Tags and object IDs

[Nate Finch]

I always liked you, Tim :)

On Tue, Feb 2, 2016, 10:25 PM Tim Penhey <tim.penhey at canonical.com> wrote:

> Here is my short answer:
>
>   use names.UnitTag
>
> That is all.
>
> Tim
>
> On 23/01/16 09:53, Nate Finch wrote:
> > Working in the model layer on the server between the API and the DB.
> > Specifically in my instance, an API call comes in from a unit,
> > requesting the bytes for a resource.  We want to record that this unit
> > is now using the bytes from that specific revision of the resource.  I
> > have a pointer to a state.Unit, and a function that takes a Resource
> > metadata object and some reference to the unit, and does the actual
> > transaction to the DB to store the unit's ID and the resource
> information.
> >
> > On Fri, Jan 22, 2016 at 3:34 PM William Reade
> > <william.reade at canonical.com <mailto:william.reade at canonical.com>>
> wrote:
> >
> >     Need a bit more context here. What layer are you working in?
> >
> >     In general terms, entity references in the API *must* use tags;
> >     entity references that leak out to users *must not* use tags;
> >     otherwise it's a matter of judgment and convenience. In state code,
> >     it's annoying to use tags because we've already got the globalKey
> >     convention; in worker code it's often justifiable if not exactly
> >     awesome.
> >     See https://github.com/juju/juju/wiki/Managing-complexity#workers
> >
> >     Cheers
> >     William
> >
> >     On Fri, Jan 22, 2016 at 6:02 PM, Nate Finch
> >     <nate.finch at canonical.com <mailto:nate.finch at canonical.com>> wrote:
> >
> >         I have a function that is recording which unit is using a
> >         specific resource.  I wrote the function to take a UnitTag,
> >         because that's the closest thing we have to an ID type. However,
> >         I and others seem to remember hearing that Tags are really only
> >         supposed to be used for the API. That leaves me with a problem -
> >         what can I pass to this function to indicate which unit I'm
> >         talking about?  I'd be fine passing a pointer to the unit object
> >         itself, but we're trying to avoid direct dependencies on state.
> >         People have suggested just passing a string (presumably
> >         unit.Tag().String()), but then my API is too lenient - it
> >         appears to say "give me any string you want for an id", but what
> >         it really means is "give me a serialized UnitTag".
> >
> >         I think most places in the code just use a string for an ID, but
> >         this opens up the code to abuses and developer errors.
> >
> >         Can someone explain why tags should only be used in the API? It
> >         seems like the perfect type to pass around to indicate the ID of
> >         a specific object.
> >
> >         -Nate
> >
> >         --
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> >
> >
>
>
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