How do you stream from a database table using ActionController::Live?

Question

Setup: In my environment, a Java program writes to a PostgreSQL database table called readings continuously, say every second.

I am building a rails app that connects to the same database and displays those readings. Here is a picture of the readings being displayed statically.

Problem: To see new readings, I have to refresh.

Question: How can I use ActionController::Live to make this page show new records? I imagine that I need to poll the database for new records and update the @readings variable but I do not know how.

Here is the beginning of readings_controller.rb.

class ReadingsController < ApplicationController                                    
  include ActionController::Live                                                    

  before_action :set_reading, only: [:show, :edit, :update, :destroy]               

  # GET /readings                                                                   
  # GET /readings.json                                                              
  def index                                                                         
    @search = Reading.search(params[:q])                                            
    @readings = @search.result.order('time DESC').paginate(:page => params[:page])
  end 

Answer 1

ActionController::Live is a beast of its own

You can't use it like a normal controller / action - it has to work with SSE's or web sockets to provide connectivity. I don't believe you can get it working without having a perpetual connection

Excellent resource

---

ActionController::Live

The way I see this working is:

• You connect via controller / action
• Connection is maintained (with web socket / SSE on front-end)
• Any updates are published to connection (via ActionController::Live)

I would do this:

---

JS

Create an SSE listener:

#app/assets/javascripts/special_javascript.js
jQuery(document).ready(function() {
  setTimeout(function() {
    var source = new EventSource('/your/action');
    source.addEventListener('refresh', function(e) {
      window.location.reload();
    });
  }, 1);
});

---

Controller

class ReadingsController < ActionController::Base
  include ActionController::Live

  def create
    response.stream.write "Updated" #-> send updated db stuff
    response.stream.close
  end
end

This will allow you to monitor for changes in the DB. If you're looking to update the page with the new DB information, we'll have to look into how you pass the data through

There's actually a service we highly recommend called Pusher to handle this for you