Extract values from a json object using a function node

[Luis GCU]

Hello gents 

I  am trying  to extract values from an json object using a function node, tried to many ways and nothing seems to work fro me.

the example below I would like to have function node with 5 outputs for the numeric values.

{ VFD_ID: 1, Humid: 34, Temp-f: 77, DewP-C: 8.04, HeatI-C: 25.51 }

this is the complete  message object 

raw: object

data: "{"VFD_ID":1, "Humid":34.00, "Temp-f": 77.00, "DewP-C":8.04, "HeatI-C":25.51 }"

ttl: "60"

published_at: "2017-04-27T01:58:12.046Z"

coreid: "2d0035001647343337363432"

evtname: "ENVIROMENT-DATA"

payload: object

VFD_ID: 1

Humid: 34

Temp-f: 77

DewP-C: 8.04

HeatI-C: 25.51

published_at: "2017-04-27T01:58:12.046Z"

id: "2d0035001647343337363432"

_msgid: "3b2d798c.c4d286"

thanks you

[Nate Damm]

I did something similar with a split and switch node for my bme280 sensor, but it spits out less info than this I believe.

first I used a split node with  ,

then a switch looking for each part, directed to individual outputs

Here's what debug shows me straight from that sensor,

"{"sensor":"bme280", "humidity":32.27, "pressure":939.14, "temperature":18.55, "altitude":634.05, "timestamp":1493262621}↵"

and heres how I did it,

[{"id":"78a17317.eda3ac","type":"split","z":"111d7925.30cd37","name":"","splt":",","x":230,"y":240,"wires":[["d64d3839.9c52d8"]]},{"id":"d64d3839.9c52d8","type":"switch","z":"111d7925.30cd37","name":"","property":"payload","propertyType":"msg","rules":[{"t":"cont","v":"\"humidity\":","vt":"str"},{"t":"cont","v":"\"pressure\":","vt":"str"},{"t":"cont","v":"\"altitude\":","vt":"str"},{"t":"cont","v":"\"temperature\":","vt":"str"}],"checkall":"true","outputs":4,"x":370,"y":200,"wires":[["c404b2e7.e4f15"],["fdf4dd2e.87b1"],["6b4f5b74.387c34"],["ca504f24.b00b2"]]}]

[steve rickus]

Hey Luis,

Let me see if I understand what you want -- the payload shown below should be split into individual msg objects? What do you want each msg to look like?

The node-red core 'split' node will break you payload into 5 msgs, each with a payload of the value, and a parts field with the key name and other internal information, like this:

4/26/2017, 11:23:10 PMnode: b9221c0b.21fe4msg : Object

object

_msgid: "d419232b.68c6f"

topic: ""

payload: 34

parts: object

id: "d419232b.68c6f"

type: "object"

key: "Humid"

index: 1

count: 5

The internal fields are used by the 'join' node to put them back together later (if you need to).

But, if you want to create individual msgs with a topic (the key) and a payload (the value), say for pushing to MQTT listeners, you can write a function node, something like this:

var keys = Object.keys(msg.payload);

var msgs = keys.map(function(key) {
    return { topic: key, payload: msg.payload[key] };
});
return [msgs];

If the number of output ports on your function node is 1, all 5 msgs will be sent down the same wire -- you can also set your output to 5 ports and have one msg sent to each port. Unfortunately, the order of the keys returned will not always be the same, so you can't count on a given topic always being sent to the same port number. So probably not a very robust solution, unless you write the code to build the output msgs array in a particular order.

Nate mentioned some of the struggles he had parsing his data string into keys and values. I can see that your payload is already an object, but in his case, I would pass the text to a 'json' node, which parses the text and builds the object for you -- much easier to manipulate in that form. And if you haven't seen it yet, I recommend you use the 'change' node with a JSONata expression if you need to restructure more complicated payload objects. Have fun!

--

Steve

[Glenn]

Does this page help

https://nodered.org/docs/writing-functions

eg msg1 = evtname.payload.VF_ID

[Luis GCU]

Hello guys

I have to try all your suggestion when I get to home today..

basically what I need is to display the value of each variable in dashboard , I did that using change node, I was trying to do the same using a function node instead of the change node ..

it luck ugly have change node  to extract the value of each variable .

See the capture attached.

regards, 

[steve rickus]

Instead of 5 change nodes, you could use "json" -> "split" -> "switch" (with 5 tests and 5 outputs - well maybe 6 to catch anything else)

The switch node can (for instance) test for msg.payload.parts.key == "Humid" and route the value to port #1, which is wired to the correct guage or chart.