How can I do a SQL query to an Oracle database with Perl and get the result as JSON? - sql

Question

I'm working with a legacy system and need to get data out of an Oracle database using Perl. Perl is one of the languages I don't spend much time in, so I'd like to be able to run a simple SQL query and pass the data to another system via JSON.
It seems that JSON, DBI, and DBD are available on this system. I'd like to accomplish this without making too many changes or updates to the system, if possible. I believe the JSON library is at version 5.12.2
I found DBI-Link library on Github and I believe this file is almost exactly what I need:
#!/usr/bin/perl -l
use strict;
use warnings;
$|++;
use JSON;
use DBI;
use DBD::Oracle qw(:ora_types);
my $dbh = DBI->connect(
'dbi:Oracle:host=localhost;sid=xe',
'hr',
'foobar',
{
AutoCommit => 1,
RaiseError => 1,
}
);
my #methods = qw(table_info column_info primary_key_info);
foreach my $method (#methods) {
if ( $dbh->can($method) ) {
print "Handle has method $method. w00t!"
}
else {
$dbh->disconnect;
print "Sadly, handle does not have method $method. D'oh!";
exit;
}
}
my $sth=$dbh->table_info('%', '%', '%', 'TABLE');
while(my $table = $sth->fetchrow_hashref) {
my $t;
$t->{'Table Name'} = $table->{TABLE_NAME};
$t->{'Column Info'} = $dbh->column_info(
undef,
$table->{TABLE_SCHEM},
$table->{TABLE_NAME},
'%'
)->fetchall_arrayref({});
$t->{'Primary Key Info'} = $dbh->primary_key_info(
undef,
$table->{TABLE_SCHEM},
$table->{TABLE_NAME}
)->fetchall_arrayref({});
print map {"$_: ". json_encode($t->{$_})} grep{ defined $t->{$_} } 'Table Name', 'Column Info', 'Primary Key Info';
print;
}
$sth->finish;
$dbh->disconnect;
The Error
I've installed the dependencies but when I run it I am getting:
Undefined subroutine &main::json_encode called at ./oracle.t line 47.
I searched the rest of the source in that repository and don't see any my json_encode definition, so maybe I have a version of the JSON library that is too old is my possible idea, but it seems unlikely that the json_encode method would have changed names.
The Next Steps
After I get json_encode to work I know I will need to execute a custom query and then save the data, it would be something like this:
$sth = $dbh->prepare("select * from records where pending = 1");
$sth->execute;
my $records = new HASH;
while($r = $sth->fetchrow_hashref)
{
$records << $r
}
my $json = json_encode($records)
However I'm unsure how to build the $records object for encoding so any help would be appreciated. I have searched stackoverflow, google, and github for perl examples of oracle to json and only had luck with the code from that DBI-Link repo.

Answer 1

According to the documentation for the JSON module, the function you want is encode_json and not json_encode.
I'd probably store the records in an array of hashes; something like this:
my #records;
while (my $r = $sth->fetchrow_hashref)
{
push(#records, $r);
}
If you know what field you want a hash-of-hashes keyed on:
my %records;
while (my $r = $sth->fetchrow_hashref)
{
$records{ $r->{key_field} } = $r;
}