How to transform GET /messages from Thingy91

[Joakim U]

Hi,

Do you have a better example than the one on nRF Cloud that can show me how to transform a HTTP GET /message from my thingy. Right now, the messages are nested and it's quite difficult to just get a RSRP value for instance, as the response looks like this:

"items": [
        {
            "topic": "",
            "deviceId": "",
            "receivedAt": "2019-10-10T18:55:04.867Z",
            "message": {
                "data": "-42",
                "messageType": "DATA",
                "appId": "RSRP"
            },
            "tenantId": ""
        },
        {
            "topic": "",
            "deviceId": "",
            "receivedAt": "2019-10-10T18:55:04.560Z",
            "message": {
                "data": "101.5",
                "messageType": "DATA",
                "appId": "AIR_PRESS"
            },
            "tenantId": ""

How would the get request look like for this example?

I know it should start with the following, but after the exclusiveEnd part it becomes quite tricky. https://api.nrfcloud.com/v1/messages?inclusiveStart=2019-09-20T19%3A19%3A45.902Z&exclusiveEnd=2022-09-24T19%3A19%3A45.902Z 

[Markus Tacker (he/him)]

It's not possible to have the API transform the response in a way that it only returns the last "data" of the message that is a "RSRP" reading.

The closest you can get with a transform is this:

{
  "items": [
    "-42"
  ],
  "total": 1520,
  "nextStartKey": "..."
}

Use these parameters in addition to your date range:

• limit: 1
• transform: message.appId = 'RSRP' ? message.data : null

Example: 

https://api.nrfcloud.com/v1/messages?transform=message.appId%20%3D%20%27RSRP%27%20%3F%20message.data%20%3A%20null&inclusiveStart=2018-06-18T19%3A19%3A45.902Z&exclusiveEnd=2122-06-20T19%3A19%3A45.902Z&pageLimit=1

IMO the better approach is to process the answer in your client, since the transform will only be applied to the response, and not act as a query filter. You actually need to paginate all messages (at least for a specific device) until you find the latest RSRP message, since it might not be returned on the first page at all.

Then you can use e.g. in JavaScript: res.items.find(({message:{appId}}) => appId === 'RSRP').message.data to find the first RSRP message and extract the data.

[Joakim U]

Hi Markus,

Thank you for this solution, I can confirm that it works. I used the Javascript example that you suggested, which worked out great in the end.

Best regards

Joakim Uddenfeldt