Create a Form With Two Actions on Activeadmin

In a project that already using Activeadmin I had the requeriment of modify the actual form to create a student, but without validating that, so the solution was create into the model of active admin form and declare the form with two actions, one with the clasical behaviour and other when passed the params[:managed] with a custom route

ActiveAdmin.register InvestmentItem do
  # ..
  form do |f|
    f.inputs do
      f.input :student, as: :select, collection: User.students
      f.input :amount
      unless params[:managed]
        f.input :course, as: :select, collection: Course.all
        f.input :created_at
      end
    end
    if params[:managed]
      f.action :submit, as: :input, button_html: { formaction: :managed_create }
    else
      f.actions # this go to create/update
    end
  end

  # ...

  controller do
    def managed_create
      # do whatewer you want
    end
  end
end

Then button_html: { formaction: :managed_create } options in a :submit, does the trick.