# Search for data in msg. payload based on values within payload. Is this possible?

**URL:** <https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882>\
**Category:** General\
**Created:** [27 October 2020 10:28 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882 "2020-10-27T10:28:32Z")\
**Posts on this page:** 11\
**Page:** 1

<div class="post-metadata">

**Author:** ![NoMercyMike](https://avatars.discourse-cdn.com/v4/letter/n/3be4f8/32.png) [@NoMercyMike](https://discourse.nodered.org/u/NoMercyMike)\
**Post date:** [27 October 2020 10:28 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/1 "2020-10-27T10:28:32Z")

</div>

Hi,

I'm using node red for a while now as rule engine for my home automation system. Now I've stumbled over a problem, I cannot solve by myself. Every idea how to solve is highly welcome 🙂

The problem is hard to explain, because I'm not a native English speaker, but I try to...

I try to get information about my heating system with a Rest-API call and want to use the received information (as object) in a flow. This works so far but...

When requesting e.g. "outside temperature" from my heating system the received msg-object looks like this (shortened):

```auto
{
    "_msgid": "b4d8608.3e462a",
    "payload": {
        "properties": {
            "value": {
                "value": 8.2,
                "type": "number"
            },
            "status": {
                "value": "connected",
                "type": "string"
            },
            "unit": {
                "value": "celsius",
                "type": "string"
            }
        },
        "path": "properties.value.value"
    },
    "statusCode": 200
}

```

So the value of _msg.payload.path_ tells me where to find the value I want to extract. In this example it is at _msg.payload.properties.vale.value_

Another example when asking the REST-API e.g. for the "outside temperature" is:

```auto
{
    "_msgid": "5f35fd23.ced484",
    "payload": {
        "properties": {
            "active": {
                "value": true,
                "type": "boolean"
            },
            "demand": {
                "value": "unknown",
                "type": "string"
            },
            "temperature": {
                "value": 22,
                "type": "number"
            }
        },
        "path": "properties.temperature.value"
    },
    "statusCode": 200
}

```

Here the value of _msg.payload.path_ tells me that the value I want to extract is at _msg.payload.properties.temperature.value_

Is it possible, maybe with a change node and JSONata, to first get the value of msg.path and use this value as path to the value I want to extract??? How???

I played a bit with JSONata but with our success ☹

Regards,  
Michael

---

<div class="post-metadata">

**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [27 October 2020 11:18 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/2 "2020-10-27T11:18:48Z")

</div>

Welcome to the forum @NoMercyMike.

In a function node this is one way to do it

```auto
let value = eval(`msg.payload.${msg.payload.path}`)

```

but I don't like using eval. I suspect there is a better way using something like  
`msg.payload[msg.payload.path]`  
but that doesn't work.

---

<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [27 October 2020 12:17 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/3 "2020-10-27T12:17:52Z")

</div>

Yes the same way as in function node with $eval  
e.g.

```auto
[{"id":"932dafe1.4093b8","type":"inject","z":"8d22ae29.7df6d","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{\"properties\":{\"value\":{\"value\":8.2,\"type\":\"number\"},\"status\":{\"value\":\"connected\",\"type\":\"string\"},\"unit\":{\"value\":\"celsius\",\"type\":\"string\"}},\"path\":\"properties.value.value\"}","payloadType":"json","x":120,"y":2500,"wires":[["e8ea619b.7e60a","f98b95cf.92cb"]]},{"id":"e8ea619b.7e60a","type":"change","z":"8d22ae29.7df6d","name":"","rules":[{"t":"set","p":"payload","pt":"msg","to":"$eval(\"payload.\" & payload.path)","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":330,"y":2500,"wires":[["f98b95cf.92cb"]]},{"id":"f98b95cf.92cb","type":"debug","z":"8d22ae29.7df6d","name":"Na Template","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":620,"y":2300,"wires":[]}]

```

---

<div class="post-metadata">

**Author:** ![shrickus](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/shrickus/32/517_2.png) [@shrickus](https://discourse.nodered.org/u/shrickus)\
**Post date:** [27 October 2020 12:30 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/4 "2020-10-27T12:30:24Z")

</div>

The way I would do it is to use the JSONata `$eval(...)` function inside a `change` node, with this expression:

`payload.$eval(path)`

I tried the `$lookup(...)` function, but that only appears to search 1 level, not the 3 listed in the 'path' string...

---

<div class="post-metadata">

**Author:** ![hotNipi](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/hotnipi/32/383_2.png) [@hotNipi](https://discourse.nodered.org/u/hotNipi)\
**Post date:** [27 October 2020 13:27 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/5 "2020-10-27T13:27:08Z")

</div>

Without eval

```auto
var path = msg.payload.path.split(".")
while(path.length){
    msg.payload = msg.payload[path.shift()]
}
return msg;

```

---

<div class="post-metadata">

**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [27 October 2020 13:56 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/6 "2020-10-27T13:56:25Z")

</div>

I like that way. Eval is dangerous as if you get something unexpected, or even malicious, in path it will execute it.

---

<div class="post-metadata">

**Author:** ![hotNipi](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/hotnipi/32/383_2.png) [@hotNipi](https://discourse.nodered.org/u/hotNipi)\
**Post date:** [27 October 2020 13:58 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/7 "2020-10-27T13:58:30Z")

</div>

It is just a quick and dirty example. If path is incorrect it fails pretty hard. So needs improvements for real usage.

---

<div class="post-metadata">

**Author:** ![Steve-Mcl](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/steve-mcl/32/4826_2.png) [@Steve-Mcl](https://discourse.nodered.org/u/Steve-Mcl)\
**Post date:** [27 October 2020 19:04 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/8 "2020-10-27T19:04:39Z")

</div>

You can use the builtin helper function `RED.util.getMessageProperty` ...

> `getMessageProperty(msg,expr)`  
> `msg` is the object to "get" a value from  
> `expr` is the path to the item

so instead of passing `msg` in, pass `msg.payload` in.

FUNCTION CODE...

```auto
msg.value = RED.util.getMessageProperty(msg.payload, msg.payload.path);
return msg;

```

Demo...

```auto
[{"id":"2a6df415.f905fc","type":"inject","z":"1ce23005.82287","name":"fake it","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{ \"properties\": { \"active\": { \"value\": true, \"type\": \"boolean\" }, \"demand\": { \"value\": \"unknown\", \"type\": \"string\" }, \"temperature\": { \"value\": 22, \"type\": \"number\" } }, \"path\": \"properties.temperature.value\" }","payloadType":"json","x":380,"y":780,"wires":[["158d361d.bd639a"]]},{"id":"158d361d.bd639a","type":"function","z":"1ce23005.82287","name":"","func":"debugger\nmsg.value = RED.util.getMessageProperty(msg.payload, msg.payload.path);\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","x":530,"y":780,"wires":[["e5e22824.4b89c8"]]},{"id":"e5e22824.4b89c8","type":"debug","z":"1ce23005.82287","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":690,"y":780,"wires":[]}]

```

---

<div class="post-metadata">

**Author:** ![NoMercyMike](https://avatars.discourse-cdn.com/v4/letter/n/3be4f8/32.png) [@NoMercyMike](https://discourse.nodered.org/u/NoMercyMike)\
**Post date:** [27 October 2020 19:12 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/9 "2020-10-27T19:12:36Z")

</div>

Many thanks @all 🙂

At least the solution from Steve-Mci worked for me. Great!!!

---

<div class="post-metadata">

**Author:** ![shrickus](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/shrickus/32/517_2.png) [@shrickus](https://discourse.nodered.org/u/shrickus)\
**Post date:** [28 October 2020 15:08 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/10 "2020-10-28T15:08:33Z")

</div>

True, I always try to avoid using eval in Javascript... but I'm less worried about it inside a JSONata expression, where the data is all sand-boxed and there is no access to the file system.

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [11 November 2020 15:08 UTC](https://discourse.nodered.org/t/search-for-data-in-msg-payload-based-on-values-within-payload-is-this-possible/34882/11 "2020-11-11T15:08:36Z")

</div>

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