how to namespace in rails engine

Question

I trying create a rails engine

Content default

lib/abc_xyz.rb

require 'abc_xyz/engine'

module AbcXyz
end

abc_xyz/engine.rb

module AbcXyz
  class Engine < ::Rails::Engine
    isolate_namespace AbcXyz
  end
end

But, i want nested it in a namespace, as below:

lib/abc_xyz.rb

require 'abc/xyz/engine'

module Abc
  module Xyz
  end
end

abc/xyz/engine.rb

module Abc
  module Xyz
    class Engine < ::Rails::Engine
      isolate_namespace Abc
    end
  end
end

but, rake abc:install:migrations not working for me . How to do it?