How to count relations?

[Alex Kavanagh]

On Wed, Jun 7, 2017 at 4:44 PM, Cory Johns <cory.johns at canonical.com> wrote:

> Alex beat me to it, but here's a marginally more complete example:
> https://gist.github.com/johnsca/a91cb5897d92dfb6741ee1a09d82b39b
>
> The key points are:
>
> * The interface needs to be UNIT scoped (because you care about individual
> units)
> * The joined handler sets a state for each unit that joins
> * The @when('rel.connected') predicate in the charm layer matches all
> units that have had that state set, so the set of conversations in the
> interface layer includes those units, and only those units.  This is
> trivially all of the units in my example, but you could also set a
> different state in a -changed handler based on data sent by each remote
> unit, and the conversations would only include the units that had that
> specific state set when you matched that state using @when
>
> Alex: A conversation will always have a scope, so that list comprehension
> isn't necessary.
>

Ah, interesting Cory.  It must have been a bug then; I ran into a situation
where scope was None and had to filter it out; maybe I can remove that
check from the interface I wrote (manila-plugin).

Thanks!
Alex.


> On Wed, Jun 7, 2017 at 11:38 AM, Alex Kavanagh <
> alex.kavanagh at canonical.com> wrote:
>
>> Hi
>>
>> I'm assuming you are using charms.reactive; if not then look into
>> relation_ids command.
>>
>> In your interface, count the number of conversations that have a scope
>> set to something other than None.  scope shouldn't be None, but I've had
>> cases where it has been (it may have been a bug):
>>
>> So in the provider.py RelationBase derived class, something along the
>> lines of:
>>
>> num = len([c for c in self.conversations() if c.scope])
>>
>> in a method would be a relatively simple way of doing it.
>>
>> (There may be better ways of doing this!)
>>
>> Cheers
>> Alex.
>>
>> On Wed, Jun 7, 2017 at 4:22 PM, fengxia <fxia1 at lenovo.com> wrote:
>>
>>> Hi Juju,
>>>
>>> I'm building two charms and linking them with one relation, one charm
>>> ("A") will provide and the other ("B") will require.
>>>
>>> The deployment will have one "A" and three "B"s. How do I know all three
>>> Bs have joined? I'm thinking to use a counter in A's relation, then at
>>> relation-joined hook by B to add this counter. But set_remote() and
>>> set_local() didn't work. Not sure what's the right way to achieve this?
>>>
>>>
>>> --
>>> Feng xia
>>> Engineer
>>> Lenovo USA
>>>
>>> Phone: 5088011794
>>> fxia1 at lenovo.com
>>>
>>> Lenovo.com
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>>>
>>>
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>>
>>
>>
>> --
>> Alex Kavanagh - Software Engineer
>> Cloud Dev Ops - Solutions & Product Engineering - Canonical Ltd
>>
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>


-- 
Alex Kavanagh - Software Engineer
Cloud Dev Ops - Solutions & Product Engineering - Canonical Ltd
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