Re: JDBC pg_description update needed for CVS tip

Attached is the patch requested by Tom Lane (see below). It
includes two changes in the JDBC driver:

1) When connected to a backend >= 7.2: use obj_description() and
col_description() instead of direct access to pg_description.

2) In DatabaseMetaData.getTables()/getColumns()/getProcedures():
when there is no comment on the object, return null in the
REMARKS column of the ResultSet, instead of the default string
"no remarks".

Change 2 first appeared as a side-effect of change 1, but it is
actually more compliant with the JDBC spec: "String object
containing an explanatory comment on the table/column/procedure,
which may be null". The default string "no remarks" was strictly
speaking incorrect, as it could not be distinguished from a real
user comment "no remarks". So I removed the default string
completely.

Change 2 might break existing code that doesn't follow the JDBC
spec and isn't prepared to handle a null in the REMARKS column
of getTables()/getColumns()/getProcedures.

Patch tested with jdbc2 against both a 7.1 and a CVS tip
backend. I did not have a jdbc1 environment to build and test
with, but since the touched code is identical in jdbc1 and jdbc2
I don't foresee any problems.

Regards,
René Pijlman

On Fri, 10 Aug 2001 16:08:50 -0400, Tom Lane wrote:
>Would some JDBC hacker develop a patch for the following issue? The
>change is just barely large enough that I don't want to commit untested
>code for it --- but not having a Java development environment at hand,
>I can't test the updated code.
>
>The problem is in DatabaseMetaData.java (same code in both jdbc1 and
>jdbc2, looks like). It does direct access to pg_description that isn't
>right anymore. In getTables, instead of
>
> java.sql.ResultSet dr = connection.ExecSQL("select description from pg_description where objoid="+r.getInt(2));
>
>it should be
>
> java.sql.ResultSet dr = connection.ExecSQL("select obj_description("+r.getInt(2)+",'pg_class')");
>
>In getColumns, the change is a little more involved, because
>pg_attribute doesn't have an OID column anymore. The initial query
>can't fetch a.oid, but should fetch a.attrelid instead, and then the
>pg_description query should become
>
> java.sql.ResultSet dr = connection.ExecSQL("select col_description("+r.getInt(1)+","+r.getInt(5)+")");
>
>(col_description takes the table OID and the column's attnum).
>
>The reason this is more than a 3-line change is that it should be done
>either the old way or the new way depending on whether server version >=
>7.2 or not, for backwards-compatibility of the driver.
>
>It's possible there are other similar changes needed that I missed in a
>quick lookover.
>
>So, would some enterprising person fix the JDBC code to work with CVS
>tip, and submit a patch?
>
> thanks, tom lane
>
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Regards,
René Pijlman