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

https://tracker.mender.io/browse/CFE-3733

On Monday, August 16, 2021 at 8:39:24 AM UTC-5 [email protected] 
wrote:

> 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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