How to convert a string to a number with Xpath

Setup, Configuration and Use Scripts & Rules
1

Hey Guys,

I created a counter with python for Raspberry Pi. The values will be saved in an XML file. With XPath I’m “extracting” the value in a string item. Now I’m struggling with converting the counter in a number item.

I’m using this rule therefore. It’s the rule from openhab doc.

rule "Convert XML to Item Type Number"
  when
    Item Temperature_xml changed
  then
    // use the transformation service to retrieve the value
    // Simple
    val mytest = transform("XPATH", "/*[name()='PTZStatus']
                                     /*[name()='AbsoluteHigh']
                                     /*[name()='azimuth']
                                     /text()", 
                                    Temperature_xml.state.toString )  
    // post the new value to the Number Item
    Temperature.postUpdate( newValue )
end

But I don’t know how to update the temperature item with postUpdate(newValue). It looks like it doesn’t work.
Someone an idea?

Thanks!

2

Why do you say this?

What do the logs say?

3

No error in the logs.
But number item is still empty and gives „NULL“ as feedback.

4

Add logs to see what the XPath is returning.

All transformations always return a string. However, if the XPath is returning a String that can be parsed into a number, you can update a Number Item with with it and it will work. If it’s not parsable, you’ll get an error in the logs.

Are you even certain this rule is running at all?

5

I’ve checked the logging and I got following error:

2022-12-20 22:18:31.534 [ERROR] [internal.handler.ScriptActionHandler] - Script execution of rule with UID 'gas-1' failed: The name 'newValue' cannot be resolved to an item or type; line 17, column 25, length 8 in gas
6

The rule only has two lines. You create mytest and then try to use newValue which doesn’t exist, as the error tells you.

7

Hey Guys,

I checked my logs and I found the following error:

2022-12-23 20:38:35.021 [ERROR] [internal.handler.ScriptActionHandler] - Script execution of rule with UID 'gas-1' failed: An error occurred during the script execution: Could not invoke method: org.openhab.core.model.script.actions.BusEvent.postUpdate(org.openhab.core.items.Item,java.lang.String) on instance: null in gas

Somebody an idea what it means?

Thanks!

8

Assuming the same rule as above, what ever mytest is, it’s not something that can be parsed into a number or a number with units.

It sure would be convenient if there were a way to see what mytest is.