Hi David,
"Catalog" is an undefined term for Derby. In contrast, for another open
source database, MySQL, "catalog" means "database". MySQL seems to have
a concept of "databases managed by this server". Derby does not.
A Derby database can live anywhere in the file system and can be managed
by any Derby engine running on the machine. You could speak of
"databases potentially managed by this engine". Computing that list
might mean scanning the entire file system which the engine has
permission to read--and even looking inside all of the visible jar files
since a read-only Derby database can be stored in a jar file. We might
be able to give a well-defined meaning to "databases potentially managed
by Derby", but I suspect that the devil is in the details.
You could also speak about "databases currently managed by this engine".
That could mean all of the databases currently booted by a given Derby
engine. That meaning seems limited and well-defined to me but I don't
think it maps exactly to what another RDBMS might mean by "catalog".
What would you like "catalog" to mean for Derby?
Here are the results of the getCatalogs() and getCatalogTerm() calls for
a Derby engine and a MySQL server. Here I am using the DBMDWrapper
functions attached to DERBY-3973:
ij> -- Derby's list of catalogs
select * from table( getCatalogs() ) s;
TABLE_CAT
--------------------------------------------------------------------------------------------------------------------------------
0 rows selected
ij> -- Derby's preferred term for catalog
values ( getCatalogTerm() );
1
--------------------------------------------------------------------------------------------------------------------------------
CATALOG
1 row selected
ij> -- now ask MySQL the same questions
call setDatabaseURL( 'com.mysql.jdbc.Driver',
'jdbc:mysql://localhost/world?user=root&password=' );
0 rows inserted/updated/deleted
ij> -- MySQL's list of catalogs
select * from table( getCatalogs() ) s;
TABLE_CAT
--------------------------------------------------------------------------------------------------------------------------------
information_schema
mysql
test
world
4 rows selected
ij> -- MySQL's preferred term for catalog
values ( getCatalogTerm() );
1
--------------------------------------------------------------------------------------------------------------------------------
database
1 row selected
ij> -- release the MySQL connection
call setDatabaseURL( '', '' );
0 rows inserted/updated/deleted
Hope this helps,
-Rick
Lance J. Andersen wrote:
Depends on the concept in Derby of what a catalog is as your mileage
can vary between databases.
Some vendors treat it as the database name, others do not.
Null is allowed to be returned if the concept of catalog is not
applicable to a given database
Regards
Lance
David Van Couvering wrote:
Shouldn't Connection.getCatalog() return the name of the database you
are connected to, and shouldn't DMD.getCatalogs() return a result set
with one row, representing the database you're connected to?
This is causing us a bit of a headache when we're trying to inspect a
Derby database in NetBeans...
Thanks,
David
--
David W. Van Couvering
http://davidvancouvering.blogspot.com
