How ConfD would evaluate an XPath expression with absolute path traversing a list?

YANG
1

Hi All,

Considering a yang module defined as follow:

module module1
{
	container a {
		list b {
			key name;
			
			leaf name {
				type string;
			}
			
			leaf x {
				type uint32;
			}
			
			leaf y {
				type uint32;
			}
			
			container c {
				when "(/a/b/x = 0) and  (/a/b/y = 1)";
				leaf cx {
					type uint32;
					mandatory true;
				}
			}
		}
	}
}

Everytime a new element is inserted into the list /a/b, I’ve noticed that ConfD always evaluates the condition statement “when” by iterating over all the entries of the list /a/b (sorted in crescent order) trying to match first /a/b/x = 0 and then /a/b/y = 1. The values x and y of the entry being inserted are ignored.

Can you please confirm if this is a correct behavior? If yes, can you kindly point me to the right XPath documentation explaining how to proceed when evaluating an absolute XPath value?

If relative paths (../x = 0) and (../y = 1), the evaluation is done using the values (x and y) of the new entry. This behavior sounds ok to me.

I would just like to confirm my understanding or have clarification about the meaning of the when condition in my example or how ConfD would evaluate it.

Thanks for your help.

2

When using an absolute path, you don’t want the when XPath expression to iterate over the entire list b, and only the current list entry x and y values. So you want to use current() (See RFC 7950). Example:

when "(/a/b[name=current()/../name]/x = 0) and  (/a/b[name=current()/../name]/y = 1)";
3

Ok, now it is clear. Thank you!