[aerogear-dev] New Android Pipeline

Marko Strukelj mstrukel at redhat.com
Wed Oct 3 12:23:28 EDT 2012 


----- Original Message -----
> On Wed, Oct 3, 2012 at 4:51 PM, Marko Strukelj <mstrukel at redhat.com>
> wrote:
> >
> >
> >> On Wed, Oct 3, 2012 at 3:00 PM, Marko Strukelj
> >> <mstrukel at redhat.com>
> >> wrote:
> >> >
> >> >
> >> >> Hello,
> >> >>
> >> >>
> >> >> On Wed, Oct 3, 2012 at 12:37 AM, Marko Strukelj
> >> >> <mstrukel at redhat.com>
> >> >> wrote:
> >> >> >
> >> >> > Some comments ... (I haven't looked at this that closely
> >> >> > before
> >> >> > so
> >> >> > there are some things here that relate to much earlier
> >> >> > commits).
> >> >> >
> >> >> >
> >> >> > - Logging seems to be the only android specific thing in the
> >> >> > library ATM. I'm thinking that maybe we could treat it as a
> >> >> > generic java client library using slf4j maybe, and provide
> >> >> > pluggability to wire it up to android.util.Log on Android.
> >> >> >
> >> >> > - I think Matthias noticed that the API is nicely aligned
> >> >> > with
> >> >> > the
> >> >> > one for iOS, which is exactly what we want. (I didn't
> >> >> > compare,
> >> >> > so
> >> >> > I can't say :)
> >> >> >
> >> >> > - Looking at HttpRestProvider get() method doesn't take an id
> >> >> > -
> >> >> > it's an operation that retrieves a list of all instances -
> >> >> > presuming URL points to something like http://host/task, and
> >> >> > not
> >> >> > to something like http://host/task/100.
> >> >> > (https://github.com/danielpassos/aerogear-android/blob/new-pipeline/src/main/java/org/aerogear/android/core/HttpRestProvider.java#L46)
> >> >> >
> >> >> > That makes sense in the HTTP meaning of GET.
> >> >>
> >> >>
> >> >> I'd use plural for endpoint URIs (e.g. /tasks and not /task)
> >> >>
> >> >> We need get() for retrieving _all_ items and get(id) for
> >> >> retrieving a
> >> >> single object (=> /tasks/{id}).
> >> >> (We also need 'queries', eventually)
> >> >>
> >> >> Regarding iOS... I left a TODO on the more high level 'filter'
> >> >> read
> >> >> (not implemented in the rest adapter)
> >> >> =>
> >> >> https://github.com/aerogear/aerogear-ios/blob/master/AeroGear-iOS/AeroGear-iOS/AGPipe.h#L55
> >> >>
> >> >> The 'filterObject' argument *could* be:
> >> >>  - an id to look up a single entity
> >> >>  - some more complex query object (e.g. a range or what not)
> >> >> ==> this all would translate in to a 'get()' invocation, where
> >> >> the
> >> >> method takes an argument.
> >> >>
> >> >> For looking up a single entity, of course I could have added a
> >> >> 'read(id)', which invokes an underlying 'http.get(id)'; Perhaps
> >> >> I
> >> >> add
> >> >> that read(id) now :)
> >> >>
> >> >> Anyways, back to Android... get() is fine for all, BUT get(id)
> >> >> is
> >> >> also needed.
> >> >
> >> > I think the question here becomes from what point of view should
> >> > we
> >> > understand terms get(), put(), post() ...
> >> > These are clearly meant as HTTP spec terms, so at least inside
> >> > this
> >> > class we should understand them strictly from that POV. So I
> >> > think
> >> > in terms of API a better approach would be to have a URL
> >> > represent
> >> > a full URL endpoint (asset type + a potential id for an
> >> > instance).
> >> >
> >> > That way GET, POST, PUT, DELETE retain their well defined
> >> > meaning.
> >> >
> >> > A wrapper API around this can then have a more business
> >> > interface
> >> > understanding of it (persistence understanding in our case -
> >> > with
> >> > operation names like: create, update, findById, query, delete).
> >> >
> >> > Or, we could add another series of methods called:
> >> >
> >> > getChild(String id), deleteChild(String id), postChild(String
> >> > id,
> >> > String content), putChild(String id, String content).
> >> >
> >> > 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.
> >> >
> >> >>
> >> >> >
> >> >> > 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).
> >>
> >>
> >> Not sure I follow your 'you never operate on a child resource' ...
> >> For
> >> me the 'http://hostname/customers/100' is a child resource (->
> >> member
> >> of the 'customers' collection)... So a PUT (for updates) against
> >> that
> >> 'http://hostname/customers/100' URI, is IMO doing the work on the
> >> child (member of the collection).... while, yes, the
> >> 'http://hostname/customers/100/orders' is a collection on a child
> >> resource (=> the 'orders collection' of the customer #100)
> >>
> >
> 
> 
> Hello,
> 
> > I mean in terms of HttpRestAdapter methods. One instance of
> > HttpRestAdapter represents one URL which (I assert) ATM always
> > maps to a resource-type URL - i.e. http://hostname/customers, not
> > http://hostname/customers/100.
> >
> 
> The Pipe (public) API maps to to the 'customers' pipe, for instance:
> 
> Pipeline pipeline = new Pipeline("http://hostname");
> Pipe<Customer> customersPipe = pipeline.add("customers",
> Customer[].class);
> 
> ATM, internally there is one 'http client' (e.g. HttpRestAdapter),
> that operates (currently) on the 'http://hostname/customers'
> endpoint.
> 
> So it supports something like this:
> 
> // read ONE customer:
> Customer c = customersPipe.read("100");
> 
> // give me ALL
> List<Customer> allCustomers = customersPipe.read();
> 
> which means, currently the ONE 'http client' object (read:
> HttpRestAdapter object) operates here on those 'two' URLs:
> - http://hostname/customers (base url)
> - http://hostname/customers/{id} (for a specific customer entity)
> 

Ok, I imagined it to work this way. And registering different types is required in order to have a working marshal/unmarshal - a layer wrapped around GET/POST/... layer handled by HttpRestAdapter.

So Pipes is already a more of a business type layer - specifically - a remote persistence layer for us.

> 
> 
> > So on HttpRestAdapter("http://hostname/customers") operations
> > operating on 'child' resources would be get(100), delete(100),
> > put(100, data). While operations operating on a resource itself
> > would be get(), and post().
> >
> > That's why I propose a slightly different operation naming scheme:
> > getChild(100), deleteChild(100), putChild(100, data). Even
> > postChild(101, data) if that made some sense - id field in data
> > would then have to be null for this to make sense. You still keep
> > get() for list of all children, delete() for removal of all
> > children (if we support a removal of a single child, then why not
> > removal of all children?), post(data) for adding new child when
> > and only when server is supposed to assign ID, while put(data)
> > makes no sense.
> 
> Ah, so, internally ... a mapping like this would occur:
> 
> 
> customersPipe.read("100") ==> restAdapter.getChild(givenId);
> customersPipe.read();   ==> restAdapter.get();
>

Yes.
 
> But, that still IMO would be done with the one object
> (this.httpProvider)...
>

Yes. So that makes Pipes API for java a wrapper around HttpRestAdapter.
Also from this a gather that Pipes API does not use GET/POST/PUT/DELETE naming scheme, but it is closely aligned with it nonetheless.
 
> 
> -Matthias
> 
> 
> >
> >
> >>
> >> >
> >> >> 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 ...
> >> >
> >>
> >> yes figure1 is the 'business' API, and figure2 shows how these
> >> 'methods' map to the URIs...
> >>
> >>
> >>
> >> >
> >> >> (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
> >> >> >>
> >> >> > _______________________________________________
> >> >> > aerogear-dev mailing list
> >> >> > aerogear-dev at lists.jboss.org
> >> >> > https://lists.jboss.org/mailman/listinfo/aerogear-dev
> >> >>
> >> >>
> >> >>
> >> >> --
> >> >> Matthias Wessendorf
> >> >>
> >> >> blog: http://matthiaswessendorf.wordpress.com/
> >> >> sessions: http://www.slideshare.net/mwessendorf
> >> >> twitter: http://twitter.com/mwessendorf
> >> >>
> >> >> _______________________________________________
> >> >> aerogear-dev mailing list
> >> >> aerogear-dev at lists.jboss.org
> >> >> https://lists.jboss.org/mailman/listinfo/aerogear-dev
> >> >>
> >> > _______________________________________________
> >> > aerogear-dev mailing list
> >> > aerogear-dev at lists.jboss.org
> >> > https://lists.jboss.org/mailman/listinfo/aerogear-dev
> >>
> >>
> >>
> >> --
> >> Matthias Wessendorf
> >>
> >> blog: http://matthiaswessendorf.wordpress.com/
> >> sessions: http://www.slideshare.net/mwessendorf
> >> twitter: http://twitter.com/mwessendorf
> >>
> >> _______________________________________________
> >> aerogear-dev mailing list
> >> aerogear-dev at lists.jboss.org
> >> https://lists.jboss.org/mailman/listinfo/aerogear-dev
> >>
> > _______________________________________________
> > aerogear-dev mailing list
> > aerogear-dev at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/aerogear-dev
> 
> 
> 
> --
> Matthias Wessendorf
> 
> blog: http://matthiaswessendorf.wordpress.com/
> sessions: http://www.slideshare.net/mwessendorf
> twitter: http://twitter.com/mwessendorf
> 
> _______________________________________________
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