Question

Is it possible to create an attribute for a class that is an array? I tried reading this but I didn’t get much out of it. I want to do something like this:

class CreateArches < ActiveRecord::Migration
  def change
    create_table :arches do |t|
      t.string :name
      t.array :thearray
      t.timestamps
    end
  end
end

such that when I call .thearray on an instance of Arch I get an array that I can add new elements to.

ruby-1.9.2-p290 :006 > arc = Arch.new
ruby-1.9.2-p290 :007 > arc.thearray
 => [] 

Answer 1

While you can use a serialized array as tokland suggested, this is rarely a good idea in a relational database. You have three superior alternatives:

• If the array holds entity objects, it’s probably better modeled as a has_many relationship.
• If the array is really just an array of values such as numbers, then you might want to put each value in a separate field and use composed_of.
• If you’re going to be using a lot of array values that aren’t has_manys, you might want to investigate a DB that actually supports array fields. PostgreSQL does this (and array fields are supported in Rails 4 migrations), but you might want to use either a non-SQL database like MongoDB or object persistence such as MagLev is supposed to provide.

If you can describe your use case — that is, what data you’ve got in the array — we can try to help figure out what the best course of action is.