Ruby on Rails: Aggregating several columns into an Array

Question

I'm developing a Ruby on Rails app where one of my database tables has 10 columns (pile_1 through to pile_10). It would be convenient to access these columns in the model as a 10-element Array.

It feels like I should be able to coerce composed_of into doing what I want, but I can't figure out how. Can anyone enlighten me, or suggest a better tactic?

Answer 1

Would

def piles
    (1..10).map{ |num| self[ "pile_#{ num }"]}
end

not suffice?

Answer 2

Since you have the power to change the schema, you should. Storing an array as separate columns in a table is denormalized. Whether or not your schema is normalized might not matter to you, but your current difficulty is a direct result of a denormalized schema.

What you ought to do is to create a new table, piles, like so. I'll use postgres syntax, since that's what I know. I don't know the name of the table which currently contains all of the piles* columns, so I'll call it "foo":

create table piles (
  id serial primary key,
  foo_id int not null references foo(id),
  value text not null,
);

Every column you now have in foo exists instead as a row in piles. In the model for piles, add:

belongs_to: foo

and in the model for foo, add:

has_many: piles

In your controller, once you have a foo in hand, you can access its piles with foo.piles