Rails noob question about scope (params in controller)

I’m testing RubyMine and while debugging a controller (class PostsController < ApplicationController in method #show) I see that I can access:

  • self
  • global variables
  • params

I try to understand the inner workings of ruby and rails and I don’t understand where params comes from and why I can access it. Any advice for me? Maybe also how I can dynamically investigate these cases while debugging. Thanks!

Certainly! Let’s break this down.

Ruby on Rails Architecture

First, understanding the architecture of Ruby on Rails helps. Rails is a Model-View-Controller (MVC) framework. In this architecture:

Model: Represents the data and the business logic.

View: Represents the user interface and display.

Controller: Acts as an intermediary between the Model and the View, receiving requests, processing data, and returning responses.

Where params Comes From

In Rails, when a request is made to a controller action, the framework creates a params hash with all the parameters from the request. This includes:

Parameters from the query string

Parameters from the request body (like form data)

Route parameters (like the id in posts/:id)

The params method is available in all controllers and views. It’s defined in ActionController::Base, from which ApplicationController (and subsequently your PostsController) inherits. So, when you’re inside any controller action, you can access the params hash to get information about the request.

Investigating with Debugging

RubyMine provides a robust debugging environment. Here’s how you can investigate further while debugging:

Breakpoints: Set a breakpoint in your controller action (or any Ruby code). When the execution reaches that point, it’ll pause, and you can inspect the current state.

Inspecting self: When paused at a breakpoint, evaluate self. In a controller action, self refers to the instance of the controller. Through it, you can access instance variables, methods, and more.

Investigate Inherited Methods: While paused, you can see a list of methods available on self. This can help you understand what methods are defined by Rails and available in your controller. Look specifically for methods inherited from ActionController::Base or its ancestors.

Rails Source Code: Sometimes, to really understand, you may want to dive into the Rails source code. It’s open-source, and you can find it on GitHub. For example, if you’re curious about how params is implemented, you could look at the source code for ActionController::Base.

Rails Console (rails c): This is an IRB session with your Rails environment loaded. You can experiment and run any Ruby or Rails code here. It’s a great way to test out things without affecting your running application.

Logs: Check the Rails server logs. They provide detailed information about each request, including parameters.

Documentation & Community: The Rails guides and API documentation are comprehensive. Plus, there’s a massive community around Rails, so there are plenty of resources, forums, and discussions available to help.

In your specific case, when you’re paused at a breakpoint in RubyMine inside your #show action, try evaluating self.class.ancestors. This will show you all the classes/modules your controller inherits from. This can give you insight into where certain methods (like params) come from.

Remember, Rails does a lot of things “magically” behind the scenes using metaprogramming, conventions, and inheritance. As you dig deeper, you’ll get more familiar with its inner workings.

this is what comes back asking the AI, others might have better and detailed answers, however if you have access to chatgpt 3.5 or 4 its really nice to build something with them together. I am just in the process of doing that and stretching it out by questioning and wanting changes to what chatgpt suggest, trying it out etc because I learn from the mistakes the AI sometimes makes. :slight_smile:


I think you’ve just catapulted a dinosaur (I’ve worked on the linux kernel 10+ years ago before taking a long break from coding) into a new age of programming…

This is amazing, thanks!

1 Like

great but is it correct? that thing lies sometimes or gets things wrong. and also I have restarted that project I am doing with the alien 8 times now. Its getting there but since I am a noob and use scaffolds I had to go back to get the tables I need right. and on every restart it suggest slightly different ways to do it, very entertaining sometimes. :slight_smile: have a lovely day.

Let’s say it was correct enough :stuck_out_tongue:

I thought params is an object, but GPT corrected this assumption to a method. Also the inheritance chain was close enough. I checked it, and params is defined in ActionController::StrongParameters and not ActionController::Base. Maybe in an older version it was in ActionController::Base? But it’s correct that my PostController inherits the method.

My current working assumption is that RubyMine is set up in a way that it automatically calls and shows the return value of params when breaking into controller code as rails developers need it all the time.

:baseball: he best way to understand what is happeningn to read the guide: Action Controller Overview — Ruby on Rails Guides or the docs for ActionController::Base ActionController::Base

Controllers are weird, especially if you are coming to Rails from any other OO language, because you don’t instantiate them, don’t call their methods, their methods don’t get arguments, and the return values are ignore.

Inspecting the class via params.class was a good way to start figuring out the specifics, and you should use api.rubyonrails.org to see any additional docs on the classes you discover this way.

The AI’s answer is wrong on some specifics that will confuse you later:

  • params is not defined on ActionController::Base, but on a super class
  • params is not a hash but, as you discovered, an instance of StrongParameters
  • Examining the methods available on self is going to produce a lot of private methods you should not rely on or call - only call methods that are documented
  • The logs do not show you parameters on POST, PUT, or PATCH requests by default

Best bet is to start with the Guide and API docs. For Rails they are very well maintained.


I’ve been working on a Rails application, and I’ve run into a problem with my custom routes. I’ve defined a custom route for a special page in my config/routes.rb file, but when I try to access it, I keep getting a “No route matches” error. I’ve double-checked my route definition, and it looks fine to me. Any ideas on what could be causing this issue or how to fix it?

I’m working on a controller, specifically the show method in the PostsController , I noticed that I could access the params hash, self , and even global variables during the debugging session. While this capability is helpful for troubleshooting, I find myself seeking a deeper understanding of the inner workings of Ruby and Rails to comprehend why I can effortlessly access params and how it gets populated with request data.