Question

I have a Products table and want to add a column:

t.references :imageable, :polymorphic => true

I was trying to generate migration for this by doing:

$ rails generate migration AddImageableToProducts imageable:references:polymorphic

but I am obviously doing it wrong. Can anybody make any suggestion? Thanks

When I try to manually put it in after generating the migration, I did it like this:

class AddImageableToProducts < ActiveRecord::Migration
  def self.up
    add_column :products, :imageable, :references, :polymorphic => true
  end

  def self.down
    remove_column :products, :imageable
  end
end

and it still hasn’t worked

Answer 1

Before Rails 4 there was no built-in generator for polymorphic associations. If you are using an early version of Rails generate a blank migration and then modify it by hand according to your needs.

Update:
You’ll need to specify which table you’re changing. According to this SO answer:

class AddImageableToProducts < ActiveRecord::Migration
  def up
    change_table :products do |t|
      t.references :imageable, polymorphic: true
    end
  end

  def down
    change_table :products do |t|
      t.remove_references :imageable, polymorphic: true
    end
  end
end

Rails 4 added a generator for polymorphic associations (see simon-olivier answer)