Rails Basic Skills: Exception Handling

Stop the server. Now we want to edit customers_controller.rb again. Take out the byebug line. Add this line near the top of the file, right after the “class” line, but before the “before_action” line:

rescue_from ActiveRecord::RecordNotFound, with: :catch_not_found

And, add this method to the bottom of the file, right before the end that ends the class:

def catch_not_found(e)
      Rails.logger.debug("We had a not found exception.")
      flash.alert = e.to_s
      redirect_to customers_path
end

Explaining This Code

The rescue_from statement says that if an exception of the specified type occurs, call the catch_not_found method.

The Rails.logger.debug statement writes an entry to the Rails log. You will see it in the console, and it is also written to the log/development.log file.

The flash.alert statement takes the message from the exception and stores it in the flash object so that it can be displayed to the user.

The redirect_to statement puts up the index page again, so that the user does not see that other error page.

Trying the Code Again

Now save the controller file, restart the server, and go to the /customers/567 URL again. You will see that the index page is shown, instead of the error. You will see that the “we had a not found exception” line is in the server log when you look at the console. BUT the user does not see the error message. We need to do more to make that work.

Modifying the Layout

Edit the app/views/layouts/application.html.erb file. Add these lines, just below the <body> tag:

<% if flash[:alert].present? %>
    <p class="my_alert"><%= flash[:alert] %></p>
<% end %>

CSS Files for Rails are in the app/assets/stylesheets Folder

Open app/assets/stylesheets/application.bootstrap.scss . (Your starter repository was configured with bootstrap. The R7-blog repository was not configured with bootstrap, so it has application.css instead of the bootstrap version.) Add this CSS style rule at the bottom:

.my_alert {
  color: red;
}

This corresponds to the my_alert class that was used in the customer_layout.html.erb file. We want alerts to show in red. (You can try adding other styling if you want this application to look cool, but let’s make this work first.)

Now Try /customers/567 Again

You will see that you are once again directed to the index page, but at the top, in red, there will be an error message:

Couldn’t find Customer with ‘id’=567

This is a much more user friendly message than before.