```ruby
class AddPrivateProfileToUsers < ActiveRecord::Migration
  def change
    add_column :users, :private_profile, :boolean, index: { where: "(private_profile = true)" }, default: false
  end
end
```

Make private_profile flag true by default.
user
```ruby
class AddPrivateProfileToUsers < ActiveRecord::Migration
  def change
    add_column :users, :private_profile, :boolean, index: { where: "(private_profile = false)" }, default: true
  end
end
```
assistant