Restrict instance-identifier in must statement

YANG
1

I am trying to write must statement to restrict the instance-identifier, if ref is for instance of “/container/foo”, range should be from 1 to 100, if ref is for instance of “/ifs/if”, range should be from 101 to 200.
I am not sure how to write the must statement in container test below.

yang example:
container ifs {
list if {
key “name”;
leaf name {
type string;
}
}
}
container foo {
list bar {
key “name”;
leaf name {
type string;
}
}
}

container test {
/if ref is for instance of “/container/foo”, range should be from 1 to 100./
/if ref is for instance of “/ifs/if”, range should be from 101 to 200./
must “??” {}
error-message;
}
leaf ref {
type instance-identifier;
}
leaf range {
type uint32;
}
}

2

You can write your must statement as follows for the leaf node named range:

leaf range {
  type uint32;
  must "(starts-with (.., '/ifs:ifs') and . > 100 and . < 201)
         or (starts-with(.., '/ifs:foo') and . > 0 and . < 101)";
}

in which the first ifs after the / is the prefix for your YANG module.

1 Like
3

thanks, it works. thanks for helping on this, with tailf:annotate statement, there is a clear approach to have such validation logic yang model without polluting the original data model.
btw:do we have some typical use cases of using xpath for must statement? I don’t have much more knowledge on it.

4

The use of must statements in YANG models are very common. For example, it is being used in an IETF standardized YANG model called ietf-system.yang which is part of the linuxcfg example in the ConfD distribution.

5

Thanks for helping this :slight_smile:

6

if the case is instance-identifier to point to a deep path, which more list data node in that path (e.g. /foo/bar[name=n1]/bar2[name=n2]/bar3[name=n3]), I guess there is no way to use regex function from xpath 1.0 to match that path.
I know we have valdation callpoint can help on this, if it is can be done in yang model it could be better.

7

I found re-match function in manual, it could help this case.

8

Check out the extension tailf:path-filters in the tailf_yang_extensions(5) manual page.