[hibernate-dev] HQL and spatial

[Karel Maesen]

Hi Steve,

> On 08 Sep 2015, at 22:29, Steve Ebersole <steve at hibernate.org> wrote:
> 
> What do you mean "have these functions integrated into HQL"?  What you describe is exactly how sql functions are supported as well.  Perhaps you mean defining standard support for spatial functions.  

Yes, precisely that

> As a corollary, take something like the ANSI SQL TRIM function.  Not all databases support TRIM as defined by ANSI SQL so ultimately we leverage Dialect registered support for what the database does support.  However, we encode "TRIM support" into the HQL grammar (in the rewrite) to make sure that the arguments are handled consistently.  We do still expect each that the Dialect as registered an appropriate SQLFunction representation of its TRIM function support.  We could do something like that here as well.  The main difference is that not all applications are using spatial.

It is true that not all applications use spatial, or even that DB’s support (all) spatial functions. But it would help to ensure consistency in the available dialects. Now this consistency is tested for in the integration tests, so not having this at the grammar isn’t a big problem. 

> 
> So more I am asking about syntax changes that might help support spatial queries, specific operators, etc.  How about declaring "spatial literals"?  Does that make sense for spatial queries?

W.r.t operators: don’t the same concern about not all applications using spatial apply here as well? In any case, I don’t think operators are going to be popular. Just about everyone is happy to use the relevant spatial relationship functions. At least their names and semantics are pretty standard across implementations and technologies. There is to my knowledge no comparable standard for spatial symbolic operators.

Support for spatial literals would be a great plus. In my opinion, the best candidate for HQL spatial literals is the Postgis EWKT format (http://postgis.net/docs/manual-2.1/using_postgis_dbmanagement.html#EWKB_EWKT), which is a sane, and popular extension of the purely 2D WKT standard. It is  supported in the geolatte-geom library and many others. I can help by writing a grammar for this.

There is also at least one HQL syntax change that would help implement spatial functions:  function invocations that evaluate to boolean should be regarded as valid boolean expressions. The HQL currently doesn’t seem to allow this, so I needed to wrap them in equality expressions. But then MySQL wouldn’t use its spatial index (as I wrote before, although I mistakenly wrote “spatial query” in my original email).

Regards,

Karel