Hi Steve,
Have a look at this table:
http://www.hibernatespatial.org/documentation/03-dialects/01-overview/
It provides an overview of the HQL functions that are supported in Hibernate
Spatial. They are currently registered into each concrete SpatialDialect. I
think it might be a good start to start having these functions integrated into
HQL.
These functions are commonly found in spatial databases because they have been
defined in the Simple Feature Specification (SFS). The reference given after
each function refers to this spec. This spec was originally intended to be used
only for planar 2D geometries, but has been extended by most databases to apply
also to 3D/4D and non-planer, i.e. geographic coordinates.
There is also the 'SQL/MM, Part 3' - Spatial specification. This spec is, as I
understand it, derived from the Simple Feature Specification but adds support
for more complicated geometries and for 3D/4D geometries. Not all databases
have support for everything specified in there, and no open-source Java
geometry library has either.
As for implementation, there are some weird cases. For example, if you specify
in MySQL (native SQL) "select * from t where st_contains(geom1, geom2) = 1”
the spatial query is not used, but it is used when the statement reads "select
* from t where st_contains(geom1, geom2)”. Both should be equivalent.
Another example. In Oracle10g the HQL spatial functions are translated to
something like this: "SELECT A.Feature_ID FROM TARGET A WHERE
sdo_filter(A.shape, :theWindow,'querytype=window') = 'TRUE’;”
The whole and only the whole expression ‘sdo_filter(...) = ‘TRUE’’ evaluates to
TRUE. So leaving the “... = ‘TRUE’” part off or putting something else in
there, fails to evaluate.
Hope this helps kick off the discussion.
Regards,
Karel
> On 26 Aug 2015, at 05:20, Steve Ebersole <st...@hibernate.org> wrote:
>
> Karel, etal
>
> We have discussed spatial-specific extensions to HQL for quite some time.
> But those discussions have always been kind of esoteric ("boy wouldn't it
> be nice to have some spatial support in HQL").
>
> As we are working on redesigning the parsing and interpretation of HQL
> queries and since spatial has been integrated upstream, it seems like a
> great time to discuss specifics of what this might mean.
>
> I have never used spatial data, let alone crafted queries using spatial
> data. So I am not the best driver here.
>
> What kinds of things make sense to add to HQL for supporting spatial
> queries?
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