DOC: Add list of keys for proj_context_get_database_metadata

[snowman2]

It would be useful to be able to get the database version of EPSG|ESRI|etc. through the C-API for informational purposes. That way the user can see what version(s) the current PROJ database is using.

[rouault]

This is covered by using proj_context_get_database_metadata and querying the keys of https://github.com/OSGeo/PROJ/blob/master/data/sql/metadata.sql

[snowman2]

Perfect! Thanks 👍

[snowman2]

Reopening because it is missing the ESRI database version in there. Any other database versions that would be good to add?

[snowman2]

Looks like ESRI 12.8? #2717

[rouault]

The ESRI specific metadata is set in https://raw.githubusercontent.com/OSGeo/PROJ/master/data/sql/esri.sql
Simlarly for https://raw.githubusercontent.com/OSGeo/PROJ/master/data/sql/ignf.sql
Perhaps those known keys should be documented in proj_context_get_database_metadata()

[snowman2]

Would it make sense to move the versions to sql/metadata.sql and add a note in the other files to update sql/metadata.sql?

[rouault]

Would it make sense to move the versions to sql/metadata.sql and add a note in the other files to update sql/metadata.sql?

the versions set in esri.sql and ignf.sql are done by their respective import scripts. I believe it is better if the import script set the versions as part as the import process to avoid (forgetting to) updating them manually.

[snowman2]

Makes sense to me. I updated the issue title.