Forem: Dmitry Voronov

How to use Rails translations for Reform attributes

Dmitry Voronov — Mon, 16 Sep 2019 19:19:00 +0000

If you use Reform for the form objects and want the translations in your Rails application to work as with ActiveRecord objects, then you can add ActiveModel::Translation module to the form class or base class and specify the method with the key to translations.

class BaseForm < Reform::Form
  extend ActiveModel::Translation

  def self.i18n_scope
    :forms
  end
end

class UserForm < BaseForm
  feature Coercion

  property :login
  property :change_password, virtual: true, type: Types::Form::Bool
  property :password
  property :password_confirmation

  validation do
    required(:login).filled
  end

  validation if: ->(_) { change_password } do
    required(:password).confirmation
  end
end

Set translations for form fields.
You can move them to a new file config/locales/forms.yml.

en:
  forms:
    attributes:
      user_form:
        login: Enter login
        change_password: Change password?
        password: Enter password
        password_confirmation: Confirm password

Now, translations will be used by the simple form or you can call them manually by UserForm.human_attribute_name.

How to store large JSON in PostgreSQL with Rails Attributes API

Dmitry Voronov — Wed, 28 Aug 2019 10:58:43 +0000

If you store large objects in the database (such as JSON), for example, data for big reports, then this can take up a lot of space. To reduce the size of data, you can compress and store in binary form.

PostgreSQL has a bytea field type for storing such data. You can add bytea column in Rails using migration

add_column :reports, :data, :binary

For binary field operations, you can use the Rails Attributes API and add a new BinaryHash data type

# app/types/binary_hash.rb

class BinaryHash < ActiveRecord::Type::Binary
  def serialize(value)
    super value_to_binary(value.to_json)
  end

  def deserialize(value)
    super case value
          when NilClass
            {}
          when ActiveModel::Type::Binary::Data
            value_to_hash(value.to_s)
          else
            value_to_hash(PG::Connection.unescape_bytea(value))
          end
  end

  private

  def value_to_hash(value)
    JSON.parse(
      ActiveSupport::Gzip.decompress(value),
      symbolize_names: true
    ) || {}
  end

  def value_to_binary(value)
    ActiveSupport::Gzip.compress(value)
  end
end

# config/initializers/types.rb

ActiveRecord::Type.register(:binary_hash, BinaryHash)

And add to binary type attribute in model

# app/models/snapshot.rb

class Reports < ApplicationRecord
  attribute :data, :binary_hash
end

Tests show that data size is reduced by almost 3 times

Run time with 100000 width JSON
                           user     system      total        real
Compress JSON          0.008671   0.001535   0.010206 (  0.010885)
Decompress JSON        0.001357   0.000095   0.001452 (  0.001509)

json size       95450 bytes
binary size   33868 bytes
~ 2.82 times compression

A simple way to distribute jobs in Sidekiq queues

Dmitry Voronov — Mon, 26 Aug 2019 12:16:25 +0000

This option implies that jobs of one context are executed sequentially in one queue, and jobs of different contexts in parallel in different queues.

Let's look at the following example.
There are investment funds for which we want to make time-consuming reporting calculations. Jobs for calculation within the same fund are carried out sequentially so that there are no errors in the calculations, jobs of different funds are performed in parallel.

We automate the distribution of jobs in queues so as not to specify a queue manually.
Specify the queues in the sidekiq.yml configuration file:

:queues:
  - fund_processor_0
  - fund_processor_1
  - fund_processor_2
  - fund_processor_3
  - fund_processor_4

It is important that the queues are numbered from 0.

Now, when starting the worker, we indicate in which queue we will set the job depending on the fund. To do this, we use the operation of obtaining the remainder from dividing the fund ID and the count of queues. So we get the queue number.

# 5 queues
# fund ID % count of queues = queue number
# 1 % 5 => 1
# 2 % 5 => 2
# 3 % 5 => 3
# 4 % 5 => 4
# 5 % 5 => 0
def queue_name(fund_id)
  queue_number = fund_id % 5
  "fund_processor_#{queue_number}"
end

Start the worker, indicating to him the received queue name.
This can be done using the Sidekiq API

Sidekiq::Client.push(
  'queue' => queue_name(fund_id),
  'class' => Fund::ReportCalculator,
  'args' => [fund_id]
)

Create factory with an uploaded file in Rails rspec

Dmitry Voronov — Wed, 03 Jul 2019 14:45:49 +0000

To create a factory with an uploaded file in Rails rspec, needs to be included ActionDispatch::TestProcess module in the rails_helper.rb file to use the #fixture_file_upload method in the factories.

# spec/rails_helper.rb
include ActionDispatch::TestProcess

In a factory, when setting the attribute value, use the method #fixture_file_upload, specifying the path and file type.

# spec/factories/import_file.rb
FactoryBot.define do
  factory :import_file, class: ImportFile do
    data { fixture_file_upload 'spec/fixtures/test_file.pdf', 'application/pdf' }
  end
end

Use hash or case-statement in Ruby?

Dmitry Voronov — Wed, 03 Jul 2019 14:45:34 +0000

Often, when we need to get a value based on the other one, we're using a case-statement. Like this

def realizing_trade_type(realizable_trade_type)
  case realizable_trade_type
  when 'buy'
    'sell'
  when 'short'
    'cover'
  when 'buy_contract'
    'sell_contract'
  when 'short_contract'
    'cover_contract'
  end
end

But, if the conditions and the results are simple values, why don't we use hash for this? We can :)

REALIZING_TRADE_TYPES = {
  'buy'            => 'sell',
  'short'          => 'cover',
  'buy_contract'   => 'sell_contract',
  'short_contract' => 'cover_contract'
}.freeze

Here is the benchmark of both options, executed 10_000_000 times. It shows that a hash is faster in times for such the kind of usage.

>> require 'benchmark'
true
>> Benchmark.bm(15) do |x|
  x.report('hash') { 10_000_000.times { REALIZING_TRADE_TYPES['buy'] } }
  x.report('case-statement') { 10_000_000.times { realizing_trade_type 'buy' } }
  x.report('empty') { 10_000_000.times {} }
end
                      user     system      total        real
hash              0.990423   0.003412   0.993835 (  1.057612)
case-statement    1.752263   0.004531   1.756794 (  1.762030)
empty             0.380810   0.000728   0.381538 (  0.382153)

So, it's better to use a hash when you are just retrieving some values (like in the example above). If there is additional logic to execute, a case-statement is still a way to go.

Render and combine PDF files into one

Dmitry Voronov — Wed, 03 Jul 2019 14:45:27 +0000

Render PDF files from HTML templates in Rails can be done using WickedPDF.

First you need to use ActionView to render HTML to a string:

def render_to_string(data)
  action_view = ActionView::Base.new
  action_view.view_paths = ActionController::Base.view_paths

  action_view.class_eval do
    include ApplicationHelper
    include PDFHelper
    # or other helpers
  end

  action_view.render template: 'pdf/template.html',
                     layout: 'layout/pdf.html',
                     locals: { data: data }
end

Then you can render pdf with the desired settings like this:

# first pdf file with some view settings and values from data1...
pdf1 = WickedPdf.new.pdf_from_string(
        render_to_string(data1), {
            pdf: 'report1',
            page_size: 'Letter',
            orientation: 'Portrait'
        })
# ...and second pdf file with some view settings and values from data2
pdf2 = WickedPdf.new.pdf_from_string(
        render_to_string(data2), {
            pdf: 'report2',
            page_size: 'Letter',
            orientation: 'Landscape'
        })

And now you can combine it with CombinePDF gem, that provide you parse method to get PDF content and to_pdfmethod to render the result back to PDF.

combiner = CombinePDF.new
combiner << CombinePDF.parse(pdf1)
combiner << CombinePDF.parse(pdf2)
combiner.to_pdf

Use image files from S3 in WickedPdf

Dmitry Voronov — Wed, 03 Jul 2019 14:45:21 +0000

If you need to use image files from S3 in your generated pdf file using WickedPdf, then you need first to download the image. You can create method that does this and add it to the helper.

require 'open-uri'

module PdfHelper
  def embed_remote_image(url, content_type)
    asset = open(url, "r:UTF-8", &:read)
    base64 = Base64.encode64(asset.to_s).gsub(/\s+/, "")
    "data:#{content_type};base64,#{Rack::Utils.escape(base64)}"
  end
end

And use image_tag instead of wicked_pdf_image_tag

= image_tag embed_remote_image(file.logo_url, 'image/jpeg')

Manage Elixir versions like RVM & Rbenv

Dmitry Voronov — Wed, 03 Jul 2019 14:45:16 +0000

You can install different versions of the Elixir with help of Kiex, like in Ruby with a RVM and Rbenv.

Download and install Kiex

\curl -sSL https://raw.githubusercontent.com/taylor/kiex/master/install | bash -s

bash

In .bashrc (or .zshrc if you use z shell), add the following

[[ -s "$HOME/.kiex/scripts/kiex" ]] && source "$HOME/.kiex/scripts/kiex"

bash

Install required Elixir

kiex install 1.7 # or another version

bash

And then you can use any version

kiex use 1.7

bash

How to create zip files on the fly w/o Tempfile

Dmitry Voronov — Wed, 03 Jul 2019 14:45:05 +0000

There are many articles about how to archive files from the server and send a zip-file to a client without persisting it on the server. But usually they don't literally do it, because they use temporary files.

There is a simple way to do it without creating any file though. You just have to put files directly to Zip::OutputStream and then read from it. Btw pay attention: you must rewind the stream before reading it.

# some files objects
def download(files)
  zip_stream = Zip::OutputStream.write_buffer do |zip|
    files.each.with_index(1) do |file, index|
     # file name must be uniq in archive
      zip.put_next_entry("#{file.name}--#{index}.#{file.extension}")
      zip.write(file.read.force_encoding('utf-8'))
    end
  end
  # important - rewind the steam
  zip_stream.rewind
  send_data zip_stream.read, 
            type: 'application/zip', 
            disposition: 'attachment', 
            filename: 'files-archive.zip'
end

How to delete polymorphic models cascade

Dmitry Voronov — Wed, 03 Jul 2019 14:44:30 +0000

If you use a polymorphic model in your Rails application, like in example

class Trade < ActiveRecord::Base
  has_many :gl_entries, as: :source, dependent: :destroy
end

class GlEntry < ActiveRecord::Base
  belongs_to :source, polymorphic: true
end

You will not be able to add the usual foreign keys for cascading delete records. But this can be implemented using a database.

To do this, you need to write a trigger in the database that will run the delete function for each record.

CREATE FUNCTION deleteGlEntriesOfTrade()
  RETURNS TRIGGER
  SET SCHEMA 'public'
  LANGUAGE plpgsql 
  AS $$
  BEGIN
    DELETE FROM gl_entries WHERE source_id = OLD.id AND source_type = 'Trade';
    RETURN OLD;   
  END;
  $$;

CREATE TRIGGER deleteTradesGlEntriesTrigger 
  BEFORE DELETE ON trades
  FOR EACH ROW EXECUTE PROCEDURE deleteGlEntriesOfTrade();

Create a migration and use :)