A registry allows you to separate your resources from your api module, to reduce improve compile times and reduce compile time dependencies.

For example:

defmodule MyApp.MyRegistry do
  use Ash.Registry,
    extensions: [Ash.Registry.ResourceValidations]
    # This extension adds some simple validations, for example that
    # all related resources are also present in this registry.

  entries do
    entry MyApp.Resource
    entry MyApp.OtherResource
  end
end