Let me first answer your question directly and then suggest an
alternative.
First of all, let’s follow rails convention here and create two
tables: entities and entity_integers. We’ll also create the models
that rails will use to interface them. We’ll do both at once with:
ruby script/generate model Entity
ruby script/generate model EntityInteger
You will find two new migrations in db/migrate:
001_create_entities.rb
002_create_entity_integers.rb
In those add your columns:
class CreateEntities < ActiveRecord::Migration
def self.up
create_table :entities do |t|
t.column :title, :string
end
end
def self.down
drop_table :entities
end
end
Similarly in your 002_create_entity_integers.rb migration add:
t.column :value, :integer
t.column :entity_id, :integer
in your Entity model (app/models/entity.rb) add:
has_many :entity_integers
and in your EntityInteger model add:
belongs_to :entity
Run rake db:migrate and that’s it. open up script/console and play
around.
@entity = Entity.new :title => “foo”
@entity.save
@entity.entity_integers.create :value => 1
@entity.entity_integers.create :value => 2
@entity.entity_integers.map {|integer| integer.value} #=> [1, 2]
Now here’s an alternative. Create the same Entity model as before but
in the migration do:
t.column :title, :string
t.column :integrers, :string, :default => [].to_yaml # will work in
MySQL but not Postgres, last time I checked.
and in the Entity model:
seialize :integers, :class_name => Array
and try this out:
@entity = Entity.new :title => “foo”
@entity.integers += [1,2,3]
@entity.save
@entity.integers #=> [1,2,3]
@entity.integers += [5,6,7]
@entity.save
@entity.integers #=> [1,2,3,5,6,7]
Now @entity.integers is transparently serialized into the database as
an array.
Just another option.
Rein
