On Tue, Nov 19, 2013 at 7:34 PM, Jeffrey Wood <[email protected]>wrote:
> Hi,
>
>
>
> I am working on a WFS request where we want results like an outer join,
> that is, we want to get all features from one table even if they do not
> have a match in the other.
>
Hi,
I concur with the solutions proposed by Tom, they both should help you get
what you want, or close to it, without having
to deal with the generality required for a core change (plus WPS supports
asynch requests, which is good if you plan to extract
large amounts of data, or if the joins end up being expensive).
Anyways, let's entertain the notion of doing it in the WFS protocol, as an
extension to the base protocol instead.
If we go beyond inner joins, we should consider setting up something that
leaves the door option to the other three join types, left, right, outer,
even if the initial implementation considers only outer.
The other issue to consider is that, in general terms, a query can contain
more than two feature types to be joined, or in other terms, more
than one join.
In SQL databases you specify the type of join, and then you don't need to
overload the meaning of and or or, because it's the type of
join that specified the desired behavior.
I'm wondering if something as follows could work, that is, adding a vendor
attribute specifying what kind of join should be considered:
<wfs:Query typeNames="layer1:ft1 layer2:ft2 layer3:ft3" aliases="ft1 ft2
ft3" jointype="inner outer">
And then the filters could be reorganized and split amount joining and non
joining:
* a filter is considered part of a join if it binds togheter more than one
feature type, and associated to the join that can see all the involved types
* anything involving a single feature type is non joining instead
And then the Join class and the machinery associated to in in the JDBC data
store should be updated accordingly.
Unfortunately I'm not very much up to speed with WFS 2.0 joining, so not
sure how much of the above is actually feasible:
we'd really need Justin to chime in, as he implemented the existing joining
code.
Cheers
Andrea
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