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

Documentation updated: 
https://docs.cfengine.com/docs/3.18/reference-functions-mergedata.html

On Monday, August 16, 2021 at 3:56:43 PM UTC-5 Nick Anderson wrote:

> 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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>> > > . 
>> > > 
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>>
>>

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