Hi Andrea & Justin
On Mon, Apr 14, 2014 at 5:05 PM, Andrea Aime
<andrea.a...@geo-solutions.it>wrote:
> On Mon, Apr 14, 2014 at 3:53 PM, Justin Deoliveira <
> jdeol...@boundlessgeo.com> wrote:
>
>> On Fri, Apr 11, 2014 at 5:54 AM, Sampo Savolainen <
>> sampo.savolai...@spatineo.com> wrote:
>>
>>> Hi justin,
>>>
>>> Maybe stored queries might be represented as a dimension for the layer.
>>> The default dimension would be to use no stored query, while stored queries
>>> returning values for that particular feature type would be values for that
>>> dimension. What do you think?
>>>
>>
> I thought we agreed that the stored queries params had a best fit with
> viewparams of a sql view. What changed?
>
Oh, nothing changed. This idea was not related to the parameter passed to
the stored query. The crazy thought that popped into my head was that we
could model FeatureTypes as having N dimensions where the first one is
accessible using filter encoding queries and the rest are accessible
through stored queries.
I was just thinking of ways on how to present the stored queries in the web
UI for the user and this option came to mind. I'm not sure it makes much
sense.
> And yes, I am checking that the the WFS supports stored queries before
>>> doing anything. Which actually brings up a small question regarding the WFS
>>> spec: when does a WFS service support executing stored queries? Does it
>>> have to support ListStoredQueries or DescribeStoredQueris or both
>>>
>>
>> As Ilkka mentions in his reply these are supposed to be part of the
>> lowest level of conformance (which surprised me) but I do still think it
>> would be a good idea to check the OperationsMetadata of the capabilities
>> document as the authoritative source. Which we will probably want to do
>> anyways in order to check whether we can create new stored queries, etc...
>>
>
> Hum... as far as I remember the server Sampo is trying to cascade only
> supports stored queries (and not regular GetFeature access)
> But is such a server even a valid WFS server?
>
You remember correctly. As Ilkka pointed out, the lowest level of
conformance requires stored queries but not filter encodings. It is a bit
wacky as opposed to how WFS has historically worked.
> Maybe this case should get special treatment top to bottom, like a special
> flag in the config telling the store to not even
> attempt to make a GetFeature, and GeoServer to disallow the publication of
> layers along the normal path, since
> if you don't configure the stored query params and their default values,
> you cannot even fetch data from it.
>
This is a good point. It would make sense for such stores to not advertise
the basic FeatureTypes. I'll look into that.
A quick progress update:
- wfs-ng can register 2.0 servers
- stored queries are listed as special feature types
- stored queries are handled by a specialized Content Feature Source
- StrictWFS_2_0_Strategy handles stored queries
- View params are passed into the strategy for handling
So basically the whole stack is working: I can make WMS queries to the
feature type created from the WFS-NG stored query data source.
The major hurdle now is mapping the relevant parts of the filter as stored
query parameters. I've hard coded a Filter envelope -> stored query
parameter conversion, but that's specific to the use case I'm working on
here. We need a more generic approach for this.
Is there a good, fast, expression language in use in GeoServer that I could
use for this? I'm thinking that we could us expressions to let users map
parts of the filter, feature type information, along with literals etc.
into the stored query parameters. This way we'll probably be able to make
this generic enough to be more universally useful. Plus the expression
language model should be extensible so we can cover future cases (new
requirements for the parameter mapping) by just adding more data to the
expression scope.
Sampo
--
Sampo Savolainen
R&D Director, Spatineo Oy
sampo.savolai...@spatineo.com
+358-407555649
Linnankoskenkatu 16 A 17, 00250 Helsinki, Finland
www.spatineo.com, twitter.com/#!/spatineo
www.linkedin.com/company/spatineo-inc
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