Logo

TODAY I LEARNED

78cd308de04ac7b78a779f7092b7411e

19 posts by Edwin Cruz
@softr8

Using Gem::Dependency class manually to ensure version matching

I needed to add a mechanism to ensure that some actions of a controller were available only for specific versions, and I thought it was super similar of what Gemfile does, so I started to look how to use Gem::Dependency to solve this, and turns out it was super easy:

class Controller
  def feeds_one
    check_for_version_support('>= 1.0', '< 3')

    render json: SomeData.all
  end

  def feeds_two
    check_for_version_support('= 1.0')

    render json: SomeData.all
  end

  def feeds_three
    check_for_version_support('>= 2.1')

    render json: SomeData.all
  end

  private

  def check_for_version_support(*specification)
    checker = Gem::Dependency.new(action_name, specification)

    return if checker.match?(action_name, params[:version])

    raise VersionNotSupported, "Version not upported"
  end
end

Learned by Edwin Cruz on Apr 7, 2021

973983 adforcodereview v3 0211021 c02 021121

Using Upsert with Rails

Some DBMS support natively something that behaves like update or insert, Rails recently added the method Upsert that can take advantage of this method.

It is useful to update information that do not need to run validations, meaning, in a super performant way, here's an example:

# We usually do this:
activity = current_user.activity
if activity 
  activity.update(last_seen_at: Time.current)
else
  current_user.activity.create(last_seen_at: Time.current)
end

But if you see, it does not need to run any validation, it just needs to update last_seen_at if exists or create a new one, it performs two queries: one to instanciate the activity object and a second one that performs the real update/insert statement.

That can be replaced with the following code and it will perform just a single query and it will take care to either create the record or update an existing one

Activity.upsert({ last_seen_at: Time.current, user_id: current_user.id}, unique_by: :user_id)

To make this really work, considering you use Postgresql, you have to add a unique index on user_id and modify default value on created_at and updated_at in a migration like this:

query = <<-SQL
  ALTER TABLE #{Activity.table_name}
  ALTER COLUMN created_at SET DEFAULT CURRENT_TIMESTAMP,
  ALTER COLUMN updated_at SET DEFAULT CURRENT_TIMESTAMP
SQL
execute(query)

Learned by Edwin Cruz on Mar 19, 2021

973983 adforcodereview v3 0211021 c02 021121

Better usage of Rails logger

Logging usefull data is a hard task, but there's one specific method that helps to improve the experience of logging actual useful information: tagged. It adds extra tags to the log message making it easy to debug:

Rails.logger.tagged('Super App') do
  Rails.logger.info('Log Message')
end

This will result in somethin like this:

[Super App] Log Message

If you can see, it prepends usefull information, you could add personalized data to trace logs, for example:

class ApplicationController << ActionController::Base
  around_action :add_logger_tags

  def add_logger_tags
    Rails.logger.tagged(logging_tags) do
      yield
    end
  end

  def logging_tags
    [
      "Request Id: #{request.id}",
      "Session Id: #{session.id}",
      current_user && "User id: #{current_user.id}"
    ]
end

And you will have super nice logs to read

Learned by Edwin Cruz on Mar 18, 2021

973983 adforcodereview v3 0211021 c02 021121

Creating an infinite loop in Ruby

If you need to iterate over a collection that its size is unknown, you can create an infinite loops in ruby easily, but if you need an index, then there's this option:

(1..).each do |page|
  results = ExternalService.get('/endpoint', page: page)
  parsed = JSON.parse(response.body)
  break if parsed['data'].empty?

  process_data(parsed['data'])
end

Learned by Edwin Cruz on Mar 16, 2021

973983 adforcodereview v3 0211021 c02 021121

Count similar items in an array in Ruby

Before ruby 2.7, you would have to do some hacky code like:

array.inject({}) {|f, v| f[v] ||= 0; f[v] += 1 ; f }

But starting with Ruby 2.7, there's a nicer way:

array.tally
irb: [1, 2, 3, 4, 4, 5, 5].tally
=> {1=>1, 2=>1, 3=>1, 4=>2, 5=>2}

Learned by Edwin Cruz on Mar 11, 2021

973983 adforcodereview v3 0211021 c02 021121

Printing queries executed by ActiveRercord

Starting of Rails 6, there's a handy way to specify the level of verbocity to ActiveRecord queries:

ActiveRecord::Base.verbose_query_logs = true

Full documentation here

No more adding a custom logger to ActiveRecord::Base.logger

Learned by Edwin Cruz on Mar 11, 2021

973983 adforcodereview v3 0211021 c02 021121

Updating ActiveRecord models without loading an instance using Postgresql

There're sometimes that we need to update an ActiveRecord Model but it is not necesary to load an instance, the normal flow would be the following:

profile = UserProfile.find_by(user_id: id)
profile.update(last_seen_at: Time.now)

The problem with this is that we load a useless instance of UserProfile, it is not needed, in a high traffic sites, an extra select query can count a lot, but luckly, Rails has addressed this with upsert command:

UserProfile.upsert({ last_seen_at: Time.now, user_id: id }, unique_by: :user_id)

This will use native Postgresql upsert command to update a record if it exists or insert a new one and no select will be performed, everything in a single query instead of two.

To make it really work, you need to modify your created_at and updated_at columns to have default current_timestamp

Learned by Edwin Cruz on Mar 10, 2021

973983 adforcodereview v3 0211021 c02 021121

Using Rails to migrate columns from JSON to JSONB in Postgresql

Postgres offers data type json to store any structure easily, but one dissadvantage is that filtering by properties stored in the json column are super slow, one simple fix before refactoring the whole implementation is to migrate the column to be jsonb, since it is stored in binary form, it supports indexes, a easy and safe way to do it is as follows:

class ModifyJSONDataDataType < ActiveRecord::Migration[6.0]
  def up
    add_column :table_name, :data_jsonb, :jsonb, default: '{}'

    # Copy data from old column to the new one
    TableName.update_all('data_jsonb = data::jsonb')

    # Rename columns instead of modify their type, it's way faster
    rename_column :table_name, :data, :data_json
    rename_column :table_name, :data_jsonb, :data
  end

  def down
    safety_assured do
      rename_column :table_name, :data, :data_jsonb
      rename_column :table_name, :data_json, :data
    end
  end
end

Then, using another migration(due the ability to disable transactions), add an index to it

class AddIndexToDataInTableName < ActiveRecord::Migration[6.0]
  disable_ddl_transaction!

  def change
    add_index :table_name, :data, name: "data_index", using: :gin, algorithm: :concurrently

    # You can even add indexes to virtual properties:
    # add_index :table_name, "((data->'country')::text)", :name => "data_country_index", using: 'gin', algorithm: :concurrently
  end
end

Learned by Edwin Cruz on Mar 8, 2021

973983 adforcodereview v3 0211021 c02 021121

Inserting images in markdown posts

If you want to insert an image inside a markdown body, you can do it with:

![alt text](https://cdn.host.com/image.png "Title")

Example: MagmaLabs

Learned by Edwin Cruz on Mar 4, 2021

973983 adforcodereview v3 0211021 c02 021121

Invoking ActiveRecord::Migration functions in command line

If you need for some weird reason, to run migration commands in your rails console, just do the following:

ActiveRecord::Migration.add_index :table, :col, name: 'col_index'

Learned by Edwin Cruz on Mar 2, 2021

973983 adforcodereview v3 0211021 c02 021121

Native Pub/Sub in Rails with ActiveSupport::Notifications

If you want to use pub/sub design pattern inside your rails app, there's no need to add extra dependencies, you can use ActiveSupport::Notifications to do the job

Example:

class Order
  # methods

  def complete
    update(complted_at: Time.zone.now, etc: 'some')
    ActiveSupport::Notifications.instrument("order_completed", { number: order.number })
  end
end

module Subscribers
  class SendConfirmationEmail
    def self.subscribe!
      ActiveSupport::Notifications.subscribe("order_completed") do |_name, _start, _finish, _id, params|
        order = Order.find_by number: params[:number]
        OrderMailer.confirm_order(order).deliver_later
      end
    end
  end
end

module Subscribers
  class UpdateCustomerCRM
    def self.subscribe!
      ActiveSupport::Notifications.subscribe("order_completed") do |_name, _start, _finish, _id, params|
        order = Order.find_by number: params[:number]
        CrmIntegration.update_customer(order.customer.email, order.total_amount)
      end
    end
  end
end

# etc

Learned by Edwin Cruz on Mar 1, 2021

973983 adforcodereview v3 0211021 c02 021121

Rails find_by using relationships

If you want to find records via a relationship you can do it easily:

product = Product.joins(:variants).find_by(variants: { sku: 'SKU' }

Instead of:

product = Variant.find_by(sku: 'SKU')&.product

Learned by Edwin Cruz on Mar 1, 2021

973983 adforcodereview v3 0211021 c02 021121

Measuring memory utilization

Ruby comes with the cool module Benchmark, but the only downside is that it only provides the time taken for each task.

A simple approach to get how many memory the ruby process is consuming is to call: ps -o rss:

memory_before = `ps -o rss= -p #{$$}`.to_i
Utils.heavy_memory_consumming_process
memory_after = `ps -o rss= -p #{$$}`.to_i

puts "The process took #{memory_after - memory_before} KB"

Learned by Edwin Cruz on Mar 1, 2021

973983 adforcodereview v3 0211021 c02 021121

Editing a file using cat

If you have to modify a file because any editor is present (vi, vim, nano, etc). you can use cat to do it:

$ cat > filename.ext
write or paste the content

ctrl+d

And that would be it! Super helpful when debugging flaky tests that only fail in the CI server

Learned by Edwin Cruz on Feb 24, 2021

973983 adforcodereview v3 0211021 c02 021121

When to eager load relationships in Rails and when it is not that good

Rails provides a way to eager load relationships when fetching objects, the main idea is to avoid queries N+1, but, when isn't a good idea when to do it?

Good

When rendering unique results that can not be cached, for example: table reports

Why? Most of the times you need to display related information

orders = Order.includes(:user, :line_items).completed

Try to avoid

When you use fragment cache

Why? Eager load is executed before the rendering, regardless the final result is already cached or not. If using eager loading, it will always be executed, but when allowing queries n+1 that query will be executed once to fill the cache, and that's it

products = Product.includes(:categories, variants: [:price]).search(keywords)

Use product.id & updated_at to fill a fragment cache and fetch the data from database only when needed, no extra info needed such as variants, categories, prices, etc

Learned by Edwin Cruz on Feb 19, 2021

973983 adforcodereview v3 0211021 c02 021121

Connecting Ruby to AWS IoT Core using MQTT client

If you need to use Ruby to connect to Aws Iot Core, this is all you need:

require 'aws-sdk-iot'
require 'aws-sdk-secretsmanager'
require 'json'
require 'mqtt'

secrets_manager = Aws::SecretsManager::Client.new(
    region: ENV["IOT_AWS_REGION"],
    access_key_id: ENV["IOT_AWS_ACCESS_KEY"],
    secret_access_key: ENV["IOT_AWS_SECRET_ACCESS_KEY"]
    )

client = Aws::IoT::Client.new(
    region: ENV["IOT_AWS_REGION"],
    access_key_id: ENV["IOT_AWS_ACCESS_KEY"],
    secret_access_key: ENV["IOT_AWS_SECRET_ACCESS_KEY"]
    )

# Creates new ssl certificate
cert = client.create_keys_and_certificate(set_as_active: true)

# A policy named iot-mqtt needs to exist with permissions to publish and read
# any topic names
client.attach_policy(policy_name: "iot-mqtt", target: cert.certificate_arn)

# Stores the certificate in aws secrets manager
secrets_manager.create_secret(name: "iot_cert_pem", secret_string: cert.certificate_pem)
secrets_manager.create_secret(name: "iot_private_key", secret_string: cert.key_pair.private_key)

# Reads the certificate from aws secrets manager
cert_pem = secrets_manager.get_secret_value(secret_id: "iot_cert_pem").secret_string
private_key = secrets_manager.get_secret_value(secret_id: "iot_private_key").secret_string

# Connects to aws iot core endpoint using mqtts
mqtt_client = MQTT::Client.new(ENV["IOT_AWS_ENDPOINT"])
mqtt_client.cert = cert_pem
mqtt_client.key = private_key
mqtt_client.connect(MQTT::Client.generate_client_id("my-awesome-app-"))

# Publishes a message
message = { desired: { speed_limit: 35 } }
mqtt_client.publish("$aws/things/sensor_home/shadow/update", { state: message }.to_json)

# Listens to all accepted shadow updates
mqtt_client.get("$aws/things/+/shadow/+/accepted") do |topic, message|
    payload = JSON.decode(message)
    puts "Got #{topic}"
    puts "With #{payload}"
end

Learned by Edwin Cruz on Feb 11, 2021

973983 adforcodereview v3 0211021 c02 021121

Getting Postgres version using rails console

If you are not sure what PG version your environment is using, execute this in the rails console:

ActiveRecord::Base.connection.select_value('SELECT version()')

Learned by Edwin Cruz on Feb 11, 2021

973983 adforcodereview v3 0211021 c02 021121

Stubbing a block in rspec

There're at least two ways to stub a block in rspec, the first version is using and_yield

config = double('Config', enabled: true)
allow(app).to receive(:config).and_yield(config)
app.config do |config|
  expect(config.enabled).to be_truthy
end

The second version is receiving the block

config = double('Config', enabled: true)
allow(app).to receive(:config) do |_, &block|
  block.call(config)
end|
app.config do |config|
  expect(config.enabled).to be_truthy
end

Learned by Edwin Cruz on Feb 10, 2021

973983 adforcodereview v3 0211021 c02 021121

How to see the full backtrace when running rspec

If you need to see the full backtrace of your tests, all you need to do is to add --backtrace to the command:

bundle exec rspec spec/model/user_spec.rb --backtrace

Learned by Edwin Cruz on Feb 10, 2021

973983 adforcodereview v3 0211021 c02 021121