Foreign-key confusion


#1

Hi,

I am a bit confused about managing the relationship between two of my
tables:

I have developed a script using scRUBYt that scrapes data from a website
and dumps the following four fields into my Shows table:

class CreateShows
create table :shows do |t|
t.string :date
t.string :venue
t.string :info
t.string :comics

The second table I created is called Theatres:

class CreateTheatres
create table :theatres do |t|
t.string :name
t.string :address
t.string :website_url
t.string :location

The :venue field in the Shows table corresponds to the :name field in
the Theatres table. How do I set up a relationship whereby Theatres have
many shows, while defining this (:venue - :name) relationship as the
link?

I have tried the :set_primary_key & :foreign_key => … methods without
success.
Does the primary or foreign key always have to be an integer?

Any suggestions would be much appreciated…


#2

On 21 Feb 2009, at 13:22, Ad Richards wrote:

class CreateShows
t.string :name
I have tried the :set_primary_key & :foreign_key => … methods
without
success.
Does the primary or foreign key always have to be an integer?

A belongs_to relationship has to go through the primary key of the
other model and setting the primary key of theatres to be the name
would be a bad thing (eg what if two towns had a theatre by the same
name).
The rails way would be to do away with the venue column and have a
theatre_id one instead


#3

Thanks Fred,

I took your advice and added a theatre_id column to the Shows table.

Then I added the following callback to the Shows model, in order to
automatically update the :theatre_id column with the id of the
corresponding theatre in the Theatres table.

class Show < ActiveRecord::Base
belongs_to :theatre

after_create :build_theatre_ids

def build_theatre_ids
t = Theatre.find_by_name(self.venue)
self.update_attributes(:theatre_id => t.id) rescue nil
end
end

And it works a treat!