How to set a field in JSON payload with value from context or environment?

General
1

I have a bunch of Change nodes that each set a JSON payload, representing requests to send to a device. One of the fields in each request is a password/PIN that the user needs to set. What is the best way for a user to input their PIN and get it into a field in these JSON payloads?

It seems like having them set their PIN as a global environment variable by going to Settings > Environment makes sense. But I can't figure out how to get that environment variable into the JSON payload in the Change nodes. I see that I can set the payload entirely with an environment variable but I can't figure out how set it as just a field in the JSON payload.

2

If you set a global environment var named password of type credential, then you would just in a change node
set msg. payload.property_name
to $ password
e.g.

[{"id":"412822c1a0915510","type":"inject","z":"d1395164b4eec73e","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{\"password\":\"\"}","payloadType":"json","x":860,"y":7840,"wires":[["0bcafb87d9cf2ec4"]]},{"id":"0bcafb87d9cf2ec4","type":"change","z":"d1395164b4eec73e","name":"","rules":[{"t":"set","p":"payload.password","pt":"msg","to":"password","tot":"env"}],"action":"","property":"","from":"","to":"","reg":false,"x":1120,"y":7840,"wires":[["c5875fdf482b668a"]]},{"id":"c5875fdf482b668a","type":"debug","z":"d1395164b4eec73e","name":"debug 2576","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":1350,"y":7840,"wires":[]}]

Where payload.property_name could be any property path.

p.s. When you say JSON, do you mean a JSON string or a javascript object? As you can only set the properties(fields as i think you have called them) of an object with a change node.

1 Like
3

If msg.payload is already a JSON object then you can use the change node to set an element of it

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If it isn't already JSON, you can make it so with two entries in the change node

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I assume that each user has their own installation of Node-red?
Because global environment variables are of course global and cannot be changed without a deploy.

I have a global environment variable set the way you propose.
Here is a snippet of my flows.json where it is defined

{
        "id": "a4687c609ba79692",
        "type": "global-config",
        "name": "global-config",
        "env": [
            {
                "name": "foo",
                "value": "bar",
                "type": "str"
            }
        ]
    },

This might not be appropriate for a PIN.

I think you can get things into flows_cred.json, which might be encrypted, sorry I can't recall how.

ps I don't know the difference between a JSON string and a javascript object (either?).
They sound like tomato and tomato to me :grinning:

4

Here are examples of each

[{"id":"fde2b3af12a6912e","type":"debug","z":"d1395164b4eec73e","name":"debug 2576","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":1030,"y":7580,"wires":[]},{"id":"47b271c80efe0eb8","type":"inject","z":"d1395164b4eec73e","name":"JSon (string)","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{\"test\":1}","payloadType":"str","x":830,"y":7540,"wires":[["d23062f8f87d1da0"]]},{"id":"d23062f8f87d1da0","type":"debug","z":"d1395164b4eec73e","name":"debug 2575","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":1050,"y":7540,"wires":[]},{"id":"e7d36681b8d82345","type":"inject","z":"d1395164b4eec73e","name":"javasript object","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{\"test\":1}","payloadType":"json","x":840,"y":7580,"wires":[["fde2b3af12a6912e"]]}]

And some light reading may offer some insight. JSON Vs. JavaScript: What is the Difference?

5

That's perfect. Yes, they're objects not strings. Thanks!

6

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