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.\" ========================================================================
.\"
.IX Title "DBI::DBD::Metadata 3"
.TH DBI::DBD::Metadata 3 "2021-08-09" "perl v5.32.1" "User Contributed Perl Documentation"
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.nh
.SH "NAME"
DBI::DBD::Metadata \- Generate the code and data for some DBI metadata methods
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
The idea is to extract metadata information from a good quality
\&\s-1ODBC\s0 driver and use it to generate code and data to use in your own
\&\s-1DBI\s0 driver for the same database.
.PP
To generate code to support the get_info method:
.PP
.Vb 1
\&  perl \-MDBI::DBD::Metadata \-e "write_getinfo_pm(\*(Aqdbi:ODBC:dsn\-name\*(Aq,\*(Aquser\*(Aq,\*(Aqpass\*(Aq,\*(AqDriver\*(Aq)"
\&
\&  perl \-MDBI::DBD::Metadata \-e write_getinfo_pm dbi:ODBC:foo_db username password Driver
.Ve
.PP
To generate code to support the type_info method:
.PP
.Vb 1
\&  perl \-MDBI::DBD::Metadata \-e "write_typeinfo_pm(\*(Aqdbi:ODBC:dsn\-name\*(Aq,\*(Aquser\*(Aq,\*(Aqpass\*(Aq,\*(AqDriver\*(Aq)"
\&
\&  perl \-MDBI::DBD::Metadata \-e write_typeinfo_pm dbi:ODBC:dsn\-name user pass Driver
.Ve
.PP
Where \f(CW\*(C`dbi:ODBC:dsn\-name\*(C'\fR is the connection to use to extract the
data, and \f(CW\*(C`Driver\*(C'\fR is the name of the driver you want the code
generated for (the driver name gets embedded into the output in
numerous places).
.SH "Generating a GetInfo package for a driver"
.IX Header "Generating a GetInfo package for a driver"
The \f(CW\*(C`write_getinfo_pm\*(C'\fR in the DBI::DBD::Metadata module generates a
DBD::Driver::GetInfo package on standard output.
.PP
This method generates a DBD::Driver::GetInfo package from the data
source you specified in the parameter list or in the environment
variable \s-1DBI_DSN.\s0
DBD::Driver::GetInfo should help a \s-1DBD\s0 author implement the \s-1DBI\s0
\&\fBget_info()\fR method.
Because you are just creating this package, it is very unlikely that
DBD::Driver already provides a good implementation for \fBget_info()\fR.
Thus you will probably connect via \s-1DBD::ODBC.\s0
.PP
Once you are sure that it is producing reasonably sane data, you should
typically redirect the standard output to lib/DBD/Driver/GetInfo.pm, and
then hand edit the result.
Do not forget to update your Makefile.PL and \s-1MANIFEST\s0 to include this as
an extra \s-1PM\s0 file that should be installed.
.PP
If you connect via \s-1DBD::ODBC,\s0 you should use version 0.38 or greater;
.PP
Please take a critical look at the data returned!
\&\s-1ODBC\s0 drivers vary dramatically in their quality.
.PP
The generator assumes that most values are static and places these
values directly in the \f(CW%info\fR hash.
A few examples show the use of \s-1CODE\s0 references and the implementation
via subroutines.
It is very likely that you will have to write additional subroutines for
values depending on the session state or server version, e.g.
\&\s-1SQL_DBMS_VER.\s0
.PP
A possible implementation of \fBDBD::Driver::db::get_info()\fR may look like:
.PP
.Vb 7
\&  sub get_info {
\&    my($dbh, $info_type) = @_;
\&    require DBD::Driver::GetInfo;
\&    my $v = $DBD::Driver::GetInfo::info{int($info_type)};
\&    $v = $v\->($dbh) if ref $v eq \*(AqCODE\*(Aq;
\&    return $v;
\&  }
.Ve
.PP
Please replace Driver (or \*(L"<foo>\*(R") with the name of your driver.
Note that this stub function is generated for you by write_getinfo_pm
function, but you must manually transfer the code to Driver.pm.
.SH "Generating a TypeInfo package for a driver"
.IX Header "Generating a TypeInfo package for a driver"
The \f(CW\*(C`write_typeinfo_pm\*(C'\fR function in the DBI::DBD::Metadata module generates
on standard output the data needed for a driver's type_info_all method.
It also provides default implementations of the type_info_all
method for inclusion in the driver's main implementation file.
.PP
The driver parameter is the name of the driver for which the methods
will be generated; for the sake of examples, this will be \*(L"Driver\*(R".
Typically, the dsn parameter will be of the form \*(L"dbi:ODBC:odbc_dsn\*(R",
where the odbc_dsn is a \s-1DSN\s0 for one of the driver's databases.
The user and pass parameters are the other optional connection
parameters that will be provided to the \s-1DBI\s0 connect method.
.PP
Once you are sure that it is producing reasonably sane data, you should
typically redirect the standard output to lib/DBD/Driver/TypeInfo.pm,
and then hand edit the result if necessary.
Do not forget to update your Makefile.PL and \s-1MANIFEST\s0 to include this as
an extra \s-1PM\s0 file that should be installed.
.PP
Please take a critical look at the data returned!
\&\s-1ODBC\s0 drivers vary dramatically in their quality.
.PP
The generator assumes that all the values are static and places these
values directly in the \f(CW%info\fR hash.
.PP
A possible implementation of \fBDBD::Driver::type_info_all()\fR may look like:
.PP
.Vb 5
\&  sub type_info_all {
\&    my ($dbh) = @_;
\&    require DBD::Driver::TypeInfo;
\&    return [ @$DBD::Driver::TypeInfo::type_info_all ];
\&  }
.Ve
.PP
Please replace Driver (or \*(L"<foo>\*(R") with the name of your driver.
Note that this stub function is generated for you by the write_typeinfo_pm
function, but you must manually transfer the code to Driver.pm.
.SH "AUTHORS"
.IX Header "AUTHORS"
Jonathan Leffler <jleffler@us.ibm.com> (previously <jleffler@informix.com>),
Jochen Wiedmann <joe@ispsoft.de>,
Steffen Goeldner <sgoeldner@cpan.org>,
and Tim Bunce <dbi\-users@perl.org>.
