Check if an ActiveRecord model can be destroyed, and in what order the association should be deleted

active_record_dependancy_graph.rb

Rails.application.eager_load!

class ActiveRecordDependancyGraph
  include TSort
  attr_reader :graph
  def initialize root_model
    @graph = {}
    @model = root_model

    fetch_children @model
  end

  def fetch_children model
    return if model.nil?
    return if graph[model.name]

    child_models = model.reflect_on_all_associations(:has_many).collect do |ar| 
      ar.klass
    rescue NameError => e
    end

    graph[model.name] = child_models.compact.collect &:name

    child_models.each do |child|
      fetch_children child
    end
  end

  def tsort_each_child(model_name, &block)
    graph[model_name].each(&block)
  end

  def tsort_each_node(&block)
    graph.each_key(&block)
  end
end

example.rb

ActiveRecordDependancyGraph.new(Site).tsort
#=> TSort::Cyclic: topological sort failed: ["MailerPreference", "Course", "DripSequence", "Student", "MembershipSubscription", "MembershipPost", "MembershipPlan", "Visitor", "CourseCategory"]
ActiveRecordDependancyGraph.new(Section).tsort
#=> ["Video", "Download", "SectionRestriction", "StudentContentBlock", "Like", "Comment", "ContentBlock", "Section"]