http://qs321.pair.com?node_id=317422

arc_of_descent has asked for the wisdom of the Perl Monks concerning the following question:

Hello Dear Monks

I'm having some trouble setting up a has_many relationship between 2 entities - a page entity and a column entity. The relationship I'm tring to use in my code is 'a page has many columns'.

If I structure the tables in the following way, I'm facing no problems.

Table page
page_id page_title
1 Geography
2 History
Table column
column_id column_title page_id
1 Geog 1 1
2 Geog 2 1
3 Geog 3 1
4 Hist 1 2

I set up all the DBI modules, etc... and in Page.pm I add a line:

__PACKAGE__->has_many(cols => 'Column');

Now I can get all columns of a page with the following code:

$columns = Page->retrieve(1)->cols;

Now good database design, has taught me that when one has a 1:N relationship, one should construct a new table to hold that relationship.
So, the foll structure:
Table page
page_id page_title
1 Geography
2 History
Table page_column
page_id column_id
1 1
1 2
1 3
2 4
Table column
column_id column_title
1 Geog 1
2 Geog 2
3 Geog 3
4 Hist 1

So now how do I code the relationships in my Class::DBI modules which would enable me to get all the columns of a page in the same was as above.
i.e.

$columns = Page->retrieve(1)->cols;

Thankz in advance for all suggestions and help and compliments of the season to all of you!

update:
Changed the 'columns' method to 'cols' since Class::DBI already has a 'columns' method
- Thanks to PodMaster