CODEWITHSUNDEEP
ietf-netmod-yang
Sergio Sánchez
Sergio Sánchez

Reputation: 23

Yang Model recursive search for must condition

I have a problem with a restriction on my CLI. I've been investigating yang RFC7950 (https://www.rfc-editor.org/rfc/rfc7950) but I've found nothing.

Here is an example.

grouping httpGroup {
  list http-list{
    key "value";
    leaf value {
      status current { yexte:preliminary; }
      description "value to match";
      must "(not(../protocol)) and (not(../network-port)))" {
        error-message "Not compatible with protocol or non-TCP ports";
      }
      type string { length "1..255"; }
    }
  }
}

This group will be included in several groups with the following structure:

list and {
  leaf-list protocol { ..... }
  uses A;
  list or { 
    leaf-list protocol { ..... }
    uses A;
  }
}
grouping A {
  status{}
  leaf-list protocol { ..... }
  leaf-list X { ..... }
  uses httpGroup;
}

I need this must condition included in httpGroup to verify that protocol value has not been configured in any level of the hierarchy.

I've made this be adding more relatives paths to search for this node:

// same level
not(../protocol)

// next level
not(../and/protocol)
not(../or/protocol)

// previous level
not(../../protocol)
not(../../protocol)

//recursively down previous level
not(../../and/protocol)
not(../../or/protocol)

// third level
not(../and/or/protocol)
not(../and/and/protocol)

As you can see, this is not a clean solution at all.

Is there any way it can be done for a whole hierarchy like:

if protocol node exists and http-list exists then error.

Thank you in advance.

Upvotes: 2

Views: 1065

Answers (1)

predi
predi

Reputation: 5928

Groupings are meant to be reusable. It is a bad practice to attempt to create a grouping that may only be used in specific contexts. This is exactly what happens if you define an XPath expression within a grouping and this expression references nodes that are "outside" this grouping (a not yet known ancestor data node, for example, or even worse - an ancestor with a specific name).

The proper way for you to handle this situation would be to use a refine statement in each different context where this grouping is used. You target the value leaf with it, then refine it by adding a must statement, the expression of which of course depends on usage context. You do not define a must statement within grouping http-list.

Within grouping A:

grouping A {
  status{}
  leaf-list protocol { ..... }
  leaf-list X { ..... }
  uses httpGroup {refine "http-list/value" {must "not(../../protocol)";}}
}

As you can see, grouping A is now completely self-sufficient and may be used within any context - the must will not have any problems with it.

Upvotes: 1

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