Re: [netmod] Backward Compatibility Question

On Mon, Oct 2, 2017 at 6:15 AM, JOEY BOYD <joey.boyd@adtran.com> wrote:

> Hello,
>
> Does anyone have thoughts on this?
>

The choice and case nodes are schema nodes so they are never an issue
for data tree XPath such as must/when.

The change works in your example because a leaf cannot be augmented.
If it was container and some other module augmented it, that module
will break if the container is changed to a choice.

>
> Regards,
> Joey
>

Andy

>
> -----Original Message-----
> From: JOEY BOYD
> Sent: Wednesday, September 27, 2017 9:06 AM
> To: 'netmod@ietf.org'
> Subject: Backward Compatibility Question
>
> Hi all,
>
> Suppose I had a published YANG model with the following leaf.
>
>
>   leaf thing1 {
>     type uint8;
>     description
>       "Thing 1.";
>   }
>
> Later, I realize that I wish I had modeled this in a choice as I now have
> a mutually exclusive option to 'thing1' which I want to add to the model.
>
>   leaf thing2 {
>     type empty;
>     description
>       "Thing 2.";
>   }
>
> This is a very simplified example but should be sufficient to demonstrate
> the problem.
>
> If I look at the XML representation of 'thing1', it looks like this.
>
> <thing1>123</thing1>
>
> If I were to move 'thing1' into a choice with a single case, it would look
> like this.
>
> choice things {
>   case thing1 {
>     leaf thing1 {
>       type uint8;
>       description
>         "Thing 1.";
>     }
>   }
> }
>
> Looking to the XML representation, it looks the same as before.
>
> <thing1>123</thing1>
>
> To me, this means that taking a single node or set of nodes and moving
> them under a case within a new choice statement is a backward compatible
> change. This assumes, of course, any mandatory or default behavior is
> preserved. I now can add 'thing2' to the existing model as an option to
> 'thing1'.
>
> choice things {
>   case thing1 {
>     leaf thing1 {
>       type uint8;
>       description
>         "Thing 1.";
>     }
>   }
>   case thing2 {
>     leaf thing2 {
>       type empty;
>       description
>         "Thing 2.";
>     }
>   }
> }
>
> Do you agree with this analysis or am I missing something?
>
> Best regards,
> Joey
>
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