[katello-devel] ActiveResource as an alternative to custom RestClient-based Foreman api client

[Ivan Nečas]

That looks nice. As everything in Rails with basic CRUD. I've tried some 
real-world example though, here are my notes:

I tried to use ActiveResource to bind candlepin consumer model

I had to fix the monkey patch for replacing the (.json) suffixes first, then

consumer = Candlepin::Consumer.first
consumer.releaseVer # good, returns Candlepin::Consumer::ReleaseVer 
(note we haven't defined this class nowhere), I can access the 
releaseVer value, although it's not really Ruby convention to use 
camelCase for method names
consumer.releaseVer.releaseVer # => ""
consumer.releaseVer.releaseVer = "6Server"
consumer.save # 404, after some googling found out I have to use 
set_primary_key method (not documented btw. but we're used to it)
conusmer.save # second time, "getting NoMethodError: undefined method 
`strip' for nil:NilClass"
#fixed in newer version of ActiveResource, in 3.0.10 monkey patch needed

consumer.save # 500 from candlepin: 
"org.codehaus.jackson.map.exc.UnrecognizedPropertyException"
# why? because candlepin expects releaseVer to be a string (not a Hash)
# so I tried this
consumer.releaseVer="6Server"
consumer.save # => true
# we updated now

consumer.reload
consumer.name = "test2"
consumer.save # getting the same error with releaseVer issue
# nothing but a hack can fix this
# also if you wanted to see the request params in the logging, you would 
need to monkey patch
# while searching for a solution, I've also learned that support for 
singleton resources were introduced quite late [1]

Personally, it was very frustrating morning. And I don't want to go 
through this exercise on daily basis. I'm somehow still missing the pros 
of this solution. One of the criticism of the previous one was that we 
list the attributes in the client code. But it turns out it doesn't work 
without it in activeresource for us neither. But with the previous 
solution the list of params was at least in sync with the documentation.

I haven't found any resource that would say that ActiveResource deals 
with caching. Calling Candlepin::Consumer.find(uuid) twice in a row 
calls into Candlepin twice.

On the other hand, it seems that almost any customization in 
ActiveResource needs a monkey patch = really fragile.

And for the last year I can not think of any issue connected directly to 
the code in `lib/resources/` (a.k.a explicit bindings) that would not 
happened with ActiveResource. It would be really nice if writing unit 
tests was easier, but I don't see how ActiveResource would help us with 
this.

Another issue I  have with ActiveResource are all this implicit things 
that make the code harder to maintain and understand (explaining the 
meta-programming is always the hardest part in our Ruby course at Uni). 
Imaging you're a user of the client library and see something like this:

class Foreman::User < Resources::Foreman::Base
end

And let's assume you have no deep understanding of the Rails philosophy, 
let's say Katello or Foreman user (typical sysdamin) that wants to 
script something or fix a bug and send the patch back. It's not obvious 
that you can call.

users = Foreman::User.all
user = Foreman::User.find(id)
user.name = "New Name"
user.save
user.find(another_id)
user.destroy

So the next thing to do is to write documentation to the client library.

[1] - https://github.com/rails/activeresource/pull/4

-- Ivan

On 09/17/2012 08:04 PM, Dmitri Dolguikh wrote:
> Hey everybody,
>
> I finished the spike on using ActiveResource as a replacement for 
> RestClient, only for communication with Foreman, and only to 
> orchestrate user creation/deletion in Foreman. See the results at [1].
>
> Some post-spike thoughts/observations:
>  - I monkey-patched ActiveResource to support OAuth, but the same can 
> be achieved by subclassing ActiveResource::Base, which is the way to go.
>  - The amount of custom-code is *very* minimal and it's mostly to 
> support OAuth.
>  - Not a fan of custom to_json, we could either use resource's schema 
> (there are some drawbacks), or try using rabl [2] (like foreman folks do)
>  - Should we decide to adopt this, we can eventually move both 
> candlepin and pulp to use ActiveResource. I think it will be possible 
> to drop our lazy_attributes in the process with some work, if we adopt 
> rails caching.
>
>
> Comments, concerns?
> -d
>
>
> [1] https://github.com/witlessbird/katello/tree/foreman-ar-spike
> [2] https://github.com/nesquena/rabl
>
>
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-- 
Ivan




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