Action methods in Ruby on Rails - Step-by-Step Execution

Concept Flow - Action methods

HTTP Request Received

↓

Router Matches URL

↓

Controller Selected

↓

Action Method Called

↓

Action Executes Code

↓

Render View or Redirect

↓

HTTP Response Sent

When a web request comes in, Rails finds the right controller and calls the action method, which runs code and sends back a response.

Execution Sample

Ruby on Rails

class BooksController < ApplicationController
  def show
    @book = Book.find(params[:id])
  end
end

This action method finds a book by its ID and prepares it for the view to display.

Execution Table

Step	Action	Code Executed	State Change	Output/Next Step
1	Receive HTTP GET /books/3	Router matches to BooksController#show	Controller set to BooksController	Call show action method
2	Call show method	@book = Book.find(params[:id])	@book set to Book with id=3	Prepare data for view
3	Render view	Render show.html.erb with @book	View ready with @book data	Send HTTP response with HTML
4	Response sent	HTTP 200 OK with book details	Request complete	End

💡 Action method finishes after rendering view or redirecting, response sent to client

Variable Tracker

Variable	Start	After Step 2	Final
@book	nil	Book(id=3, title='Example')	Book(id=3, title='Example')

Key Moments - 2 Insights

Why does the action method need to set instance variables like @book?

Instance variables like @book are used to pass data from the action method to the view template, as shown in step 2 and 3 of the execution_table.

What happens if the action method does not render or redirect?

Rails will try to render the default view matching the action name automatically after the action method finishes, as seen in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of @book after step 2?

A Book with id=3

B nil

C params[:id]

D Empty object

💡 Hint

Check the 'State Change' column in step 2 of the execution_table

At which step does Rails send the HTTP response back to the client?

A Step 1

B Step 4

C Step 2

D Step 3

💡 Hint

Look at the 'Output/Next Step' column for when the response is sent

If the action method did not set @book, what would happen in the view rendering step?

A View renders with empty @book

B Rails skips rendering the view

C View raises an error for missing @book

D Rails redirects automatically

💡 Hint

Instance variables must be set in the action method to be used in the view (see variable_tracker)

Concept Snapshot

Action methods are controller functions called by Rails when a matching URL is requested.
They run code to prepare data, usually setting instance variables.
After running, Rails renders a view or redirects.
Instance variables connect controller data to views.
If no render or redirect, Rails renders default view automatically.

Full Transcript

In Rails, when a web request comes in, the router finds the right controller and action method. The action method runs code, often setting instance variables like @book to pass data to the view. After the action runs, Rails renders the matching view template or redirects. The HTTP response is then sent back to the client. This flow ensures the right data is shown on the page. If the action method does not explicitly render or redirect, Rails automatically renders the default view for that action. Instance variables are key to sharing data between the controller and the view.