Help! JSONpath transformation drives me mad!

[jan_r]

Hi all,
as a openhab newbie I am stuck with the following: openhab is running on a raspberry. I want to integrate sensor data from an other raspberry by running a script via SSH which then returns a json output. My setup looks like this:

//default.things
Thing exec:command:temp_innen [command="ssh -i /scripts/id_rsa pi@raspi2 './temp.py'", interval=240, timeout=5, autorun=true]

//default.items
Number Temp_Innen "Temperatur [JSONPATH($.Temp):%.1f]°C" <temperature> (gEG,gMapDB) {channel="exec:command:temp_innen:output"} 
String Temp_Innen2 "Temperatur [JSONPATH($.Temp):%s]" <temperature> (gEG,gMapDB) {channel="exec:command:temp_innen:output"} 

//default.sitemap
Text item=Temp_Innen
Text item=Temp_Innen2

//karaf log
23:01:52.960 [DEBUG] [hab.binding.exec.handler.ExecHandler] - Exec [OUTPUT]: '{"Temp":   21.90,"Pressure": 1026.10}'
23:01:53.002 [DEBUG] [hab.binding.exec.handler.ExecHandler] - Transformed response is '{"Temp":   21.90,"Pressure": 1026.10}'

According to the log the script runs and returns json data. Using jsonquerytool.com it shows that the structure is correct. However only the String-Item Temp_Innen2 returns a value, e.g. 22.90. The Number item returns Temp_Innen NULL. Jsonpath doesn’t give me the value, only strings…

Can anybody give me a hint what’s wrong here? Or how to set-up the logging, that I get more debug info from the transformation? Help, please!

[Confectrician (Jerome Luckenbach)]

Could you try to use %s instead of %1.f in the number item?

You receive a json string from the exec action and JSONPATH probably expects the input to be a string.
Just an idea.
I can’t test this on mobile now, but it could be possible.

[Josar]

If you need the value as Number, I would suggest to make a setup like in this post:

Openhab2 RPI System Temperature and DS18B20 OneWire Chart with persistence

This tutorial is based on this, this, this and a lot of threads and tutorials i had to read till i got it working. I try to give a step by step Tutorial how to get a temperature chart with OpenHAB2 and the ExecBinding 2 using the RRD4J database for persistency. I will not explain everything in detail, please read this post to get an basic understanding of how OpenHAB works. And use the tutorials and the manual to get deeper insight of how the different parts work. Now to read out the CPU temp…

The exec thing returns a string, which cannot be directly stored in a number. So you can transform the string in a rule to a number and Update a number item with the converted value.

I also searched a solution for the same problem but did not find a better solution.

Items with channels REGEX and JSONPATH

@rlkoshak now i get that i can not add the channel of Exec to an Number item. I just tried to follow up your suggestion, which leaded me to this problem. So basically the Problem is the Exec Binding channel which returns a string and this can not be casted to a Number item. See the documentation. So that is obvious now. The return value of the exec binding channel will be stored in the item with applied Regex. In both cases it will be a string. Which can not be stored in the Number item. T…

I am not quite sure, but it seems that the transformation does not work as we both thing it is. But I had no time for an extensive research.

I hope that helps.

[jan_r]

Thanks for the help! It’s a bit odd that the transformation example in the user manual uses JSONPATH in a number item, but looking at your info it can’t be done this way. Is this a bug in the JSONPATH implementation in openhab?

Anyway - your tutorial makes sense as a alternative solution. That’s were I’ll proceed then…
Thanks again
Jan

[Josar]

I don´t know, maybe it worked like this in openHAB 1. I was not able to produce the shown examples in the manual.

But when i list the items in the karaf console i can clearly see that there is no assignment to cpuTemp.
cpuTemp_out is a string item added to the things output channel.
cpuTemp_rl is a number item updated by the type converted string in cpuTemp_out within the rule.
cpuTemp is an Number item linkt to the things output channel.

openhab> smarthome:items list
cpuTemp_out   (Type=StringItem, State=43470, Label=, Category=null)
cpuTemp_rl    (Type=NumberItem, State=43470.0, Label=, Category=null)
cpuTemp       (Type=NumberItem, State=NULL, Label=, Category=null)

As we can see there is nothing in the state of cpuTemp which could be then transformed with the rule of your jasonpath.