Re: mergedata, etc.: what happens with duplicate keys?

"'Vratislav Podzimek' via help-cfengine" <[email protected]> Mon, 16 Aug 2021 15:39:20 +0200
Newsgroups	gmane.comp.sysutils.cfengine.general
Message-ID	<[email protected]>
On Thu, 2021-08-05 at 03:19 -0700, [email protected] wrote:
> Thanks, Bas.  I'll take a look.
> 
> It seems that this behaviour ("last one wins") ought to be documented, so that we, the users, know
> what to expect, and that it is intentionally designed to behave this way.
> 
> Documenting it would also means that the behaviour should be preserved into the future.
> 
> Without such CFE documentation, it would be possible for a future implementation simply to change
> the behaviour. and for such a change to be called a "feature".  By adding documentation into CFE, it
> would means that any such change would be reasonably classified as a "bug" (or that such change
> would have earlier been planned, announced, managed, etc.).
> 
> I'd really like to see CFE themselves document and confirm this "last one wins" behaviour.
Could you please create a ticket at https://tracker.mender.io/secure/CreateIssue.jspa ?

Thanks!

--
Vratislav


> 
> -- David Lee
> On Monday, 2 August 2021 at 22:45:02 UTC+1 Bas van der Vlies wrote:
> > David,
> > 
> >  the cf_surfsara_lib also depends a lot of mergdate. The last one wins, see for a small example:
> >  * https://github.com/basvandervlies/cf_surfsara_lib#mustachejson-rules
> > 
> > 
> > regards
> > 
> > > On 31 Jul 2021, at 13:43, [email protected] <[email protected]> wrote:
> > > 
> > > All the documentation and examples about "mergedata" (and bundle "cmerge", etc.) seem to be
> > based on non-overlapping data sets. For example, with two simple key:value JSON datasets, the
> > examples and documentation have no overlap of keys.
> > > 
> > > But what is supposed to happen when the same key, and with potentially different value, appears
> > in both JSON datasets?
> > > 
> > > My proposed use-case is two simple JSON key:value datasets. The first can be regarded as a full
> > and complete set of default key:value pairs; the second is smaller and contains override values
> > for a subset of those same keys. The desired result would be that full set as modified by the
> > overrides.
> > > 
> > > There seems to be no documentation describing how this is handled, not even whether it is
> > regarded as an error condition. If it is documented somewhere, it seems well hidden.
> > > 
> > > If I should be using something else rather than "mergedata", let me know.
> > > 
> > > Any thoughts? Primarily about my proposed use-case, but also about improving the documentation
> > (e.g. at function "mergedata") to describe this case of same-key merging.
> > > 
> > > Assume CFE 3.12, but if CFE 3.15 would be different, that would be possible. (By the way my
> > reading of documentation also included some 3.18.)
> > > 
> > > -- David Lee
> > > 
> > > 
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