Rails API--- Update Course with topics and Topics with subtopics

Question

I need help need to create topics with nested array subtopics and under one API endpoint. I would like where i can update topics under a course by submitting course_id, if the topic is not present i created new topic and if topic_id is present i can update the topic or and i supply empty array i delete all topic_ids and the same goes for subtopic. The challenge is that i have managed the topics and now i need subtopics under one endpoint for Rails api to update and create and delete.

sample of array i want to update under topics which are under a course

    [
        {
            "topic_id" : 636015,
            "name": "Topic 1",
            "body": " Great Lord"
            "sub_topics" : [
                {
                    "title": "Sub Topic 1",
                    "url_path": "https:/dasdasdasdas"
                }
            ]
        }
    ]





Endpoint -----

  def save_changes
                            require 'json'
                            @course = Course.find(@course_id)
                            if @course.present?
                             @update= update_course
                             else 
                            end 
                            if params[:topics].present?
                               @x= JSON.parse(params[:topics]).each do |topic|
                                    if topic.key?('id')
                                     @topic= @course.topics.find(topic['id'])
                                     @topic_id= @topic.id
                                     p @topic_id, " this topic ID exists"
                                     @topic.update(topic)
                                   else
                                  @course.topics.create!(topic)
                                end
                               end
                              end 
                                  if JSON.parse(params[:topics])==[]
                                   @course= Course.find(@course_id)
                                   @delete= @course.topics.where(course_id: @course.id)
                                   @delete.each do |topic|
                                   topic.destroy
                                  end
                              end 
                              if params[:subtopics].present?
                               @x= JSON.parse(params[:subtopics]).each do |subtopic|
                                   @topic= Topic.find(@topic_id)
                                    if subtopic.key?('id')
                                     @subtopic= @topic.subtopics.find(subtopic['id'])
                                     puts @subtopic.title
                                     @subtopic_id= @subtopic.id
                                     p @topic_id, " this sub topic ID exists"
                                     @subtopic.update(subtopic)
                                   else
                                  @topic.subtopics.create!(subtopic)
                                end
                               end
                              end 
                              if JSON.parse(params[:subtopics])==[]
                                   @delete= @topic.subtopics.where(topic_id: @topic.id)
                                   @delete.each do |subtopic|
                              subtopic.destroy
                                  end
                            end 
                          end