[openstack-dev] [mistral] Mistral Custom Actions API Design

lương hữu tuấn tuantuluong at gmail.com
Fri Mar 10 16:47:33 UTC 2017


I did not know about this change before but after reading the whole story,
IMHO i myself love the way of keeping it as simple at this moment as you
guys i think agreed on. For MixinAction or PolicyMixin, etc. we can develop
them later when we have concrete case studies.



On Fri, Mar 10, 2017 at 11:16 AM, Renat Akhmerov <renat.akhmerov at gmail.com>

> On 10 Mar 2017, at 15:09, Dougal Matthews <dougal at redhat.com> wrote:
> On 10 March 2017 at 04:22, Renat Akhmerov <renat.akhmerov at gmail.com>
> wrote:
>> Hi,
>> I probably like the base class approach better too.
>> However, I’m trying to understand if we need this variety of classes.
>>    - Do we need a separate class for asynchronous actions? IMO, since
>>    is_sync() is just an instance method that can potentially return both True
>>    and False based on the instance state shouldn’t be introduced by a special
>>    class. Otherwise it’s confusing that a classes declared as AsyncAction can
>>    actually be synchronous (if its is_sync() returns True). So maybe we should
>>    just leave this method in the base class.
>>    - I”m also wondering if we should just always pass “context” into
>>    run() method. Those action implementations that don’t need it could just
>>    ignore it. Not sure though.
>> This is a good point. I had originally thought it would be backwards
> incompatible to make this change - however, users will need to update their
> actions to inherit from mistral-lib so they will need to opt in. Then in
> mistral we can do something like...
> if isinstance(action, mistral_lib.Action):
>     action.run(ctx)
> else:
>     # deprecation warning about action now inheriting from mistral_lib and
> taking a context etc.
>     action.run()
> Yes, right.
> As far as mixin approach, I’d say I’d be ok with having mixing for
>> context-based actions. Although, like Dougal said, it may be a little
>> harder to read, this approach gives a huge flexibility for long term.
>> Imagine if we want to have a class of actions that some different kind of
>> information. Just making it up… For example, some of my actions need to be
>> aware of some policies (Congress-like) or information about metrics of the
>> current operating system (this is probably a bad example because it’s easy
>> to use standard Python modules but I’m just trying to illustrate the idea).
>> In this case we could have PolicyMixin and OperatingSystemMixin that would
>> set required info into the instance state or provide with handle interfaces
>> for more advanced uses.
> I like the idea of mixins if we can see a future with many small
> components that can be included in an action class. However, like you I
> didn't manage to think of any real examples.
> It should be possible to migrate to a mixin approach later if we have the
> need.
> Well, I didn’t manage to find real use cases probably because I don’t
> develop lots of actions :) Although the example with policies seems almost
> real to me. This is something that was raised several times during design
> sessions in the past. Anyway, I agree with you that seems like we can add
> mixins later if we want to. I don’t see any reasons now why not.
> Renat Akhmerov
> @Nokia
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