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From "Dag H. Wanvik" <Dag.Wan...@Sun.COM>
Subject Re: [jira] Created: (DERBY-447) getBoolean() throws data conversion exception for DECIMAL type in J2ME/CDC/Foundation
Date Fri, 08 Jul 2005 22:53:44 GMT

Hi,

(Lance, see question to you below)

>>>>> "DJD" == Daniel John Debrunner <djd@debrunners.com> wrote:
DJD> 
DJD> Dag H. Wanvik wrote:
DJD> > DJD> There's some inconsistency here, the ResultSet getter methods are
DJD> > DJD> converting from SQL data types to Java data types. This supportsConvert
DJD> > DJD> method takes two arguments, both of which describe SQL data types.
DJD> > 
DJD> > Yes, you are right. Something for Lance to clarify :) 
DJD> > But it would seem the no-args supportsConvert() should return false
DJD> > until we add support for CONVERT.
DJD> 
DJD> And just to be clear, this is the JDBC CONVERT function from section C.5
DJD> of JDBC 3.0, correct?

Yes. 

DJD> 
DJD> I think there is some issue with CONVERT in JDBC 4.0, where the format
DJD> of the second argument is changing, from INTEGER to SQL_INTEGER or
DJD> something like that?

Hmm.. I did a short check..  The DataBaseMetaData.supportsConvert has
int (from java.sql.Types aka JDBC types/SQLtypes) for both arguments
(both in JDBC 3.0 and early draft 4.0), which makes sense since the
API speaks of describing the support/behavior of CONVERT, and this
conversion all happens in the SQL domain.

[On a side note: actually the Javadoc for supportsConvert speaks of
(unqualified) CONVERT, without being explicit on this being the C.5
escape JDBC CONVERT, not the SQL character set CONVERT, but I guess
that's kind of obvious..?]

Also, in both the JDBC 3.0 and 4.0 spec, the escape function CONVERT
has SQLtype as the second argument, "value" being given as the first.

The PreparedStatement "setter"/ ResultSet "getter" functions mappings,
though, convert from and to Java types, given by the tables in the B
appendix.

I think the problem is that section 15.2.3.1 in the JDBC 4.0 spec
(14.2.3.1 in 3.0) erroneously states that
DataBaseMetaData.supportsConvert says ANYTHING about the mapping for
getter methods. Interestingly, the corresponding section on conversion
for *setter* methods makes no mention of
DataBaseMetaData.supportsConvert (section 13.2.2.1 in 4.0 as well as
in 3.0). Nor do the IN, OUT, INOUT descriptions.

> 15.2.3.1 Data Type Conversions
> The recommended ResultSet getter method for each JDBC type is shown
> in TABLE B-6 on page B-210. This table also shows all of the
> possible conversions that a JDBC driver may support. The method
> DataBaseMetaData.supportsConvert(int fromType, int toType) returns
************************************ 
> true if the driver supports the given conversion.

Lance, do you agree this is wrong? If it is correct, please explain
what I am missing here..!

Notwhithstanding this, the Derby implementation of no-args
DataBaseMetaData.supportsConvert() returns true, indicating we support
C.5 CONVERT, which we do not AFAICS, and I suggest we make a JIRA for
that.

Dag

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