Yes, I do want to do both! Create & set.
I'll support it.
I got it working with JSONata $merge function but I have not tested thoroughly to be confident that it works well.
[{"id":"475c2554.e9f5bc","type":"tab","label":"Flow 3","disabled":false,"info":""},{"id":"c79fba99.989f08","type":"inject","z":"475c2554.e9f5bc","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":160,"y":260,"wires":[["8539380c.7095e8"]]},{"id":"8539380c.7095e8","type":"change","z":"475c2554.e9f5bc","name":"test","rules":[{"t":"set","p":"payload","pt":"msg","to":"true","tot":"bool"},{"t":"set","p":"topic","pt":"msg","to":"lala","tot":"str"},{"t":"set","p":"mode.lala.name","pt":"msg","to":"vip","tot":"str"},{"t":"set","p":"final","pt":"msg","to":"{\"mode\" : {topic : $merge ([ $lookup(mode, topic) , {\"label\": \"new value\"}])}}","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":330,"y":260,"wires":[["5bbc8432.d8931c"]]},{"id":"5bbc8432.d8931c","type":"debug","z":"475c2554.e9f5bc","name":"dynamically set topic","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":590,"y":260,"wires":[]},{"id":"f81c9702.ccbf18","type":"inject","z":"475c2554.e9f5bc","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":160,"y":120,"wires":[["b52b8741.c6fa78"]]},{"id":"b52b8741.c6fa78","type":"change","z":"475c2554.e9f5bc","name":"test","rules":[{"t":"set","p":"payload","pt":"msg","to":"true","tot":"bool"},{"t":"set","p":"topic","pt":"msg","to":"lala","tot":"str"},{"t":"set","p":"mode.lala.name","pt":"msg","to":"vip","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":330,"y":120,"wires":[["8045059b.6421c8"]]},{"id":"8045059b.6421c8","type":"debug","z":"475c2554.e9f5bc","name":"dynamically set topic","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":590,"y":120,"wires":[]},{"id":"e728cba4.a57f08","type":"comment","z":"475c2554.e9f5bc","name":"Example","info":"","x":140,"y":80,"wires":[]},{"id":"340a83c9.74aa2c","type":"comment","z":"475c2554.e9f5bc","name":"Modified","info":"","x":140,"y":220,"wires":[]}]
