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Rails asset pipeline: Why things break in production and what precompilation does to your assets

When you work with a Rails 3.1+ application, you will be working with the asset pipeline. The asset pipeline is awesome until you deploy. Then it will be less so if you haven't done everything as the pipeline expected it from you.

The problem

When using the asset pipeline your assets (images, javascripts, stylesheets, fonts) live in folders inside app:

app/assets/fonts
app/assets/images
app/assets/javascripts
app/assets/stylesheets

With the asset p…

ActionMailer: send mail from console

If your rails application is unable to send mails, it might be useful to debug your settings using the rails console. Here is a snippet that shows the current settings and lets you send a test mail directly from the console:

```ruby
m = ActionMailer::Base.new

check settings:

m.delivery_method # -> :smtp
m.smtp_settings # -> { address: "localhost", port: 25, domain: "localhost.localdomain", user_name: nil, password: nil, authentication: nil, enable_starttls_auto: true }

send mail:

m.mail(from: 'sender@example.com', to: 'recipient@examp…

Repeats

Redirecting responses for PATCH or DELETE will not redirect with GET

Redirect responses to PATCH and DELETE requests will be followed with PATCH or DELETE. Redirect responses to GET and POST will be followed with a GET.
The Rails form_for helper will use a workaround to send POST requests with a _method param to avoid this issue for PATCH/DELETE.

If you make requests yourself, watch out for the following behavior.

When you make an AJAX request PATCH /foo and the /foo action redirects to /bar, browsers will request PATCH /bar. You probably expected the second request to be…

Repeats

Don't compare datetimes with date ranges in MySQL

When selecting records in a date range, take care not to do it like this:

start_date = Date.parse('2007-05-01')
end_date = Date.parse('2007-05-31')
LogItem.where(:created_at => start_date .. end_date)

The problem is that created_at is a datetime (or Time in Ruby), while start_date and end_date are simple dates. In order to make sense of your query, MySQL will cast your dates to datetimes where the time component is 00:00:00. Because of this the query above will lose records created from 2007-05-31 00:00:01 t…

Repeats

Webpacker: Configuring browser compatibility

Webpacker uses Babel and Webpack to transpile modern JavaScript down to EcmaScript 5. Depending on what browser a project needs to support, the final Webpack output needs to be different. E.g. when we need to support IE11 we can rely on fewer JavaScript features. Hence our our output will be more verbose than when we only need support modern browsers.

Rails 5.1+ projects often use Webpacker to preconfigure the Webpack pipeline for us. The default configuration works something like this:

  1. Webpack chec…
Repeats

Carrierwave: Built-in RSpec matchers

CarrierWave comes with some RSpec matchers which will make testing more comfortable. Let's say you have an Uploader like this:

class MyUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick

  # Create different versions of your uploaded files:
  version :small do
    process resize_to_fill: [100, 100]
  end
  
  version :medium do
    process resize_to_fit: [200, nil]
  end
  
  version :large do
    process resize_to_limit: [400, 400]
  end

end

Imagine you have a class Movie with an attribute poster. In …

Repeats

How to create giant memory leaks in AngularJS

This guide shows how to create an AngularJS application that consumes more and more memory until, eventually, the browser process crashes on your users.

Although this guide has been written for Angular 1 originally, most of the advice is relevant for all client-side JavaScript code.

How to observe memory consumption

To inspect the amount of memory consumed by your Javascripts in Chrome:

  • Open an incognito window
  • Open the page you want to inspect
  • Press Shift + ESC to see a list of Chrome processes…
Repeats

When you want to format only line breaks, you probably do not want simple_format

For outputting a given String in HTML, you mostly want to replace line breaks with <br> or <p> tags.
You can use simple_format, but it has side effects like keeping some HTML.

If you only care about line breaks, you might be better off using a small, specialized helper method:

def format_linebreaks(text)
  safe_text = h(text)
  paragraphs = split_paragraphs(safe_text).map(&:html_safe)

  html = ''.html_safe
  paragraphs.each do |paragraph|
    html << content_tag(:p, paragraph)
  end    ...
Repeats

Fix PNG colors in IE, old Safaris and new Firefoxes

Some browsers render PNG images with color profiles and other shenanigans, some don't. Remove some PNG chunks to render colors uniformly.

Geordi brings a command png-optimize which conveniently optimizes your PNGs for the web. See Github for a description

  • Single file and batch optimization is supported
  • png-optimize will overwrite the original files

Without Geordi

Linux:
sudo apt-get install pngcrush
  • Single file:

    pngcrush -rem...
    
External content

Persist Rails or IRB Console Command History After Exit

Create, or edit your ~/.irbrc file to include:

require 'irb/ext/save-history'
IRB.conf[:SAVE_HISTORY] = 2000
IRB.conf[:HISTORY_FILE] = "#{ENV['HOME']}/.irb-history"

Understanding IRB warning "can't alias ... from ..."

Sometimes, the IRB prints a warning during boot:

irb: warn: can't alias source from irb_source.

Explanation

During boot, the IRB creates many aliases to give the user quick access to irb functions like source-ing a file.

However, if IRB's context already responds to the alias it wants to create, it will no…

Bundler error: Downloading gem revealed dependencies not in the API

Recent Bundler (1.16.1) started complaining about missing dependencies in the Gemfile. This is due to a stricter handling of specifications (see attached link).

The error message looks like this:

Downloading example-gem-1.2.3 revealed dependencies not in the API or the lockfile (other-gem (< 3)).
Either installing with `--full-index` or running `bundle update example-gem` should fix the problem.

However, bundle install --full-index did not any better for me, and bundle update is not always a viable solution.

Easiest solut…

Repeats

Testing the spam score of an email

This site gives you some hints, how you can improve the overall rate of successful deliveries. The analyse covers both the email formatting and the server configuration.

spam-score.jpg

Repeats

Use find_in_batches or find_each to deal with many records efficiently

Occasionally you need to do something directly on the server – like having all records recalculate something that cannot be done in a migration because it takes a long time.

Let's say you do something like this:

Project.all.each(&:recalculate_statistics!)

Even though you may have been successful with this on your development machine or the staging server, keep in mind that production machines often hold a lot more records. Using all may just work, even with lots of records, but when you iterate over such records and fetch associati…

PostgreSQL: How to show table sizes

When you have a large PG database, you may want to find out which tables are consuming the most disk space.
You can easily check this using the following SQL statement from the PostgreSQL wiki.

SELECT nspname || '.' || relname AS "relation",
    pg_size_pretty(pg_total_relation_size(C.oid)) AS "total_size"
  FROM pg_class C
  LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
  WHERE nspname NOT IN ('pg_catalog', 'information_schema')
    AND C.relkind <> 'i'
    AND nspname !~ '^pg_toast'
  ORDER BY pg_tot...
Repeats

simple_format does not escape HTML tags

simple_format ignores Rails' XSS protection. Even when called with an unsafe string, HTML characters will not be escaped or stripped!

Instead simple_format has a whitelist of tags it allows. These are:

ActionView::Base.sanitized_allowed_tags
=> #<Set: {"small", "dfn", "sup", "sub", "pre", "blockquote", "ins", "ul", "var", "samp", "del", "h6", "h5", "h4", "h3", "h2", "h1", "span", "br", "hr", "em", "address", "img", "kbd", "tt", "a", "acronym", "ab...
Repeats

Event order when clicking on touch devices

Touch devices have their own set of events like touchstart or touchmove. Because mobile browsers should also work with with web applications that were build for mouse devices, touch devices also fire classic mouse events like mousedown or click.

When a user follows a link on a touch device, the following events will be fired in sequence:

  • touchstart
  • touchend
  • mousemove
  • mousedown
  • mouseup
  • click

Canceling the event sequence ——————-…

Repeats

You don't need each, collect or select in Coffeescript

Working with lists in Javascript is painful because the native Array class is so poorly designed.

One way to reduce the pain is to to use Underscore.js's functions like _.each, _.map or _.select, which unfortunately clutters your code with awkward calls to the _ helper.

Fortunately when you use CoffeeScript you don't need any of that. CoffeeScript has a very versatile for keyword that can do anything that each, collect or select can do. Enjoy!

each

```
f…

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