1class AddUniqueConstraintToUserId < ActiveRecord::Migration
 2  def up
 3    remove_index :profiles, :user_id
 4    add_index :profiles, :user_id, unique: true
 5  end
 6
 7  def down
 8    remove_index :profiles, :user_id
 9    add_index :profiles, :user_id
10  end
11end