>MO, if we are on the first page the Link-Previous header should be empty since there is no previous page. That will make it easier for people building the UI to know if they should show a previous link, etc. 
Ah yeah, I agree. I'll change that.

>Also, you can't have two parameters with the same name, should that actually be page=0&perPage=4?
Can't believe how I missed that. I'll fix that too.

Thanks!


On 11 January 2013 13:27, Kris Borchers <kris@redhat.com> wrote:

On Jan 11, 2013, at 5:01 AM, Daniel Bevenius <daniel.bevenius@gmail.com> wrote:

Hey Kris, 

been thinking about your reply regarding the inconsistency of the returned data. I think it looks a little odd to have the 'cars' property returned when requesting a single car.
What do you all think of this as a suggestion below?

I'm sorry, I misread that e-mail and thought these were both requests to the /cars endpoint and the data returned was formatted differently based on the data length. What you have makes sense so disregard what I said.


As you can see we now return HTTP Headers and also the object returned is either an array of cars, or just a single object if you only request a single car. 

Getting a page of Cars
URL="http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo"
curl -i --header "Accept: application/json" "$URL/cars?page=0&perPage=4"

The request will return:

HTTP/1.1 200 OK
Link-Previous: cars?page=0&page=4
IMO, if we are on the first page the Link-Previous header should be empty since there is no previous page. That will make it easier for people building the UI to know if they should show a previous link, etc. Also, you can't have two parameters with the same name, should that actually be page=0&perPage=4?
Link-First: cars?page=0&page=4
Same thing, page/perPage?

MetaData-PerPage: 4
MetaData-Page: 0
Link-Next: cars?page=1&page=4
Same as previous, if we are on the last page, there should not be a value for Link-Next. Also, as above, page/perPage?

Content-Type: application/json;charset=UTF-8
Content-Length: 161
[
  {"color":"Black","brand":"BMW","id":1},
  {"color":"Red","brand":"Ferrari","id":2},
  {"color":"Blue","brand":"Skoda","id":3},
  {"color":"Green","brand":"Audi","id":4}
]

Get a single Car

URL="http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo"
curl -i --header "Accept: application/json" "$URL/cars/1"

The request will return:

{"color":"Black","brand":"BMW","id":1}


On 10 January 2013 20:00, Daniel Bevenius <daniel.bevenius@gmail.com> wrote:
Summers brought up a good point today on IRC which I've forgot to mention. We've said that it will be possible to pass the page parameters as HTTP Headers and this is still the plan. But the demo is using the lastest from upstream and support for passing headers to the client is not there yet. I hope to have this working shortly though and I'll post back with information as soon as possible, tomorrow or Monday at the latest.




On 10 January 2013 15:32, Daniel Bevenius <daniel.bevenius@gmail.com> wrote:
>I know it's just a demo but I think making that JSON format consistent so that the car data is always in an array under the "cars" key would be better.
Good point. I'll change this so that there is always a "cars' key.


On 10 January 2013 15:13, Kris Borchers <kris@redhat.com> wrote:

On Jan 10, 2013, at 3:02 AM, Daniel Bevenius <daniel.bevenius@gmail.com> wrote:

We talked about paging yesterday on IRC, and it was decided to add a paging example to aerogear-controller-demo. What follows is an example to kick of further discussion about what the example should look like.

AeroGear Controller Demo Paging Route

This page discusses AEROGEAR-795 which is about adding an example to aerogear-controller-demo to demonstrate paging support so that the client libraries (Android, JavaScript, and iOS) can be tested against it.

This is only a suggestion and the implementation and the names of the query parameters can all be changed.

Use case

The example is using cars as the resource to interact with. To be able to query we need something to query, so lets start by adding some cars by posting.

Adding Cars

URL="http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo"

curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Black&car.brand=BMW" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Red&car.brand=Ferrari" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Blue&car.brand=Skoda" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Green&car.brand=Audi" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Yello&car.brand=Opel" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Pink&car.brand=Mini" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Gray&car.brand=Nissan" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Red&car.brand=Volvo" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Blue&car.brand=Saab" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Black&car.brand=Mazda" -X POST "$URL/cars"
curl -i --header "Accept: application/json" -H "Content-type: application/x-www-form-urlencoded" --data "car.color=Yello&car.brand=Golf" -X POST "$URL/cars"

The example uses an in-memory database so the data will be cleared upon redployment/restart of the server. So you only need to populate/post when you've restared or redployed.

With the cars in place, we can now issue GET requests with paging query parameters. The following route has been added to the demo:

route()
      .from("/cars")
      .on(RequestMethod.GET)
      .produces(MediaType.JSON.toString())
      .to(Cars.class).get(param("page", "0"), param("perPage", "-1"));

From this we can see that there are two optional parameters, page and perPage. If these are not specified all cars will be returned.

Getting a page of Cars

URL="http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo"
curl -i --header "Accept: application/json" "$URL/cars?page=0&perPage=4"

The request will return:

{
  "metadata":{"page":0,"perPage":4},
  "cars":[
            {"color":"Black","brand":"BMW","id":1},
            {"color":"Red","brand":"Ferrari","id":2},
            {"color":"Blue","brand":"Skoda","id":3},
            {"color":"Green","brand":"Audi","id":4}
          ],
  "links":{
          "first":"cars?page=0&page=4",
          "previous":"cars?page=0&page=4",
          "next":"cars?page=1&page=4"
          }
}

Getting the next page of Cars

To get the next page you can follow the next link:

URL="http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo"
curl -i --header "Accept: application/json" "$URL/cars?page=1&perPage=4"

{
    "metadata":{"page":1,"perPage":4},
    "cars":[
            {"color":"Yello","brand":"Opel","id":5},
            {"color":"Pink","brand":"Mini","id":6},
            {"color":"Gray","brand":"Nissan","id":7},
            {"color":"Red","brand":"Volvo","id":8}
           ],
    "links":{
            "first":"cars?page=0&page=4",
            "previous":"cars?page=0&page=4",
            "next":"cars?page=2&page=4"
            }
}

Get all Cars

URL="http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo"
curl -i --header "Accept: application/json" "$URL/cars"

Get a single Car

URL="http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo"
curl -i --header "Accept: application/json" "$URL/cars/1"

The request will return:

{"color":"Black","brand":"BMW","id":1}

Hmmm, the data returned should be consistent, right? Whether paging parameters are supplied or not, the structure of the JSON to access the car info should be the same. It's fine to leave out the metadata and links when they're not needed I guess but to access the car info, currently you have:

Not Paged: {"color":"Black","brand":"BMW","id":1}
Paged: {"cars":[{"color":"Black","brand":"BMW","id":1},…]}

I know it's just a demo but I think making that JSON format consistent so that the car data is always in an array under the "cars" key would be better.

Again, anything here can be changed, the name of the query parameters, the implementation, and what is returned.

Reference:

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