Route parameters in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are route parameters in Rails?

Route parameters are dynamic parts of a URL that Rails captures and passes to controller actions as variables. They let you handle URLs with changing values, like user IDs.

beginner

How do you define a route with a parameter in Rails?

You add a colon before a name in the route path, like get '/users/:id', to: 'users#show'. The :id is the route parameter.

beginner

How do you access route parameters inside a Rails controller?

You use the params hash. For example, params[:id] gives you the value of the :id parameter from the URL.

intermediate

What happens if a route parameter is missing in the URL?

If the route expects a parameter but it is missing, Rails will not match that route and usually returns a 404 error because the URL does not fit the route pattern.

intermediate

Can route parameters be used for multiple values in Rails?

Yes, you can define multiple parameters like /posts/:post_id/comments/:id. Each parameter is accessible via params[:post_id] and params[:id].

In Rails, how do you define a route that accepts a user ID as a parameter?

A get '/users/*id', to: 'users#show'

B get '/users/:id', to: 'users#show'

C get '/users', to: 'users#show'

D get '/users/id', to: 'users#show'

The colon before 'id' defines a route parameter named 'id'.

How do you access the route parameter 'id' inside a Rails controller?

A params.id

B request.id

C params[:id]

D session[:id]

Route parameters are accessed via the params hash using symbols, like params[:id].

What will happen if you visit '/users/' but the route expects '/users/:id'?

A Rails will redirect to '/users/1'

B Rails will match the route and set id to nil

C Rails will show the users list

D Rails will return a 404 error

The route requires an :id parameter, so missing it causes no match and a 404 error.

Can you have multiple route parameters in a single Rails route?

A Yes, like '/posts/:post_id/comments/:id'

B No, only one parameter is allowed

C Yes, but only if they are separated by commas

D No, you must use query strings for multiple values

Rails supports multiple parameters in routes by adding multiple colon-prefixed names.

Which of these is NOT a valid route parameter name in Rails?

A :123param

B :user_id

C :id

D :post_id

Parameter names must start with a letter or underscore, not a number.

Explain how route parameters work in Rails and how you use them in a controller.

Think about how URLs can change and how Rails captures those changes.

Describe what happens when a route parameter is missing in a URL that expects it.

Consider how Rails matches URLs to routes.