class MyFeedsMigration < ActiveRecord::Migration
  def change
    create_table :feeds do |t|
      #necessarily
      t.references :source, :polymorphic => true, :null => false
      t.string :source_identify, null: false
      t.string :event, null: false

      #not necessarily, but maybe you need
      #you can also customize your columns
      t.references :target, :polymorphic => true

      t.timestamps
    end

    add_index :feeds, :source_identify
  end
end