Re: [yang-doctors] YANG must statement constraints

["Acee Lindem (acee)" <[e-mail]>]

Hi Lada, at 

One more thing to confirm (at least for now). A predicate for a list can reference non-key items in that list - right? For example:

       list foo {
              key "key";
              string key;
              string non-key;
       }

This is still valid - correct? 

    /some/xpath/foo[non-key="acee"]


Thanks,
Acee


On 3/19/21, 11:40 AM, "Ladislav Lhotka" <[e-mail]> wrote:

    On 19. 03. 21 16:17, Acee Lindem (acee) wrote:
    > Hi Lada, 
    > 
    > I guess the corollary would be that: 
    > 
    >    must "list/non-key-leaf != 42";
    > 
    > Is satisfied if there is at least one list entry with a non-key-leaf other than 42.

    Yes.

    > 
    > And,
    > 
    >      must not("list/non-key-leaf = 42)";
    > 
    > Requires all leaf entries to have non-key-leaf not equal to 42.

    Yes.

    > 
    > What if non-key-leaf is optional and not specified? Would this be equivalent to "!= 42" in the constraint evaluation?

    This is another tricky point of XPath. Either of the conditions "= 42"
    and "!= 42" is satisfied only if an instance exists and satisfies the
    condition. In other words, if no instance exists, then neither of the
    two conditions is true.

    Lada

    > 
    > Thanks much, 
    > Acee
    > 
    > On 3/19/21, 11:08 AM, "Ladislav Lhotka" <[e-mail]> wrote:
    > 
    >     Hi Acee,
    > 
    >     On 19. 03. 21 15:25, Acee Lindem (acee) wrote:
    >     > When the constraint references a non-key leaf in a list, do all members
    >     > of the list have to satisfy the constraint or only one of the list entries?
    > 
    >     It depends on how the constraint is written.
    > 
    >     If you have e.g.
    > 
    >         must "list/non-key-leaf = 42";
    > 
    >     then it is sufficient that at least one instance on non-key-leaf exist
    >     with that value. In contrast,
    > 
    >         must "not(list/non-key-leaf != 42)";
    > 
    >     requires all instances to have that value.
    > 
    >     Lada
    > 
    >     > 
    >     >  
    >     > 
    >     > Thanks,
    >     > Acee
    >     > 
    >     > 
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    > 
    >     -- 
    >     Ladislav Lhotka
    >     Head, CZ.NIC Labs
    >     PGP Key ID: 0xB8F92B08A9F76C67
    > 

    -- 
    Ladislav Lhotka
    Head, CZ.NIC Labs
    PGP Key ID: 0xB8F92B08A9F76C67