Re: Transaction processing from a Perl script.... - Mailing list pgsql-general

Greg Patnude wrote:
> Ok.... I can connect to my postgreSQL database with Autocommit=>0 to set
> up for a transaction-based process...I'm using Perl 5.6 and Pg 1.9 on a
> FreeBSD 4.x box with postgreSQL 7.2.

First off I'd suggest using DBI and DBD::Pg instead of the Pg module

> Usually, this kind of thing is handled by the connect method (I've
> typically used Oracle, Sybase, or SQL Server with VB, C, or Powerbuilder)
> and the
> {begin {process}{commit or rollback}} is managed by the connect method
> defined in the application. Pg has no such mechanism that I could find in
> the Pg docs...

DBI is the standard 'DataBase Interface' for Perl (think: ODBC, JDBC).
It probably handles things in the way you're more familiar with.

It automatically starting transactions (at connection and after a
commit/rollback a new one is started) and will automatically die (if
using RaiseError => 1) on an error.

> The question is HOW should I go about managing the transaction itself from
> within my Perl script... I need to {pseudo}:
>
> --begin work
> --insert into child table 1 (and return the new primary key pk1)
> --insert into child table 2 (and retrun the new primary key pk2)
> --insert into the master table (child 1 pk, child 2 pk) and return the
> master primary key pkm
> --commit work if everything is ok
> --else rollback if anything failed.

The following code shell should get you started (it has graceful error
catching):


    #!/usr/bin/perl
    use strict;
    use warnings;

    use DBI;
    use Error;

    ...

    my $dbh = DBI->connect('con_str', 'user', 'passwd', {
        AutoCommit => 0,
        RaiseError => 1,
    }) or die "Could not establish connection: $!";

    ...

    try {
        my $sth = $dbh->prepare(q{
            INSERT INTO table (field1, ... fieldn)
            VALUES (?, ...?)
        });

        $sth->execute($foo, $bar);

        ...

        $dbh->commit;
    }
    catch Error {
        $dbh->rollback;
        die "Failure on $err";
    };

The above example is generalised to any DBMS with a DBD driver written
for it. As you can see DBI includes placeholder, automatic error
throwing, and a common syntax across DBMSs (SQL dialects are unchanged
ofcourse).

(There are also PostgreSQL specific attributes, see DBD::Pg
documentation for more info.)

The try/catch syntactical sugar is provided by the Error module, which
is by no means limited to the simplistic use shown here. If you don't
want to use a module, the form...

    eval    { code goes here }
    if (@!) { error handling here }

... is straight base Perl.


Read up on the below documentation for more precise information.


SEE ALSO:

DBI     - http://search.cpan.org/author/TIMB/DBI-1.30/DBI.pm
DBD::Pg - http://search.cpan.org/author/JBAKER/DBD-Pg-1.13/Pg.pm
Error   -
http://search.cpan.org/author/BIRNEY/bioperl-1.0.2/examples/exceptions/Error.pm