[aerogear-dev] Server Side: Paging API with Metadata and Links (was: Re: Paging Demo)

[Douglas Campos]

On Sun, Jan 20, 2013 at 07:29:41AM -0800, danielbevenius wrote:
> I've been thinking about this and needed to make an update to the controller
> as I hade neglected to support returning query parameters in link headers,
> other than those used for paging. 
> 
> I've looked into Bruno's original suggestion and think it has a huge
> advantage in that the target endpoint class does not have to be changed, and
> can simply return a List<?>.
> 
> route()
>       .from("/cars")
>       .on(RequestMethod.GET)
>       .produces(MediaType.JSON)
>       .paged().offset())
>       .to(Cars.class).findCarsBy(param("offset", "0"), param("color"),
> param("limit", "10"));
> 
> For cases where the parameters 'offset' and 'limit' are named differently
> they could be configurable:
> route()
>       .from("/cars")
>       .on(RequestMethod.GET)
>       .produces(MediaType.JSON)
>       .paged().offset("myoffset").limitParamName("mylimit")
>       .to(Cars.class).findCarsBy(param("offset", "0"), param("color"),
> param("limit", "10"));
Well, I'm not a fan of putting the pagination info on the routes
themselves. Have you researched on using CDI interceptors for this? as
it's clearly an infrastructure concern.

So what about injecting pagination info via CDI? This means that we'll
need to use instance variables on the Controller class, and decorate it
during instantiation. The paging support could be enabled by using an
annotation on the controller method (@Paginated), and the CDI extension
would take care of wrapping the response/putting the headers
accordingly.

public class Cars {

	private PaginationInfo paginationInfo;

  @Paginated
	public List<Car> list() {
		// fetch offset/limit from this.paginationInfo
	}
}

The response would be decorated with the appropriate links.

Another option would be to have the method receiving the PaginationInfo
parameter, which would eliminate the need for annotations and stuff - if
you put the parameter on the signature, the response will be wrapped
automagically.

Thoughts?
 
> For now, I've just ignored support for a total as I think we need more time
> to investigate a proper solution for it, if we think it should be supported
> at all. The problem with having a callback is that in some situations, like
> the one above, that callback would also have to take a query parameter(s) so
> we'd need to do more work that like it initial idea were it would be
> possible to simply specify a name of a no-args method that returned an
> int/long.
We already got rid of total :)

-- qmx