Tags and object IDs

[Tim Penhey]

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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