Rspec SystemStackError堆栈级别太深

Question

I'm developing an API using Ruby on Rails. I've created some specs for posts_controller.rb and I'm having this error while running the specs

SystemStackError: stack level too deep
./app/controllers/api/v1/posts_controller.rb:10:in `show'
./spec/controllers/api/v1/posts_controller_spec.rb:8:in `block (3 levels) in <top (required)>'

This is my posts_controller_spec.rb

require 'spec_helper'

describe API::V1::PostsController do
  describe "GET #show" do
    before(:each) do
      @post = FactoryGirl.create :post
      get :show, id: @post.id
    end

    it "returns the information about a post on a hash" do
      post_response = json_response[:post]
      expect(post_response[:description]).to eql @post.description
    end

    it "has the user as a embeded object" do
      post_response = json_response[:post]
      expect(post_response[:user][:email]).to eql @post.user.email
    end

    it { expect(response.status).to eql 200 }
  end
  .
  .
  .

This is my posts_controller.rb

class API::V1::PostsController < ApplicationController
  respond_to :json

  def show
    respond_with Post.find(params[:id])
  end

  .
  .
  .

Anybody have ideas to solve this problem ?

I realized that this is the line that causes the error, anyone know why? In post_serializer.rb file I have this

class PostSerializer < ActiveModel::Serializer
  attributes :id, :description, :price, :published
  has_one :user # this is the line !!!
end 

If I remove this line the problem will be fixed, but anyone knows why ?

Answer 1

You have a circular reference in your serialiser: the post tries to serialise its user, but the user serializer serializes the users posts, which then serialise the user etc.

There is a lengthy github issue about this issue in active_model_serializers 0.9.x. The issue is apparently fixed in 0.10, although that doesn't appear to be compatible with rails 3.x

A common technique appears to be to have 2 versions of the user serializer: one which includes posts and one which does not.