tab/db/migrate/20170109123717_create_requests.rb

class CreateRequests < ActiveRecord::Migration
  def change
    create_table :requests do |t|
      t.references :debtor,   null: false
      t.references :creditor, null: false
      t.references :issuer,   polymorphic: true, null: false
      t.integer :amount, null: false, default: 0
      t.string :message

      t.integer :status, default: 0

      t.timestamps null: false
    end

    add_index :requests, :debtor_id   unless index_exists?(:requests, :debtor)
    add_index :requests, :creditor_id unless index_exists?(:requests, :creditor)
    add_index :requests, [:issuer_type, :issuer_id] unless index_exists?(:requests, :issuer)

    add_foreign_key :requests, :users, column: :creditor_id
    add_foreign_key :requests, :users, column: :debtor_id
  end
end