[aerogear-dev] New Android Pipeline

Kris Borchers kris at redhat.com
Wed Oct 3 11:35:40 EDT 2012 

On Oct 3, 2012, at 10:16 AM, Matthias Wessendorf <matzew at apache.org> wrote:

> Hello,
> 
>> But what do you do for entities that are properties of your child resources i.e. http://hostname/customers/100/orders?
>> 
>> I think it would be best to have another HttpRestAdapter with a new URL: http://hostname/customers/100/orders.
> 
> For this example (customers and orders of a specific customer), I
> _think_ you would model it with TWO pipes:
> 
> === HARD CODED EXAMPLE ===
> 
> // base pipeline
> Pipeline pipeline = new Pipeline("http://hostname/");
> 
> Pipe<Customer> customersPipe = pipeline.add("customers", Customer[].class);
> ==> maps to 'http://hostname/customers/'
> 
> Pipe<Order> ordersOfCustomer100 = pipeline.add("customers/100/orders",
> Order[].class);
> ==> maps to 'http://hostname/customers/100/orders'

This would not work because you would have a / in the name. You would want to set "customers/100/orders" as the endpoint and give the pipe some name like cust100Orders

> 
> So here, technically in the implementation detail you would actually
> have two _different_ HttpRestAdapter objects, one in the
> 'customersPipe' pipe and one in 'ordersOfCustomer100'.
> 
> Greetings,
> Matthias
> 
>> 
>>> 
>>>> 
>>>> It means, that if we want to get a single instance of a resource
>>>> (i.e. Task#100) we have to create a new HttpRestProvider with a
>>>> new URL.
>>>> 
>>>> For delete(), OTOH we can execute it with a specific id, and the
>>>> same goes for put() to perform an update of a child resource.
>>> 
>>> 
>>> Correct, a put on /tasks does make no sense. A delete on /tasks would
>>> (I guess in most cases) mean all items are deleted, which feels
>>> wrong....
>>> 
>> Sure, it's all relative to endpoint URL - to decide if it makes sense or not. But if I understand correctly the resource URL in our design should always be pointing to a resource type url (i.e. http://hostname/customers), and never to http://hostname/customers/100, or http://hostname/customers/100/orders), and that is the reason for current semantics of get(), delete(), post(), put() ?
>> 
>>> So IMO these put/delete operations make more sense on URIs, like
>>> /tasks/{id} (update / remove a single item).
>>> 
>>> 
>>> 
>>>> 
>>>> So we have GET, and POST operations performed on a 'parent'
>>>> resource, and DELETE, and PUT operations performed on child
>>>> resources. This asymmetry is confusing to me ... non-intuitive.
>>> 
>>> Hrm... I disagree, as indicated in my sentences on put/delete
>>> above...
>>> 
>>> I like Stefan's image on restful URIs:
>>> http://www.infoq.com/resource/articles/rest-introduction/en/resources/figure2.jpg
>>> 
>> 
>> +1
>> Actually I'd say this exactly describes the API and usage as I proposed it above :)
>> URL defines a resource, and GET, DELETE, POST, PUT operate on that exact resource URL.
>> In this scheme of things you never operate on a 'child' resource, as the 'child' resource is already expressed through a URL (i.e. http://hostname/customers/100, or http://hostname/customers/100/orders - a collection on a child resource).
>> 
>>> The above picture 'models' URIs for this UML diagram:
>>> http://www.infoq.com/resource/articles/rest-introduction/en/resources/figure1.jpg
>>> 
>> 
>> Actually I understand this as two layers where figure1 layer API, uses figure2 layer API.
>> That's the business interface layer that delegates to HttpRestAdapter, the two layer approach. In our case persistence view with operations like findById ...
>> 
>> 
>>> (Taken from this article =>
>>> http://www.infoq.com/articles/rest-introduction)
>>> 
>>> However the figure2.jpg shows as well, that there maybe cases where a
>>> DELETE on /tasks (or '/customers/{id}/orders') and a POST on
>>> /tasks/{id} (or '/orders/{id}') can make sense.
>>> 
>>> => We need to cover that too...
>>> If I recall correctly those two 'corner cases' are also not covered
>>> by
>>> the JavaScript library.
>>> 
>>> 
>>>> - I wouldn't eat exceptions, and return null even in a not-yet-real
>>>> exception handling :)
>>>> (https://github.com/danielpassos/aerogear-android/blob/new-pipeline/src/main/java/org/aerogear/android/core/HttpRestProvider.java#L86)
>>>> 
>>>> Really, either don't catch it, or if you do catch it, rethrow it as
>>>> is, or wrap into another - normally RuntimeException is perfectly
>>>> fine, so you don't pollute your API with throws declarations.
>>> 
>>> 
>>> +1 on this comment - but he added a TODO already ;)
>>> 
>> 
>> That's why I wrote 'even in a not-yet-real exception handling' i.e. don't _ever_ do it like that :)
>> 
>>> 
>>>> 
>>>> - I would use IllegalArgumentException here:
>>>> https://github.com/danielpassos/aerogear-android/blob/new-pipeline/src/main/java/org/aerogear/android/pipeline/AdapterFactory.java#L34
>>>> 
>>>> It's more appropriate, as it's a standard pattern for this kind of
>>>> use-case. By convention UnsupportedOperationException is used for
>>>> empty methods where interface contract is not fully supported.
>>>> 
>>> 
>>> +1
>>> 
>>> 
>>> 
>>>> - We have to do something about this "getId"
>>>> (https://github.com/danielpassos/aerogear-android/blob/new-pipeline/src/main/java/org/aerogear/android/pipeline/RestAdapter.java#L76)
>>>> 
>>>> One idea is to have an annotation - @Id. But scanning for
>>>> annotations needs to be done at init time or lazily on first use
>>>> ...
>>>> So maybe we could have an abstract base class with abstract method
>>>> getId() that every data object has to extend, and implement. A
>>>> simpler, and more robust solution actually, as compiler will
>>>> enforce it so there is no way for not providing one, as could
>>>> happen with forgotten or wrong placement of @Id annotation for
>>>> example.
>>>> 
>>> 
>>> I think the problem here is that not every object has an 'id', the
>>> field could be name 'recordId' - In JavaScript this is configurable.
>>> iOS has a TODO here...
>>> 
>> 
>> That's interesting. Can you give some examples?
>> 
>> 
>>> 
>>> -Matthias
>>> 
>>> 
>>> 
>>>> 
>>>> That's about it for now ... :)
>>>> 
>>>> - marko
>>>> 
>>>> 
>>>> ----- Original Message -----
>>>>> 
>>>>> 
>>>>> Hi guys
>>>>> 
>>>>> 
>>>>> I did some changes in the android library based on iOS stuff, it's
>>>>> closer to the pipeline adapter implementation. I would appreciate
>>>>> feedback and review.
>>>>> 
>>>>> 
>>>>> https://github.com/aerogear/aerogear-android/pull/1
>>>>> https://github.com/aerogear/aerogear-android-todo/pull/1
>>>>> 
>>>>> 
>>>>> Thanks,
>>>>> Passos
>>>>> _______________________________________________
>>>>> aerogear-dev mailing list
>>>>> aerogear-dev at lists.jboss.org
>>>>> https://lists.jboss.org/mailman/listinfo/aerogear-dev
>>>>> 
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>>> 
>>> 
>>> 
>>> --
>>> Matthias Wessendorf
>>> 
>>> blog: http://matthiaswessendorf.wordpress.com/
>>> sessions: http://www.slideshare.net/mwessendorf
>>> twitter: http://twitter.com/mwessendorf
>>> 
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> 
> 
> 
> -- 
> Matthias Wessendorf
> 
> blog: http://matthiaswessendorf.wordpress.com/
> sessions: http://www.slideshare.net/mwessendorf
> twitter: http://twitter.com/mwessendorf
> 
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