Historical errata for Agile Web Development with Rails 4

tag. As it stands, the css is not being applied as intended to the table rows and the Show/Edit/Destroy links.

Medal!!!

Nick :)
n.bulmer@live.co.uk

In the first line in the list the ‘object’ and ‘blob’ seem to be out of place. Adding cell borders might be a good idea to improve readablity.

11.4 Iteration F4

code has not specific location

Please discuss the creation of a new file and the purpose of the controller/concerns folder. Nothing says outright that “we are going to create a new file in the concern folder for..” and it would be nice to have an explanation.

In the tenth-eleventh line from bottom, there is a space between “command” word and period sign:
“… automatically by the scaffold command . This method…”

This causes the period to stay alone at the beginning of new line.

There is no introduction or explanation as to the purpose of controllers/concerns. It appears without hardly any context. What is a concern used for? Why doesn’t the author state that we are making a “concern.” These are VERY important questions that need to be answered since this seems to be a new feature in Rails 4.

I am reading a book P2.2 from 2012 and studying Rails4. I found a typo in the examples data from media.pragprog.com/titles/rails4/code/rails4-code.zip: there is a file at /rails%20code/rails40/depot_i/test/models/cart_test.rb, it contains a unknown variable book_one on line 27, and tests fail. It should be replaced with ruby_book.
Thanks.

The link to the MiniTest docs at the bottom of the page is broken.

Your code for show.html.erb at the bottom of the page doesn’t fix the DRY issue. I believe it should be:
<% if notice %>

<%= notice %>

<% end %>
<%= render @cart %>

Adding this to application.js no longer works:
//= require jquery-ui

After about 15 minutes of fighting, I found this works:
1. gem install jquery-ui-rails
2. within Gemfile add this:
gem ‘jquery-ui-rails’
3. use this require in the example instead:
//= require jquery.ui.all

The paragraph under current_card.rb states, that the code finally returns the new cart. As I see it, it doesn’t, but returns the cart’s id!

The route mapping delete ‘logout’ => :destroy does not work.

“In effect, though, you can ignore that it’s a hash and pretend that Ruby has keyword arguments.”

It sounds like this should have been updated for Ruby 2.0

The following sentence contains a query string within the URL, meaning a GET request is performed. However, the sentence indicates that a POST request is performed:

“The routing component receives the incoming request and immediately picks it apart. The request contains a path (​/line_items?product_id=2​) and a method (this button does a POST operation; other common methods are GET, PUT, PATCH, and DELETE).”

Thanks,

Matt

assert_select ‘tr#current_item td’, /Programming Ruby 1.9/
The dot in the RegEx should be escaped.

Mention of impossibility of instantiating modules. But subsequent statement says “module’s instance method”.

(FYI the problems here could be due to changes in jQuery UI implementation)

The inclusion of:

form, div {
display: inline;
}

inside the scope of #side seems to be necessary since there is nothing to put side-by-side. Furthermore, this makes div#cart display: inline, which break the jquery-ui blind animation because div#cart has no natural height, which jQuery requires to complete the blind animation.

Removing this CSS rule fixes the animation. However, there is still a small issue where there is a hitch at the end of the animation due to two things:

1) CSS margin collapse of the h2 at the top of the cart causes jQuery to miscalculate the height of div#cart (very obvious in the web inspector)

2) jQuery determines the height of div#cart before the newly added line item is added to the table

These two elements cause jQuery to underestimate the height of div#cart, leading to a hitch at the end of the animation as the animation wrapper div is removed and div#cart jumps back to its natural height. 1) can be fixed by removing margin-top from the h2. 2) can be fixed by moving the show() call to after the cart HTML is replaced in create.js.erb.

Pg 169 includes the 2nd of two adjustments to orders_controller_test.rb in chapter (12 “Check Out”). However, the chapter has no steps for running “rake test”.

(Perhaps reader is expected to run “rake test” by habit by now. If so, this could usefully be noted at some point.)

Thanks!

Book say to change this flag to true to enable caching:

config.action_controller.perform_caching = true

But it doesn’t work without this flag also being set to true:

config.cache_classes = true

To get the file products/index.html.erg to render properly in Firefox I had to add ‘class=“product”’ (no single quotes) to the opening table tag, and remove all the comments from the stylesheet file products.css.scss. I am developing on Windows 7.

Between pages 129 and 130, essentially in the middle of a paragraph, while we are still talking about making a smarter cart, the sample codebase switches from being in depot_h, to being in depot_i. This is really confusing to someone who has screwed up their codebase and just wants to revert to some particular state that works.

It would be really helpful in general if the depot_#{letter} would line up with the chapter/section that is currently in progress. So, for example, section 10.3, also known as “E3” is called “Finishing the Cart”, but the associated codebases come from depot_h and depot_i. It would be much clearer if all of the codebase in “Finishing the cart” came from a directory called “depot_e3”

Thanks.

“Carrito bonita” -> “Carrito bonito”
because
carrito nombre masculino

$(document).on “ready page:change”, ->
\t$(‘.store .entry > img’).click ->
\t\t$(this).parent().find(‘:submit’).click()

produces that products will be added twice (Mac OS X 10.9 Safari 7.0.1/Chrome 31.0)

fix: $(document).on “ready, page:change”, ->

The changes made to the default ‘_form.html.erb’ file (to improve the appearance of the user creation/modification form) created by the Rails scaffolding have not been indicated with the small grey arrows on the left hand side of the code, as they are in other examples.

Should the route “delete ‘logout’ => :destroy” perhaps instead be “get ‘logout’ => :destroy” to permit logging out via a standard link in a browser?

Hello People,

Thanks for the fantastic reference. Maybe its just my lack of understanding here, but the following code (from the book) seems to work, but I don’t understand the magic.

1. rails40/depot_g/app/models/cart.rb
   def add_product(product_id)
   current_item = line_items.find_by(product_id: product_id)
   if current_item
   current_item.quantity += 1
   else
   current_item = line_items.build(product_id: product_id)
   end
   current_item
   end

From playing with the code it isn’t obvious to me why I don’t need to write something more like:
…
current_item = line_items.find_by(product_id: product_id, cart_id: self.id)
…
current_item = line_items.build(product_id: product_id, cart_id: self.id)
…

I’m just wondering if there is some magic that helps a Cart get the LineItem that indeed corresponds to the particular Cart in question. If I don’t need to pass the cart id as I do in the two changed lines above, I think it might be good to explain why in this section.

Or is it maybe a bug?

Cheers :-)

Where it says “Keys in a particular hash must be unique—you can’t have two entries for :drum.”, should say “Keys in a particular hash are unique—the last of multiple entries for :drum will cancel any preceding entries.”

Try the follwing in the console:
Product.create(name: ‘First name entry’, name: ‘Second name entry’)

“Why test against 1 cent, rather than zero? Well, it’s possible to enter a number such as 0.001 into this field. Because the database stores just two digits after the decimal point…”
When we set the validation to greater_than: 0, values like 0.001 do get stored in the database, in spite of the schema explicitly saying “precision: 8, scale: 2”…
Not sure where the error is, but could it be in your explanation?

Even after applying the changes, notably to the destroy method in the carts controller, I’m still capable of browsing to which ever cart I like, at carts/show/cart_id, click the empty button, and the cart is destroyed. So I’m able to delete someone else’s cart…

I’ve added to /test/controllers/carts_controllers_test.rb :

test “shold not destroy someone else’s cart” do
session[:cart_id] = nil
assert_difference(‘Cart.count’, 0) do
delete :destroy, id: @cart
end
end

And the result:

Failure:
CartsControllerTest#test_shold_not_destroy_someone_else’s_cart [/home/oz/rails/depot/test/controllers/carts_controller_test.rb:51]:
“Cart.count” didn’t change by 0.
Expected: 2
Actual: 1

In introducing methods, you make use of a return statement that is in practice unwarranted since Ruby methods return their last-evaluated expression. To say the following would suffice to return the expected result:

`def say_goodnight(name)
result = ‘Good night, ’ + name
end`

I think that, regarding the numerical validation of the price, it must be stressed that errors could also be produced by storing legal but unintended data as a result of type casting, conversions and maybe bugs performed before reaching the database.

If I use 0.0099999999999999999999 as price for the product, it passes validation, because somewhere between the interface and the database this number gets rounded to 0.01. I can’t think of a better example now, but I think you got the idea.

In the second paragraph, it says: “With that change in place, click any Add to Cart button, and you’ll see that the changed item in the cart glows a light green before fading back to merge with the background.”

The problem is that I don’t see any animation. I know the Jquery code is doing something, because running it from the Chrome console (first the css instruction, then the animate instruction) changes the background color to highlighted, and then back, but the change is immediate, not gradual. I tried the workarounds given by other users but I couldn’t make it work and I don’t want to pass a lot of time on it. I expect a comment from the authors, thanks.

In the cited code for the _cart partial, the line

should be

Your Cart

and that’s all!

The code to put in create.js.erb seems wrong in two aspects: first, the line we add should be added between the two existing lines, otherwise it will make the test before changes are done to the DOM. Second, the test must be comparing to 2, not 1, since the least number of tr’s is 2 (we must count the total line).

Another comment: in JavaScript, equality comparison should be done with =. This is surely a typo due to the fact that Ruby uses .

The animation done with Jquery’s ‘show’ just doesn’t work. The cart is shown, but the changes are not animated. I also had the same problem with color highlighting in the previous iteration.

The correct way of accessing `product_id` from request’s params is: params[:line_item][:product_id], not params[:product_id]

In the paragraph after the form code, there’s this phrase, which describes the parameters of the *_field_tag helpers: “The first is the name to give to the field, and the second is the value with which to populate the field.”

I think the phrase should be more precise in the sense that the second argument is also used to transport the value between controller and view. It is not just a value, but it’s more like a variable. I tried to write the precise phrase but I failed and I leave that to the authors.

Hyperlink for downloading index.html.erb points to incorrect content.

Seems there is a sentence or two missing from this content in the colored box: “A GET request is defined by HTTP to be used to retrieve
data; it isn’t supposed to have any side effects. Using this parameter in this way
indicates that an HTTP DELETE method should be used for this hyperlink.” The clue is “this parameter” has no clear referent.

“Substitute your host’s name and your application’s directory path in the fol- lowing ServerName line”

should be

“Substitute your host’s name and your application’s directory path in the fol- lowing VirtualHost definition:”

Link on the top of the fixtures has changed in recent rails version (4.1.1) from Fixtures.html to FixtureSet.html

So:
api.rubyonrails.org/classes/ActiveRecord/Fixtures.html

should be:

api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html

legend for Figure 16 Template not found

should not be that as the template index.html.erb, is created when using the rails scaffold controller generator with the index method: rails g controller Store index

Iteration F5, rails40/depot_n/app/assets/javascripts/store.js.coffee
Rails 4.0.5, Turbolinks 2.2.2

The handler registered by $(document).on “ready page:change” fires twice when loading the site in the browser with a Refresh. This causes two click handlers to be registered for each “img” tag. In the end, this means that when an image is clicked, two copies of the same item are added to the cart.

Under the “Subsetting the Records Returned” heading, the text first alludes to the “all()” method but then refers to the “to_a()” method. I am unsure if this is a typo or I am just misreading the text. If the case of the latter, I’m sure there can be some added clarity. Thank you.

in the scaffold code generated by rails (4.1) the following:

<% @order.errors.full_messages.each do |msg| %>

<% end %>

should be:

<% @order.errors.full_messages.each do |message| %>

<% end %>

Should the line:

order = orders[0]

be better placed in the following section of code since it is logically related to the following assertions?

ie.

order = orders[0]
assert_equal “Dave Thomas”, order name

Wouldn’t it be better if there is a note that emphasises that in testing the create method in the user controller the user name (ie ‘sam’) should be different from what we have in the fixtures.yml :one record (ie ‘dave’)

Not to sure what to do with the code on the top of the page, not clear instructions.

$ rails g migration add_image_to_pins image:string

Do you mean?

$ rails g migration add_image_to_pins image_cache:string

4 These uploadersare reusable and the same one can be mounted on multiple models
in our pinmodel:
app/uploaders/image_uploader.rb (WRONG, THIS IS NOT A MODEL)

do you mean?

config/environments/development.rb
only after setting both of the following to true did caching work properly
config.cache_classes = true
config.action_controller.perform_caching = true

In Iteration F3:Highlighting Changes the jQuery-UI library has been updated and the syntax for the entry in application.js to include the Blind Effect is now:
//= require jquery-ui/effect-blind
Instead of:
//= require jquery.ui.effect-blind

Source is; rubydoc.info/gems/jquery-ui-rails/frames

depot code jquery-ui effect blind import:

in depot code the
app/assets/javascripts/application.js
lists the import:
" //= require jquery.ui.effect-blind" at line 24

at github.com slash joliss slash jquery-ui-rails you’ll find the correct import:

//= require jquery-ui/effect-blind

The color does not fade back. It is a book typo and a file typo.
File with typo is rails40/depot_m/app/views/line_items/create.js.erb
There is a space at the beginning of line
animate({’background-color’:‘#114411’}, 1000);
Remove the space and color fades as expected.

Text:
“…we modify our controller to call paginate()…”

Code extract:
@orders = Order.order(‘created_at desc’).page(params[:page])

Text states “paginate()” but code extract uses “page()”.

The code within app/views/layouts/application.html.erb fails to display a cart when the cart is initially empty and the first product is added to it.

The page number might not be correct - I’m using iBooks, and the page no. depends on the window size.

The error is in the code for:
“rails40/depot_m/app/assets/javascripts/application.js”:

Is: “*​//= require jquery.ui.effect-blind”
Should be: “*​//= require jquery-ui/effect-blind”

Book text:

class Cart < ActiveRecord::Base
➤ has_many :line_items, dependent: :destroy
end

But if LineItem is a Model, shouldn’t “has_many” be:

➤ has_many :line_item, dependent: :destroy

using the (singular) model name?

I found the answer relating specifically to “has_many” here:

“guides.rubyonrails.org/association_basics.html#the-has-many-association”

Note the highlight there: “The name of the other model is pluralized when declaring a has_many association.”

Suggest a note on this maverick association in your book as it differs from “belongs_to”, “has_one” and is confusing.

Thank you.

Page 107: after running the scaffold to create the Cart, and migrating it…
the code on page 108 for “/app/controllers/concerns/current_cart.rb” does NOT get created automatically. Are we supposed to create a file in this path? If so, why? Or should the code listed on page 108 supposed to be the contents of “/app/controllers/carts_controller.rb”?

Two descriptions of raw() method are given which contradict each other.

Top of the page : the end sentence dot shouls not be on th ebeginning of the second line… probably due to trhe change of font.

store_controller_test.erb section has a typo in this line:

assert_select ‘.store .entry > img’, 3

it doesn’t work unless you remove the “>” - maybe this was an unintentional carryover from the js/coffeescript? It should be (at least what works for me)

assert_select ‘.store .entry img’, 3

The link on pragprog.com for note #2 takes you to tarballs, but the .tgz tarball is actually rails30. The zip file is correct.

Not a huge problem, but some code specifies a space in ‘Good night, ’ but the output is shown as ‘Goodnight…’. Unless there’s something I don’t get about some automatic concatenation, something went wrong here. Text copied below.

def say_goodnight(name)
result = ‘Good night, ’ + name return result
end

1. Time for bed…
   puts say_goodnight(‘Mary-Ellen’) # => ‘Goodnight, Mary-Ellen’ puts say_goodnight(‘John-Boy’) # => ‘Goodnight, John-Boy’

It seems the notation for jquery-ui changed from:
//= require jquery.ui.effect-blind

to

//= require jquery-ui/effect-blind

The older version doesn’t work with the new library (at least in my configuration).

Thanks,

Ronaldo

This error has been reported before - just note that if you use the old syntax, the animation may fail with no error indicated. The line item stays bright green. (page number is bogus - epub does not have any)
In Iteration F3:Highlighting Changes the jQuery-UI library has been updated and the syntax for the entry in application.js to include the Blind Effect is now:
//= require jquery-ui/effect-blind
Instead of:
//= require jquery.ui.effect-blind

In downloadable example code, in code/rails40/depot_n though depot_v contains an incorrect comment syntax that raises a runtime error in /assets/javascript/store.js.coffee:

ExecJS::RuntimeError in Store#index
Showing <…>/code/rails40/depot_o/app/views/layouts/application.html.erb where line #8 raised:

SyntaxError: [stdin]:5:1: unexpected //
…

The code in question is as follows:
# Place all the behaviors and hooks related to the matching controller here.
# All this logic will automatically be available in application.js.
# You can use CoffeeScript in this file: …/coffeescript.org/

//#START_HIGHLIGHT
$(document).on “ready page:change”, ->
$(‘.store .entry > img’).click ->
$(this).parent().find(‘:submit’).click()
//#END_HIGHLIGHT

Removing the “//” before “START_HIGHLIGHT” and “END_HIGHLIGHT” resolves the error.

In Iteration F3 we add “gem ‘jquery-ui-rails’” and then add it to application.js with:

//= require jquery.ui.effect-blind

but that throws this error:

couldn’t find file ‘jquery.ui.effect-blind’

according to the Github page:
joliss/jquery-ui-rails

it should be added like this:

//= require jquery-ui/effect-blind

The changed line should be
require jquery-ui/effect-blind
instead of
require jquery.ui.effect-blind

Refer - stackoverflow.com/questions/24819381/application-js-cant-find-jquery-ui-effect-blind

Apache 2.4 has changed the access configuration:

Remove `Order allow, deny` and `Allow from all` and add `Require all granted`

<VirtualHost *:80>
ServerName depot.yourhost.com
DocumentRoot /home/rubys/deploy/depot/public/

AllowOverride all
Options -MultiViews

1. Order allow,deny
2. Allow from all
   Require all granted
   
   

Apache 2.4 has changed some of the naming conventions:

The virtual hosts file needs now the .conf extension. Which means instead of depot it is depot.conf

sudo a2ensite depot.conf

Apache 2.4 has change security settings.

If the web application is outside /var/www/, e.g. in the /home directory it is necessary to add the directory to the apache2.conf otherwise you get an authz_core: error "client denied by server configuration: /home/rubys/deploy/depot/public/.

To fix this add to apache2.conf (Ubuntu)

Require all granted

‘//= require jquery.ui.effect-blind’ doesn’t work. Try ‘//= require jquery-ui/effect-blind’ instead.

See stackoverlow - /questions/24819381/application-js-cant-find-jquery-ui-effect-blind

‘//= require jquery.ui.effect-blind’ doesn’t work. Try ‘//= require jquery-ui/effect-blind’ instead.

See stackoverlow - /questions/24819381/application-js-cant-find-jquery-ui-effect-blind

When I toggle between the English and Spanish versions of the store, the “Add to Cart” button text does not change—it always retains its initial value. I’m assuming this is because the buttons are created inside a cache block?

The effect-blind jQuery UI module should be included as follows: `//= require jquery-ui/effect-blind` instead of `//= require jquery.ui.effect-blind`. More information can be found at github: joliss/jquery-ui-rails

After I add the Ajax to make the images clickable, when I click on the image it adds two of the item to my cart.

Dear brilliant writers of this book,

It’s a very minor issue, but I wanted to do something back At Chapter 11. Task F: Add a Dash of Ajax, when implementing the Yellow Fade Technique, you’re asking us to require jquery.ui.effect-blind. For me that didn’t work (resulted in a not-found error). I had to change it to: jquery-ui/effect-blind.
As I said, very minor but maybe still handy for future readers :)

Cheers,

Abel

Footer link 3 to Coffee Script is no longer valid, leads to 404 error page. Suggest updating to coffeescript.org.

In the code change for Download rails40/depot_m/app/assets/javascripts/application.js, the changed line:

//= require jquery.ui.effect-blind

is no longer valid. The line must be changed to:

//= require jquery-ui/effect-blind

due to changes in the library. See stackoverflow.com/questions/24819381/application-js-cant-find-jquery-ui-effect-blind

Chapter 13 Task H: Sending Mail ends on an unstable note. The reader is not guided to run their tests, and is not guided on how to handle any errors that may crop up in the process.

The file rails40/depot_r/app/controllers/orders_controller.rb directs the user to add the line “OrderNotifier.received(@order).deliver”.

However, with the most recent version of Rails (>4.2), this crops up a warning stating:

“DEPRECATION WARNING: `#deliver` is deprecated and will be removed in Rails 5. Use `#deliver_now` to deliver immediately or `#deliver_later` to deliver through Active Job. (called from block in create at /vagrant/work/depot/app/controllers/orders_controller.rb:43)”

This can by fixed by changing the inserted line to:

“OrderNotifier.received(@order).deliver_now”.

The section that states “the index view doesn’t display notice information” is no longer valid. By default, `rails generate` now adds the following to the top of each show or index view file:

<%= notice %>

It is still nice to add the check that is in the text to not display the notice markup unless there is one.

The suggested changes to _form.html.erb on page 194 of the PDF are missing the arrowsemarking where changes are being added to the existing file.

The user is never directed to add any input to the fields before being directed to click “Create User”. This is confusing, as it jumps directly to “After clicking Create User”, which implies that there’s a missing step that’s been omitted.

The layout for /app/views/sessions/new.html.erb file is missing the “field” classes from the two divs for the login form on the page. This causes the form to render incorrectly.

The line for the store’s index page: <%= sanitize(product.description) %> should be wrapped in a p tag to match the CSS. Using the provided markup makes the description appear under the image.

When image is clicked, items are added to cart twice. Adding `.not(“.clickable”).addClass(“clickable”)` fixed it:

$(document).on “ready page:change”, ->
\tconsole.log(‘ready or page change’)
\t$(“.store .entry > img”).not(“.clickable”).addClass(“clickable”).click ->
\t\tconsole.log(‘image clicked’)
\t\t$(this).parent().find(‘:submit’).click()

The AJAX unit test (test_should_create_line_item_via_ajax) failed with this error:

No JQuery call matches [:html, “#cart”]

To fix, I put the call to assert_select_jquery in a do block attached to assert_response :success

There is a sentence that reads “Now that we have the jQuery-UIjQuery-UI library available”. There are two ‘jQuery-UI’

Working on section 6.2 Iteration A2: Making Prettier Listings…NEED HELP PLEASE!

media.pragprog.com/titles/rails4/code/rails40/depot_a/app/assets/images/

am being denied access to this server. getting error. Forbidden

You don’t have permission to access /titles/rails4/code/rails40/depot_a/app/assets/images/ on this server.

Apache/2.4.7 (Ubuntu) Server at media-origin.pragprog.com Port 80

I would need access to populate the DB with images.

Please advise.

Thank you,
Chris Arzoomanian

When I look at the application in the browser (Chrome) there is no header or sidebar formatting. To be sure I did not make an error, I loaded depot_e, and had the same problem. The menus, the logo, etc is all there, but no header or side bar.

At the top of PDF page 132, we see a line from rails40/depot_i/app/assets/stylesheets/carts.css.scss:

.total_line .total_cell {

There should be a comma after the first class attribute value, ``.total_line’’, making
this really a technical typo, I suppose.

The code block in products_controller.rb is curently:

@update = {
title: ‘Foo Bar’,
description: ‘Foos and bars, bars and foos.’,
image_url: ‘foo.jpg’,
price: ‘19.99’
}

This triggers an exception when running the tests because the test expects an ActiveRecord object. The @update instance var ought to be:

@update = Product.new(
title: ‘Foo Bar’,
description: ‘Foos and bars, bars and foos.’,
image_url: ‘foo.jpg’,
price: ‘19.99’
)

Alternatively, it may be better to just have the reader update the products.yml fixture. This would be a slight digression, but would help explain the @product = products(:one) line of code in the controller.

Let me know what you all think. I’ve been a software engineer using Ruby for a few years and am diving deeper into Rails and wanted a refresher, and I’m enjoying going through this book so far!

The locale switcher snippet creates a form without a method which defaults to POST and thus ends up trying to access an unavailable route. The snippet should be:

<%= form_tag store_path, method: :get, class: ‘locale’ do %>
<%= select_tag ‘set_locale’,
options_for_select(LANGUAGES, I18n.locale.to_s),
onchange: ‘this.form.submit()’ %>
<%= submit_tag ‘submit’ %>
<%= javascript_tag “$(‘.locale input’).hide()” %>
<% end %>

In the OrdersController snippet we localize the thanks message with I18n.t(‘.thanks’) but the following lines suggest you can add the locale message as:

en:
thanks: “Thank you for your order”

The localization will not be found because it expects to find it based on controller name and action i.e.

en:
orders:
create:
thanks: “Thank you for your order”

After rails40/depot_j/app/views/carts/show.html.erb, this sentence appears: “The partial template itself is simply another template file (by default in the same directory as the object being rendered and with the name of the table as the name.” That sentence has a couple of problems. First, to what does “the name of the table” refer? I don’t see any table name. Second, “in the same directory as the object being rendered” doesn’t really make sense. The object being rendered lives in memory (RAM) and is not in a directory on disk. (I’m guessing the intent was to avoid a wordier construct such as “in the same directory as the view templates for the object being rendered”.)

The line <%= render cart %> breaks the controller unit tests badly. The problem is that cart may be nil (for instance, if the URI path is “/carts” (invoking carts#index). The fix is to use this instead:
<% if cart %> <%= render cart %>
<% end %>

Moral of the story: Run unit tests after every change, no matter how trivial. :-)

The <%= hidden_div_if(cart.line_items.empty?, id: 'cart') do %> line also breaks controller unit tests. Again, it is not safe to assume cart is not nil.

Fix: <%= hidden_div_if((cart.nil? or cart.line_items.empty?), id: ‘cart’) do %>