reversible migration

db/migrate/20230722054450_turn_invoice_amount_to_float.rb

 class TurnInvoiceAmountToFloat < ActiveRecord::Migration[7.0]
-  def change
+  def up
     add_column :universities, :contribution_amount, :float
     University.find_each do |university|
       university.update_column :contribution_amount, university.invoice_amount.to_f
     end
     remove_column :universities, :invoice_amount
   end
+
+  def down
+    remove_column :universities, :contribution_amount, :float
+    add_column :universities, :invoice_amount, :string
+  end
 end