Alert rule on series of timestamps

Grafana Alerting
1

Trying to create an alert, when one of 5 temperature-sensors are not responding any more.
For this i use Infinity-Datasource and i grab the timestamps of the last update of all 5 objects in iobroker.

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Picture shows the result: One single value per sensor, so i have a series of 5 values.

Now i want to compare to actual time… the only way to get the time was to use a MySQL datasource and to ask for unix_timestamp.
grafik
Picture shows the result: One single value with actual time.

Now i create a math expresion to compare the 5 sensorvalues against actual time and define a threshold.

grafik
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This picture shows that all 5 values of the sensors show no alert, everything seems to be ok.

But when saving and waiting for some reaction, it turns into an error message:

grafik
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Where is my problem?
I assume it is the mismatch that i have 5 values in $D and only one in $A ???

Any way out of that?

2

Hi,

if you’re using Infinity Plugin datasource, is your data coming from an rest API? If it returns JSON and you could use Backend parser, you could get current time from JSONata (using $now()) and subtract the returned timestamps from $now. That way you would do everything in one datasource.

3

I was searching for a list of functions in jsonata yesterday but did not find any… so thanks for information.
But how to use it?

grafik
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If i put only “ts” in that Rows/Root window, then i see 5 ts-values below.
If i add the $now() i get a errormessage:

[sse.dataQueryError] failed to execute query [A]: error while performing the infinity query. error converting json data to frame: error evaluating JSONata expression left side of the “-” operator must evaluate to a number, position:7, arguments:

Am i doing something wrong ???

4

ah… got it… i do not need $now() i need $millis()…

5

Hmmm…
still issue with generating the correct output:

“$millis() - ts” works if the URL delivers one ts-value.
The result of the URL is with one value:
[{“id”:“mqtt.0.arduino.esp-c9cdb7.283C7734000000F4”,“val”:38.69,“ts”:1739451235918,“ack”:true}]

When selecting more values, for all 5 sensors, the result is:
[{“id”:“mqtt.0.arduino.esp-c9cdb7.283C7734000000F4”,“val”:39.06,“ts”:1739444929078,“ack”:true},{“id”:“mqtt.0.arduino.esp-c9cdb7.28A2EE370000009A”,“val”:33.44,“ts”:1739444929087,“ack”:true},{“id”:“mqtt.0.arduino.esp-c9cdb7.28FF64182188D2EF”,“val”:37,“ts”:1739444929129,“ack”:true},{“id”:“mqtt.0.arduino.esp-c9cdb7.28FF6418218C247D”,“val”:28.38,“ts”:1739444929129,“ack”:true},{“id”:“mqtt.0.arduino.esp-c9cdb7.28FF641821B04985”,“val”:36.12,“ts”:1739444929129,“ack”:true}]

and then the
“$millis() - ts”
does not work any more, it creates the errormessage
[sse.dataQueryError] failed to execute query [A]: error while performing the infinity query. error converting json data to frame: error evaluating JSONata expression right side of the “-” operator must evaluate to a number, position:0, arguments:

I have similar effect when using https://try.jsonata.org/… so i assume i need to modify syntax but can’t find the solution so far…