Relating ID's in relational table - sql

Question

I have these two insertion queries in Perl using the DBI module and DBD:mysql.
This one inserts fields url, html_extr_text, concord_file, and sys_time into table article:
my #fields = (qw(url html_extr_text concord_file sys_time));
my $fieldlist = join ", ", #fields;
my $field_placeholders = join ", ", map {'?'} #fields;
my $insert_query = qq{
INSERT INTO article ($fieldlist)
VALUES ($field_placeholders)
};
my $sth = $dbh->prepare($insert_query);
my $id_article;
my #id_articles;
foreach my $article_index (0 .. #output_concord_files_prepare) {
$field_placeholders = $sth->execute(
$url_prepare[$article_index],
$html_pages_files_extended[$article_index],
$output_concord_files_prepare[$article_index],
$sys_time_prepare[$article_index]);
$id_article = $dbh->last_insert_id(undef, undef, 'article', 'id_article');
push #id_articles, $id_article;
if ($field_placeholders != 1) {
die "Error inserting records, only [$field_placeholders] got inserted: " . $sth->insert->errstr;
}
}
print "#id_articles\n";
And this one inserts field event into table event:
#fields = (qw(event));
$fieldlist = join ", ", #fields;
$field_placeholders = join ", ", map {'?'} #fields;
$insert_query = qq{
INSERT INTO event ($fieldlist)
VALUES ($field_placeholders)
};
$sth = $dbh->prepare($insert_query);
my $id_event;
my #id_events;
foreach my $event_index (0 .. #event_prepare){
$field_placeholders = $sth->execute($event_prepare[$event_index]);
$id_event = $dbh->last_insert_id(undef, undef, 'event', 'id_event');
push #id_events, $id_event;
if ($field_placeholders != 1){
die "Error inserting records, only [$field_placeholders] got inserted: " . $sth->insert->errstr;
}
}
print "#id_events\n";
I'd like to create a third one-to-many relationship table. Because, one article contains multiple events, so I have this file :
output_concord/concord.0.txt -> earthquake
output_concord/concord.0.txt -> avalanche
output_concord/concord.0.txt -> snowfall
output_concord/concord.1.txt -> avalanche
output_concord/concord.1.txt -> rock fall
output_concord/concord.1.txt -> mud slide
output_concord/concord.4.txt -> avalanche
output_concord/concord.4.txt -> rochfall
output_concord/concord.4.txt -> topple
...
As you can see, I collect the IDs of each entry using the LAST_INSERT_ID. However I don't really know how to make the next step.
Using this file, how can I insert into a third table 'article_event_index' the ids of the two previous tables.
It would be something like this:
$create_query = qq{
create table article_event_index(
id_article int(10) NOT NULL,
id_event int(10) NOT NULL,
primary key (id_article, id_event),
foreign key (id_article) references article (id_article),
foreign key (id_event) references event (id_event)
)
};
$dbh->do($create_query);
Which will contain relationships following the pattern
1-1, 1-2, 1-3, 2-4, 3-5 ...
I'm a newbie to Perl and databases so it's hard to formulate what I want to do. I hope I was clear enough.

Answer 1

Something like this should do what you need (untested, but it does compile).
It starts by building Perl hashes to relate concord files to article IDs and events to event IDs. Then the file is read, and a pair of IDs is inserted into the new table for each relationship that can be found in the exisiting tables.
Note that the hashes are there only to avoid a long sequence of
SELECT id_article FROM article WHERE concord_file = ?
and
SELECT id_event FROM event WHERE event = ?
statements.
use strict;
use warnings;
use DBI;
use constant RELATIONSHIP_FILE => 'relationships.txt';
my $dbh = DBI->connect('DBI:mysql:database', 'user', 'pass')
or die $DBI::errstr;
$dbh->do('DROP TABLE IF EXISTS article_event_index');
$dbh->do(<< 'END_SQL');
CREATE TABLE article_event_index (
id_article INT(10) NOT NULL,
id_event INT(10) NOT NULL,
PRIMARY KEY (id_article, id_event),
FOREIGN KEY (id_article) REFERENCES article (id_article),
FOREIGN KEY (id_event) REFERENCES event (id_event)
)
END_SQL
my $articles = $dbh->selectall_hashref(
'SELECT id_article, concord_file FROM article',
'concord_file'
);
my $events = $dbh->selectall_hashref(
'SELECT id_event, event FROM event',
'event'
);
open my $fh, '<', RELATIONSHIP_FILE
or die sprintf qq{Unable to open "%s": %s}, RELATIONSHIP_FILE, $!;
my $insert_sth = $dbh->prepare('INSERT INTO article_event_index (id_article, id_event) VALUES (?, ?)');
while (<$fh>) {
chomp;
my ($concord_file, $event) = split /\s*->\s*/;
next unless defined $event;
unless (exists $articles->{$concord_file}) {
warn qq{No article record for concord file "$concord_file"};
next;
}
my $id_article = $articles->{$concord_file}{id_article};
unless (exists $events->{$event}) {
warn qq{No event record for event "$event"};
next;
}
my $id_event = $events->{$event}{id_event};
$insert_sth->execute($id_article, $id_event);
}