app/services/add_comment_to_post.rb

class AddCommentToPost
  def initialize(post:, comment:)
    @post = post
    @comment = comment
  end

  def call
    @post.comments.create(@comment)
    @post
  end
end


app/services/remove_comment_from_class.rb

class RemoveCommentFromPost
  def initialize(post:, comment:)
    @post = post
    @comment = comment
  end

  def call
    @post.comments.@comment.id.destroy
    @post
  end
end

def create
        #this one works:
        #@post.comments.create! comment_params

        AddCommentToPost.new(@post, @comment).call
        redirect_to @post


     def destroy
         RemoveCommentFromPost.new(@post,@comment).call
         redirect_to @post

Rails.application.routes.draw do

  resources :posts do
    resources :comments
  end

  root "posts#index"

end