On 3/27/07, Robert James Kaes [EMAIL PROTECTED] wrote:
CREATE TABLE locations (
id INT,
...);
CREATE TABLE companies (
id INT,
location_id INT NOT NULL REFERENCES locations(id),
...);
CREATE TABLE exhibitions (
id INT,
location_id INT NOT NULL REFERENCES locations(id),
...);
[...] What I'd like to create is a company relationship in Exhibition that
returns the Company that has the same location_id as itself.
Given the schema above, there could be many such companies, not just
one. So it'd be a one-to-many relationship:
package Exhibition;
...
__PACKAGE__-meta-setup(
...
relationships =
[
companies =
{
type = 'one to many',
class = 'Company',
column_map = { location_id = location_id },
},
...
You'll get a list or reference to an array of related companies
through this method:
$e = Exhibition-new(id = ...)-load;
$companies = $e-companies;
if(@$companies) { ... }
If there really can only be one such company with the same location
id, then you'll have to make location_id a unique key of the companies
table and/or Company class:
package Company;
...
__PACKAGE__-meta-setup(
...
unique_key = 'location_id',
...
then set up a many-to-one relationship like this:
package Exhibition;
...
__PACKAGE__-meta-setup(
...
relationships =
[
company =
{
type = 'many to one',
class = 'Company',
column_map = { location_id = location_id },
required = 0,
},
...
The required attribute makes the method return undef (instead of
throwing an exception) when no matching company exists:
http://search.cpan.org/dist/Rose-DB-Object/lib/Rose/DB/Object/Metadata/Relationship/ManyToOne.pm#required
$company = $e-company; # may be undef
-John
-
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