Well, I don't have an actual answer for you. But.....
Why, oh why, are you using composite primary keys if you're creating the table? I can certainly see having the need with legacy databases, where you have no control over the design. However, given that you are showing a migration in your original post, then why are you making your life unnecessarily complicated?
Why not just give Rails its simple integer primary key? Rails will be happier, you will be happier, in the long run, and all will be right with the world.
Now don't get me wrong, there may be a perfectly reasonable need in your case. I don't have all the facts here. But, as many on this list have said before, "Fight Rails and it will fight back."
I don't find this unique to Rails. I see this with just about any object-relational mapping systems. It's usually best to have a simple identifier that can be managed entirely by the framework whenever possible. Rows in a database become object instances. Having that one- to-one, object-to-row identity just makes things run much smoother.
All that aside, looking at your programmes table it sure looks to me like a perfectly resaonable join between courses and programes. Why, do you need a composite_primary_keys plugin for this anyway? Why not just let Rails handle that relationship for you using a has_many?
Course has_many :programmes has_many :somethings :through => :programmes <-- ??? wait a second, is this many-to-many or one-to-many?
--- one-to-many --- Course has_many :programmes
Programme has_one :course
--- migration --- class CreateProgrammes < ActiveRecord::Migration def self.up create_table :programmes do |t| t.column :programme_code, :string, :null => false << --- Not the table's PK but a unique programme code column t.column :course_id, :integer t.column :type, :string t.column :last_updated, :timestamp, :null => false end
add_index :programmes, :programme_code, :unique => true end
def self.down drop_table :programmes end end
Note: This table will have an id column since you didn't tell Rails not to create one.
--- Before Save --- Then write a before_save method to generate a user presentable programme_code for display in your interface.
Again, I'm speculating a lot here. I just wanted to make sure you're thinking about this the right way.