[Rails] ActiveAdmin - belongs

To nest the resource within another, you can use the belongs_to method

ActiveAdmin.register Project
ActiveAdmin.register Ticket do
  belongs_to :project
end

You can also use sidebar

ActiveAdmin.register Project do

  sidebar "Project Details", only: [:show, :edit] do
    ul do
      li link_to "Tickets",    admin_project_tickets_path(resource)
      li link_to "Milestones", admin_project_milestones_path(resource)
    end
  end
end

ActiveAdmin.register Ticket do
  belongs_to :project
end

ActiveAdmin.register Milestone do
  belongs_to :project
end

Source

https://activeadmin.info/2-resource-customization.html

[Rails] ActiveAdmin - belongs_to

Source