Today I Learned

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9 posts by koriroys @koriroys

accepts_nested_attributes_for in Rails 5.2

Getting accepts_nested_attributes_for to work can be a bit tricky, and most of the walkthroughs I found are a bit dated, so here’s a quick update.

Our models will be User and Address:

class User < ApplicationRecord
  has_many :addresses
  accepts_nested_attributes_for :addresses
end

class Address < ApplicationRecord
end

Now, assuming we have a UsersController, with all the standard resource actions omitted, we try to add addresses to our permitted params:

class UsersController < ApplicationController
  def user_params
    params.require(:user).permit(:name, :email, :addresses)
  end
end

Logically this seems like it would work, but if we look in the rails server logs, we will see:

Unpermitted parameter: :addresses_attributes

So we add it to our permitted params:

  def user_params
    params.require(:user).permit(:name, :email, :addresses_attributes)
  end

and refresh. Lo and behold, we get the same error!

Unpermitted parameter: :addresses_attributes

The secret is that address_attributes is a hash, and we need to communicate that to Rails:

  def user_params
    params.require(:user).permit(:name, :email, addresses_attributes: {})
  end

Et voilà!

Rails Collection#exists?

I’ve been using Rails for almost a decade, and find I still don’t know even close to all it has to offer. Today, I was browsing through an open source app, and stumbled across this code:

unless feed.posts.exists?(@post.id)
  feed.posts << @post
end

I’d never seen or used exists? on a collection before, so I looked it up. And of course, there it is, right in the Rails Guides Association Basics - methods added by has many!

Digging in a bit, what arguments can exists? take? Here’s the reference.

Turns out there a lot of options!. Integer, string, array, hash, false, or no args.

Well that’s kinda neat! So what does the no args do?

Imgur

It seems to behave similar to any?, and return true if there are any members of the collection, false if it’s empty.

TLDR: Read the Rails Guides. A decade in, you’ll probably still learn something!

VSCode Select All Matches

I’ve been using VSCode for a while, and really love the shortcut CMD+Shift+D: if you have something selected, it will find and select the next match.

Imgur

Today I accidentally pressed CMD+Shift+L, and serendipitously found out that it “Selects All Occurrences of Find Match.” Now I can remove those pesky quotations marks in this Ruby hash all at once! As written, the hash keys will be turned into symbols anyway, so the quote marks are noise.

Imgur

Hat tip 🎩to Licecap for straightforward recording of gifs on any platform.

Ruby 2.7 Enumerable#tally

Have you ever wanted to get back a count of how often objects showed up within an array? If so, you’ve likely written (or copy-pasta’d) some variation of the code below:

list = %w(red red red blue blue fish blue blue)

list.each_with_object(Hash.new(0)) { |v, h| h[v] += 1 }          # => {"red"=>3, "blue"=>4, "fish"=>1}
list.each_with_object({}) { |v, h| h[v] ? h[v] += 1 : h[v] = 1 } # => {"red"=>3, "blue"=>4, "fish"=>1}
list.group_by { |v| v }.map { |k, v| [k, v.size] }.to_h          # => {"red"=>3, "blue"=>4, "fish"=>1}

Lucky for us, Ruby 2.7 introduces a new convenience method in Enumerable#tally, so our above code reduces to:

list = %w(red red red blue blue fish blue blue)
list.tally # => {"red"=>3, "blue"=>4, "fish"=>1}

Huzzah!

You can read the feature discussion here!

Ruby Array#sort_by

Let’s say we have the following list of very interesting items.

items = [
  { name: "dogfood", price: 4.99 },
  { name: "catfood", price: 5.99 },
  { name: "batfood", price: 4.99 }
]

Our client wants the list sorted by price descending, and we should break ties in price by then sorting by item name descending. So with our example list, the result should be:

items = [
  { name: "batfood", price: 4.99 },
  { name: "dogfood", price: 4.99 },
  { name: "catfood", price: 5.99 }
]

Here’s a method that does the job for our client:

def sort_by_price_and_name(items)
  items
    .group_by { |i| i[:price] }
    .map { |_k,v| v.sort { |a, b| a[:name] <=> b[:name] } }
    .flatten
end

It’s a bit unwieldy and inelegant. It turns out there is a perfect method for this in Ruby:

def sort_by_price_and_name(items)
  items.sort_by { |i| [i[:price], i[:name]] }
end

Ruby’s Enumerable#sort_by works in this case where we sort by all the fields in ascending order. If we wanted to sort by price ascending, then name descending, sort_by would no longer be the tool we’d want to use.

Hat tip to @joshcheek for the knowledge.

Useful Git Diff Filenames

If you type git config --global diff.noprefix true into your terminal, it will set the value like so in your ~/.gitconfig file:

[diff]
    noprefix = true

The upshot is that git diffs will no longer prefix files with a/ and b/, such that you can copy a useful path when you double-click to select it in the terminal.

--- a/file/that/changed.awesome
+++ b/file/that/changed.awesome

becomes

--- file/that/changed.awesome
+++ file/that/changed.awesome

Credit to @brandur for the tip. Here’s the source tweet

Migrating to form_with

Whilst upgrading a Rails application from 4.1 to 5.2, my feature specs started throwing a strange error:

Unable to find field "X" that is disabled (Capybara::ElementNotFound)

I reverted my changes… the tests passed. Step 1 in debugging: read the error message. Capybara is saying the element I’m trying to find is disabled. If I inspect the html generated by form_for:

= form_for book do |f|
  = f.label :title, 'Title'
  = f.text_field :title
  = f.button 'Save Changes', type: :submit
<form action="/books/14" accept-charset="UTF-8" method="post">
  <label for="book_title">Title</label>
  <input type="text" name="book[title]" id="book_title">
  <button name="button" type="submit">Save Changes</button>
</form>

and compare it to the html generated by form_with:

= form_with model: book, local: true do |f|
  = f.label :title, 'Title'
  = f.text_field :title
  = f.button 'Save Changes', type: :submit
<form action="/books/14" accept-charset="UTF-8" method="post">
  <label for="book_title">Title</label>
  <input type="text" name="book[title]">
  <button name="button" type="submit">Save Changes</button>
</form>

Notice what’s missing. form_with does not automatically generates ids for form elements, and the id is necessary to link the label’s for with the input’s id, otherwise fill_in('Title', with: "Pride and Prejudice") doesn’t work in Capybara. Either add the ids manually, or in Rails 5.2 use this setting:

Rails.application.config.action_view.form_with_generates_ids = true