PostGIS Dialect Uses Old Function Name for Spatial Extent
The PostGIS dialect uses "extent" as the function name for the aggregated spatial extent, on lines 209 and 306 of PostgisDialect.java. PostGIS recommended using the "st_" versions around 1.2.2, and support for the non-"st_" versions was dropped somewhere between 1.4 and 2.0. Also, every other function in PostgisDialect.java begins with "st_".
Given that Hibernate Spatial 4+ appears to be primarily a compatibility update with new[er] versions of Hibernate, I recommend using the spatial extent function name that has been recommended since PostGIS 1.2. I think it reasonable to expect those still using PostGIS 1.1.x to continue to use Hibernate Spatial 1.x. But I suspect I am not the only one who would like to upgrade PostGIS to something recent at the same time that I'm upgrading Hibernate to something recent.