On Sun, Feb 14, 2021 at 5:23 AM Tom Lane <t...@sss.pgh.pa.us> wrote: > Patrick Handja <patrick.bung...@gmail.com> writes: > > I would like to know if there is a better way to pass a relation or if > the > > relation name (CString) as a parameter in a C function and thus be able > to > > manipulate its tuples. The documentation is available here: > > https://www.postgresql.org/docs/13/xfunc-c.html#id-1.8.3.13.11. But it > is > > not quite clear enough on how to retrieve tuples. > > The thing I'd recommend you do is use SPI [1], which lets you execute > SQL queries from inside a C function. If you don't want to do that > for whatever reason, you need to open the relation, set up a scan, > and fetch tuples from the scan, relying on low-level APIs that tend > to change from version to version. contrib/pageinspect or > contrib/pgstattuple might offer usable sample code, although with any > prototype you might look at, it's going to be hard to see the forest > for the trees. > > regards, tom lane > > [1] https://www.postgresql.org/docs/current/spi.html > > > Thank you tom for the reply. What would be the difference between the SPI and "write a pure SQL UDF" and call it with DirectFunctionCall1? I just ran into a similar situation some days before. Currently I think DirectFunctionCall1 doesn't need to maintain a connection but SPI has to do that.
-- Best Regards Andy Fan (https://www.aliyun.com/)
