Today I Learned

hashrocket A Hashrocket project

Generate Rails Models with Namespaces

You can use the rails model generator to generate namespaced models. I always have a hard time remembering the syntax for namespaces, but it's pretty straightforward.

Say I want to create a model Blog::Post. The generator for this is:

rails generate model blog/post title:string ...

This will generate the following files (assuming you're using rspec and FactoryBot)

invoke  active_record
create    db/migrate/20241028193321_create_blog_posts.rb
create    app/models/blog/post.rb
create    app/models/blog.rb
invoke    rspec
create      spec/models/blog/post_spec.rb
invoke      factory_bot
create        spec/factories/blog/posts.rb

If the namespace already exists, you'll be prompted to either overwrite or keep the existing app/models/blog.rb file (you'll probably want to keep the existing one).

Happy generating!

Expo Reactive Native Apps on IOS Simulator

With Expo's CLI, the command npx expo run:ios will build and run your application in xcode's IOS simulator. You will need to have Xcode installed in order for the command to work. If you receive an error stating Xcode must be fully installed before you can continue, you may need to navigate to Xcode's settings and set a version of command line tools under the locations tab. image

Create index with migration shorthand in Rails

Using the Ruby on Rails migration generator is great to get up and running but always seems to require just a little bit more effort once the migration file is created.

There is a shorthand syntax for the cli interface of the generator but I can never remember it past a column name and type... so I'm putting this here to remember it for all of us!

To create an index just continue adding a bit more information to your column declaration. Let's start with this as a base so we're on the same page:

rails generate add_name_to_widgets name

This will create this migration:

class AddNameToWidgets < ActiveRecord::Migration[7.0]
  def change
    add_column :widgets, :name, :string
  end
end

Now by making a minor adjustment to the original cli call we can generate the index too:

rails generate add_name_to_widgets name:string:index
class AddNameToWidgets < ActiveRecord::Migration[7.0]
  def change
    add_column :widgets, :name, :string
    add_index :widgets, :name
  end
end

And you know what? We can do unique indexes as well:

rails generate add_name_to_widgets name:string:uniq
class AddNameToWidgets < ActiveRecord::Migration[7.0]
  def change
    add_column :widgets, :name, :string
    add_index :widgets, :name, unique: true
  end
end

Generate non-null field migration in Rails 8

I'm sure many of us are familiar with the Ruby on Rails migration generator... 

rails generate migration add_name_to_widgets name

which generates a migration that looks like so:

class AddNameToWidgets < ActiveRecord::Migration[7.0]
  def change
    add_column :widgets, :name, :string
  end
end

Then to make the name column have a non-null constraint an addition of null: false would be needed:

class AddNameToWidgets < ActiveRecord::Migration[7.0]
  def change
    add_column :widgets, :name, :string, null: false
  end
end

However, now in Rails 8 an adjustment was made to allow this to be done from the generator shorthand

rails generate migration add_name_to_widgets name:string!

By adding the exclamation point after the column type a migration will now be generated as we wanted before but without the additional manual edit:

class AddNameToWidgets < ActiveRecord::Migration[8.0]
  def change
    add_column :widgets, :name, :string, null: false
  end
end

h/t Akshay Khot

PG Cluster Commands in Ubuntu

The postgresql package for Ubuntu includes some useful commands for managing your database cluster. I learned about these today when we upgraded postgres versions on a digital ocean droplet.

The ones that I learned of were -

  • pg_lsclusters for listing the available clusters on the machine and their status
  • pg_upgradecluster OLD_VERSION CLUSTER_NAME for upgrading to a new cluster. If you don't specify the optional -v (new version), it's assumed you want the most recent version you have installed. This handles copying your old conf files to the new version and setting it up on the originally specified port.
  • pg_dropcluster VERSION CLUSTER_NAME for removing a cluster. Optionally you can specify --stop to force a shutdown and delete.
  • pg_createcluster VERSION CLUSTER_NAME which will create a new cluster given the version and name param. The default is to not start this new cluster on creation, but you can optionally specify the --start flag to immediately start the cluster.

https://manpages.ubuntu.com/manpages/trusty/man8/pg_createcluster.8.html https://manpages.ubuntu.com/manpages/trusty/en/man8/pg_dropcluster.8.html https://manpages.ubuntu.com/manpages/trusty/man8/pg_upgradecluster.8.html https://manpages.ubuntu.com/manpages/xenial/en/man1/pg_lsclusters.1.html

String Replace in Javascript

I'm very used to ruby's gsub(pattern, replacement) that does a [g]lobal [sub]stitution on a string - that is, it replaces all occurrences of the pattern in the string. If you wanted to just replace the first occurrence of the pattern you could use sub, but I so rarely need to do that I forgot it existed.

Javascript's equivalent, replace, handles things a little bit differently. So much so I was surprised by it's behavior.

replace(pattern, replacement)

pattern can be a string or a RegExp, but you get different replacement behavior depending on which you use.

  • If pattern is a string, only the first occurrence of pattern will be replaced.
  • If pattern is a RegExp, by default it will replace the first occurrence, unless you pass the global flag to the pattern. So if I wanted to replace asdf in with hjkl in a string, replace(/asdf/, "hjkl") will replace just the first occurrence. To replace all occurrences, it needs to be replace(/adsf/g, "hjkl) (note the global g flag in the regex).

So maybe the moral of the story is to always use a regex (and remember your flags!).

Docs: String.prototype.replace() - JavaScript | MDN

Sigils in Elixir

In Elixir, there's strings "hi" and charlists 'hi'.

You can also use the ~c sigil to denote a charlist - 

~c"hi there"

There's also a word list sigil ~w which behaves similarly to %w in Ruby. It constructs a list of words - 

~w(blue red green)
=> ["blue", "red", "green"]

Also worth mentioning, the ~r sigil for regexes -

"foo" =~ ~r"hashrocket"
=> false

"hashrocket" =~ ~r/hashrocket/
=> true

There's many other sigils in Phoenix and Elixir. Be sure to check out the docs!

h/t to Jack Rosa

https://hexdocs.pm/elixir/sigils.html

Alias Method on a GraphQL Field

A lot of times I find I have to alias a method on a model when I'm exposing it on a GraphQL type. Most often I have to do this with ? methods:

class Post < ApplicationRecord
  def draft?
    ...
  end
end

class PostType < GraphQL::Schema::Object
  field :draft, Boolean, null: false

  def draft
    @object.draft?
  end
end

I want the field to be draft (without the ?), but on it's own the GraphQL Ruby gem can't resolve it to draft?, so I have to add an additional def in the Type class. This works, but it feels clunky.

Turns out you can use the method: option on the field to alias it inline, which I think streamlines things:

class PostType < GraphQL::Schema::Object
  field :draft, Boolean, null: false, method: :draft?
end

Docs

Refetch Query with Apollo GraphQL Client

The Apollo GraphQL client allows you to easily refetch query results, which can come in super handy if you need to refresh data after some user action on the page. You can do this with the refetch function from useQuery:

const { data, loading, refetch } = useQuery(QUERY);

Then if you want to refetch data after a button click, you can:

<button onClick={() => refetch()}>
  Refetch the data!!
</button>

If you defined any variables in the initial useQuery, refetching will re-use those variables, but you can override them as well in the call to refetch:

refetch({ param: "new value" });

If you need to refetch data after a mutation, you can do that too.

Docs

Change Text of Blank Option in a Rails Select Tag

The form helper select tag (ex - f.select) accepts a boolean option for include_blank, which informs the select tag to have an extra blank option. Setting include_blank: true will look like the below - image

But you can also pass a string to include_blank and this will change the text content of the blank option -

<%= f.select :state, options_for_select(state_options), {include_blank: 'Select a State'} %>

image

https://devdocs.io/rails~7.1/actionview/helpers/formtaghelper#method-i-select_tag

casecmp to Compare Strings

Today I learned about casecmp and casecmp? to compare strings in ruby.

casecmp compares the downcase of both strings and returns 1 if the compared string is smaller, -1 if it's larger, and 0 if they are equal (and nil if they can't be compared).

"hashrocket".casecmp("hashrocket") # => 0
"hashrocket".casecmp("hAsHrOcKeT") # => 0
"hashrocket".casecmp("hashrocket123") # => -1
"hashrocket".casecmp("hashrock") # => 1
"hashrocket".casecmp(123) # => nil

casecmp? does the same comparison but just returns a boolean.

"hashrocket".casecmp("hAsHrOcKeT") # => true
"hashrocket".casecmp("hashrock") # => false
"hashrocket".casecmp(123) # => nil

h/t Brian Dunn

Enum Reject vs Filter

If you're anything like me, you regularly forget if Enum.filter/2 keeps elements that return true or filters them out.

Let existence of Enum.reject/2 be your reminder.

reject/2 does the same thing as filter/2 but discards truthy elements instead of keeping them. I wish that filter/2 was renamed to keep/2, then the 2 functions would feel more like logical opposites and perhaps more readable.

Ruby GraphQL Generators

Today I Learned the GraphQL ruby gem includes generators for types, mutations and other fun things.

rails g graphql:object
rails g graphql:input
rails g graphql:interface
rails g graphql:union
rails g graphql:enum
rails g graphql:scalar
rails g graphql:mutation

What's even neater is if the name of thing things you're generating matches an existing ActiveRecord model, it will scaffold all the database columns as fields!

If you have a model Book like:

class Book < ApplicationRecord
  attribute :id
  attribute :author_id
  attribute :title
  attribute :published_at
end

Running the object generator rails g graphql:object Book will produce:

module Types
  class BookType < Types::BaseObject
    field :id, ID
    field :author_id, ID
    field :title, String
    field :published_at, GraphQL::Types::ISO8601DateTime
  end
end

Using Enum Sort with multiple keys

You can sort an enum by multiple keys at once. For example, If we wanted to sort a list of 'Vehicle' structs by type and model at the same time, we could do this:

vehicle_list = [
  %Vehicle{type: "van", model: "Odyssey"},
  %Vehicle{type: "truck", model: "Avalanche"},
  %Vehicle{type: "van", model: "Pacifica"},
  %Vehicle{type: "truck", model: "Bronco"}
]

Enum.sort_by(vehicle_list, &{&1.type, &1.model})
#=>
[
  %Vehicle{type: "truck", model: "Avalanche"},
  %Vehicle{type: "truck", model: "Bronco"},
  %Vehicle{type: "van", model: "Odyssey"},
  %Vehicle{type: "van", model: "Pacifica"},
]

sort_by is first sorting the vehicles by the :type key and then sorting by the :model key.

Easily Update ActiveRecord Enum Values

Today I learned about some nice helper methods for ActiveRecord Enums. You might already know the ? methods to check the value of the enum. There are also ! methods to succinctly set the value of the enum too!

class Post < ActiveRecord::Base
  enum status: {
    draft: 0,
    published: 1
  }
end

post = Post.new
post.published? # => false
post.published! # updates the status to `published`
post.published? # => true

Turn Off Spell Check in Vim

When I'm writing longer form text in vim, I like to turn on spell check. I don't always want spell check on, so I toggle it on manually when I'm in a Markdown or text file: :set spell.

While I always remember how to toggle it on, I never remember how to toggle it off:

:set nospell

It's the same syntax for any setting - if you wanted to turn off incsearch, its :set noincsearch.

Test for String Equality

In Rails, there is an nice and easy interface that can be used to check a string for equality.

To do this, you can use the ActiveSupport::StringInquirer object. Simply initialize it with a string value, like so:

string = ActiveSupport::StringInquirer.new("vanilla")

and now we can just call string#vanilla? to check for equality

string.vanilla?
=> true

string.chocolate?
=> false

Fun fact:
This is how you are able to do Rails.env.production?

H/T: Matt Polito

Time terminal commands

If you enter time before any terminal command, it will output some information about how long the task took to run.

For example, let's run it on these two, crude, simple ruby scripts to see the time difference

# ./million.rb
1_000_000.times do
  2 + 2
end
> time ruby million.rb
ruby million.rb  0.05s user 0.02s system 47% cpu 0.143 total

​

# ./billion.rb
1_000_000_000.times do
  2 + 2
end
> time ruby billion.rb
ruby billion.rb  18.41s user 0.13s system 99% cpu 18.618 total

H/T Matt Polito

Stub Environment Variables in Vitest

You can stub environment variables in Vitest using vi.stubEnv. This will stub the value on process.env and import.meta.env.

You can also reset all env vars back to their original value with vi.unstubAllEnvs.

process.env.COOL_ENV_VAR; // => "test"
import.meta.env.COOL_ENV_VAR; // => "test"

vi.stubEnv('COOL_ENV_VAR', "stubbed");

process.env.COOL_ENV_VAR; // => "stubbed"
import.meta.env.COOL_ENV_VAR; // => "stubbed"

vi.unstubAllEnvs();

process.env.COOL_ENV_VAR; // => "test"
import.meta.env.COOL_ENV_VAR; // => "test"

Docs

Delete the inner content of an HTML tag

After yesterday's TIL, fellow Hashrocketeer Jack Rosa shared with me a few other cool ways to delete things in vim.

My favorite way that he showed me that I never knew existed was using dit.

This deletes all content of the HTML tag you are inside of.

Let's use the following HTML for a couple examples:

1 |<div>
2 |  <h1>Header</h1>
3 |
4 |  <p>
5 |    This is some paragraph text that is <em>emphasized</em> for importance.
6 |  </p>
7 |</div>

If your cursor was anywhere within the <div></div> without being inside of a nested element, the result would be:

1 |<div></div>

If your cursor was anywhere within <em>emphasized</em>, the result would be:

1 |<div>
2 |  <h1>Header</h1>
3 |
4 |  <p>
5 |    This is some paragraph text that is <em></em> for importance.
6 |  </p>
7 |</div>

Conclusion: This is a nice and easy way to clear out html tags quickly.

Add conditional class names

If you want to conditionally add class names in Rails, here is a clean way to do it.

<%= link_to("Some Page", some_path, 
  class: class_names("bg-black text-black", {"text-white": text_visible?})
%>

This takes advantage of the class_names method, which is just an alias for the token_list method.

h/t to Matt Polito.
I always find myself looking up his TIL and figured if I make it myself it will help me retain it. 😅

ISO 8601 Durations

Today I learned that ISO 8601 includes a spec for durations as well as dates and times.

Normally when I think of ISO 8601 I think of dates (2024-05-30) or times (2024-05-30T19:54:14Z).

But it also includes a spec for durations! Super convenient to have a standardized way to represent this, and rails and javascript libraries are able to parse it.

Some examples:

  • 8 hours => PT8H
  • 3.5 hours => PT3H30M
  • 2 months, 1 day => P2M1D
  • 6 years, 5 months, 4 days, 3 hours, 2 minutes, 1 second => P6Y5M4DT3H2M1S

Use ri to Lookup Ruby Docs from the Command Line

Did you know you can look up ruby documentation on Classes and methods from the command line? The slightly elusive ri command does just that. You can pass it an argument of the class/method you want to look up, or you can enter interactive mode without arguments.

$ ri uniq

$ ri Array#compact

$ ri Hash

You can also use it to browse all the pre-defined ruby global variables:

$ ri ruby:globals

Check out the docs or run ri --help to see all it can do.

h/t Brian Dunn

Rerun Only Failed Tests with RSpec

Say you run your entire rspec suite and a couple of tests fail. You make a change that should fix them. How can you quickly rerun those failed tests to see if they're green? It could take minutes to run the whole suite again, and all you care about is 2 tests.

That's where the --next-failure (-n) flag comes in handy. According to the docs it is "Equivalent to --only-failures --fail-fast --order defined)". So you can rerun only your failed specs, and exit immediately if one does fail. You could of course just use --only-failures too, but sometimes it's nice to fail fast.

bundle exec rspec -n

h/t Brian Dunn

Two Types of Ranges in Ruby

Today I learned there are two ways to construct a range in ruby. Using two dots .. creates a range including the start and end values.

(2..5).include?(2) # => true
(2..5).include?(5) # => true

Using three dots ... creates a range including the start value, but not the end value.

(2...5).include?(2) # => true
(2...5).include?(5) # => false

So if we think of them in terms of intervals, (a..b) is a closed interval ([a, b]), and (a...b) is a right half-open interval ([a, b)).

Postgres comparison with null values

When Postgres is running comparisons, any null values will yield null at the end of the comparison. This is because the null is an unknown value that Postgres can't run the comparison against.

Take the following simple example of a users table and query:

create table users (name text, email text);

insert into users (name, email)
  values ('Joe', 'joe@hashrocket.com'),
  ('Rick', null);
  
select * from users where email not like '%gmail.com';
--  name |       email
-- ------+--------------------
--  Joe  | joe@hashrocket.com
-- (1 row)

You'll notice that the Rick user is not returned in the results.

If you want rows with the null value included in your results, you can coalesce the column to an empty string. This allows Postgres to run the comparison against two known values and return the rows with the null values.

select * from users where coalesce(email, '') not like '%gmail.com';
--  name |       email
-- ------+--------------------
--  Joe  | joe@hashrocket.com
--  Rick | ø
-- (2 rows)

Handling exceptions with rescue_from

ActiveSupport has a handy tool for handling exceptions globally in your Rails app. You can use it to catch specific exceptions and provide a centralized way to manage errors across your application, making your code cleaner and more maintainable.

Here is the example from the docs, showcasing how to catch specific exceptions and what method to run when they are caught.
Note: You can also pass it a block as the handler instead.

class ApplicationController < ActionController::Base
  rescue_from User::NotAuthorized, with: :deny_access
  rescue_from ActiveRecord::RecordInvalid, with: :show_record_errors

  rescue_from "MyApp::BaseError" do |exception|
    redirect_to root_url, alert: exception.message
  end

  private
    def deny_access
      head :forbidden
    end

    def show_record_errors(exception)
      redirect_back_or_to root_url, alert: exception.record.errors.full_messages.to_sentence
    end
end

Delete to beginning of current word

If you are typing something in your shell and you need to delete the entire word you're on, instead of pressing backspace repeatedly, you can press ESC + Backspace and this will delete back to the start of the current word you are on.

Example; Say you wanted to delete this whole filepath, or a majority of it. Simply place your cursor at the end (or wherever you want to delete up to) and press ESC + Backspace to delete all the way back to the word vim

vim /i/accidentally/typed/something/big/that/was/incorrect

and it might leave you with something like this

vim /that/was/incorrect

ActiveRecord Reload only Associated Record

Today I learned about some focused reload methods for ActiveRecord Associations.

Let's say I have an Author class that can have one magnum opus.

class Author < ApplicationRecord
  has_one :magnum_opus
end

Now suppose I've instantiated an Author, and his magnum opus gets updated elsewhere. If I try to access that instance's magnum opus again (existing instance, no reloading), I'll get the old cached version:

author = Author.first
author.magnum_opus.title # => "The Dark Tower"

#elsewhere
mo = MagnumOpus.find_by(title: "The Dark Tower")
mo.update title: "The Shining"

author.magnum_opus.title # => "The Dark Tower"

Now to remedy this, we can reload the author:

author.reload.magnum_opus.title # => "The Shining"

But why reload the whole author when you can reload just the association? ActiveRecord has reload_* methods for each has_one and belongs_to association that does just that - it reloads only the associated record.

author.reload_magnum_opus.title # => "The Shining"

Docs for has_one and belongs_to.

h/t Matt Polito

Markdown alert style content blocks on Github

Use special markdown to emphasize content inside alert style content blocks on Github.

> [!NOTE]  
> Highlights information that users should take into account, even when skimming.

> [!TIP]
> Optional information to help a user be more successful.

> [!IMPORTANT]  
> Crucial information necessary for users to succeed.

> [!WARNING]  
> Critical content demanding immediate user attention due to potential risks.

> [!CAUTION]
> Negative potential consequences of an action.

image

Find Missing Relations Easily with .missing

It can be kind of clunky to query ActiveRecord for records where the has_manyassociation is empty.

Say I have an Author class that has many Books. One way to query for Authors without books is the following:

class Author < ApplicationRecord
  has_many :books
end

Author.left_joins(:books).where(books: {id: nil})

This totally works, but at least for me is difficult to reason what we're querying. However, Rails 6.1 added a .missing method that really helps clarify what the query is doing:

Author.where.missing(:books)

Much clearer - this will grab all authors that do not have any books.

Docs for further reading. Happy querying!

Set Attributes when Creating with .create_with

You can set attributes to be used when creating new records with .create_with:

Author.create_with(name: "Hashrocketeer")
Author.new.name # => "Hashrocketeer"

This can be particularly useful if you're doing a .find_or_create_by and want to set some values only when creating:

Author
  .create_with(post_count: 0)
  .find_or_create_by(name: "Hashrocketeer")

This will find an author with name "Hashrocketeer". If we find an existing Author, we won't change their post_count. If we don't find an existing Author, we'll create one with a post_count of 0.

Read more in the docs

Use comm to Compare Files

Today I learned about comm, which is used to select the common lines in two files. It's pretty neat, but has a strange output format.

Say we have two text files:

# first.txt
one
two
three

# second.txt
one
three
four

We can run the below command to find the common lines. In the output, the first column is what's only in first.txt, the second column is what's in second.txt, and the third column is what's common.

$ comm first.txt second.txt                                                                                         
                one
        three
        four
two
three

Hmm, that doesn't look right - one and three are common, not just one. The caveat with comm is that the files need to be sorted lexically. You can sort easily in bash with bird beak notation for process substitution.

$ comm <(sort first.txt) <(sort second.txt)
        four
                one
                three
two

If we only want the common lines, we can apply the flags -12 to hide the first and second columns:

$ comm -12 <(sort first.txt) <(sort second.txt)
one
three

Add metadata to Stripe webhooks using TwiML <Pay>

This is kind of a specific TIL, but hopefully it saves somebody else the time it took me to find the answer.

If you are using the TwiML <Pay> verb there is a noun on <Pay> called <Parameter> which lets you pass parameters to your action.

If your payment provider is Stripe and you want to send custom metadata, you can send a <Parameter> with a name prefaced as metadata_ and it will be added to the Stripe metadata that gets sent out in the webhook.

Here's an example:

<Pay paymentConnector="stripe"> 
   <Parameter name="metadata_testKey" value="value" /> 
</Pay>

and now the object you receive in your webhook will have the following:

"metadata": {
  "testKey": "value"
}

Modify Tables with `change_table` in Rails

Ever since I used ecto in Elixir Phoenix, I've always thought about their alter table function while working on Rails projects. Turns out, I have been living under a rock and I could have been using change_table this whole time 🤦🏻‍♂️

For those new to the change_table function, it allows you to make bulk alterations to a single table with one block statement. You can adjust columns(and their types), references, indexes, indexes, etc. For a full list of transformations, see the official api documentation.

If you're using Postgres or MySQL, you can also add an optional argument bulk: true and it will tell the block to generate a bulk SQL alter statement.

class AddUserIdToPosts < ActiveRecord::Migration[7.1]
  def change
    change_table(:posts, bulk: true) do |t|
      t.remove_reference :user_post, :text, null: false
      t.references :user, null: false
    end
  end
end

API Ruby on Rails - change_table

Hooray Rails! 🥳