HOWTOs for Ruby on Rails and JavaScript - makandra dev

How to use pessimistic row locks with ActiveRecord

When requests arrive at the application servers simultaneously, weird things can happen. Sometimes, this can also happen if a user double-clicks on a button, for example.

This often leads to problems, as two object instances are modified in parallel maybe by different code and one of the requests writes the results to the database.

In case you want to make sure that only one of the requests "wins", i.e. one of the requests is fully executed and completed while the other one at least has to wait for the first request to be completed, you ha...

Detect the current Rails environment from JavaScript or CSS

Detecting if a Javascript is running under Selenium WebDriver is super-painful. It's much easier to detect the current Rails environment instead.

You might be better of checking against the name of the current Rails environment. To do this, store the environment name in a data-environment of your <html>. E.g., in your application layout:

<html data-environment=<%= Rails.env %>>

Now you can say in a pi...

In MySQL, a zero number equals any string

In MySQL comparing zero to a string 0 = "any string" is always true!

So when you want to compare a string with a value of an integer column, you have to cast your integer value into a string like follows:

SELECT * from posts WHERE CAST(posts.comments_count AS CHAR) = '200'

Of course this is usually not what you want to use for selecting your data as this might cause some expensive database operations. No indexes can be used and a full table scan will always be triggered.

If possible, cast the compared value in your application to...

A community-curated list of flexbox issues and cross-browser workarounds for them

This repository is a community-curated list of flexbox issues and cross-browser workarounds for them. The goal is that if you're building a website using flexbox and something isn't working as you'd expect, you can find the solution here.

As the spec continues to evolve and vendors nail down their implementations, this repo will be updated with newly discovered issues and remove old issues as they're fixed or become obsolete. If you discover a bug that's not listed here, please report it so everyone else can benefit.

How to fix "Exit with code 1 due to network error: ProtocolUnknownError" with wkhtmltopdf

New versions of wkhtmltopdf dissallow file:// URLs by default. You can allow them by passing --enable-local-file-access.

If you are using PDFKit, set the option

PDFKit.configure do |config|
  config.default_options = {
    enable_local_file_access: true,
  }
end

This will be necessary in many setups to allow wkhtmltopdf to fetch assets (such as stylesheets) from the filesystem.

Note on security

Allowing this poses some risk when you render user input, since it might be feasible to include data from the local filesyste...

RubyMine: Find and Replace with Regex (Capture Groups and Backreferences)

tl;dr

In RubyMine you can use find and replace with capture groups (.*?) and backreferences $1 (if you have several groups: $[Capture-Group ID]).
Named captures (?<text>.*) are also supported.

Examples

Replace double quotes with single quotes

If you want to replace double quotes with single quotes, replacing every " with a ' is prone to errors. Regular expressions can help you out here.

Open find and replace
Activate the regex mode (click on the .* icon next to the "find" field).
Fill in f...

find_and_replace_2.png find_and_replace_3.png find_and_replace_4.png find_and_replace.png

SEO: The subtle differences of robots.txt disallow vs meta robots no-index

The robots.txt file and <meta name="robots"> HTML tag can be used to control the behavior of search engine crawlers. Both have different effects.

robots.txt

Marking a URL path as "disallowed" in robots.txt tells crawlers to not access that path.

robots.txt is not a guarantee for exclusion from search engine results.

A "disallowed" URL might be known from an external link, and can still be displayed for a matching search.
Example: even if /admin is disallowed in robots.txt, `/admin/som...

workingdraft.de

Do not use "flex: 1" or "flex-basis: 0" inside "flex-direction: column" when you need to support IE11

Flexbox is awesome. Most of it even works in IE11, but flex: 1 won't work reliably in Internet Explorer.
This it because implicitly sets flex-basis: 0 which IE fails to support properly.

Example

Consider the following HTML and CSS.

<div class="container">
  <div class="child">
    foo
  </div>
  <div class="bar">
    bar
  </div>
</div>

.container {
  display: flex;
  flex-direction: column;
}

.child {
  flex: 1;
}

See it in action at Plunker.

Background

...

Project management best practices: Standup

If the project team consists of at least 2 members, do a daily standup. It should not take much longer than 15 minutes.

Format

Tell everyone else

what you did yesterday
what you intend to do today
where you might need help or other input
if there are new developments everyone needs to know about

A "still working on X, will probably be done today" is totally fine. No need to tell a long story.

If you are out of work, find a new story with the others.

If there are new stories in the backlog, look at them and

make sure ev...

Prefer using Dir.mktmpdir when dealing with temporary directories in Ruby

Ruby's standard library includes a class for creating temporary directories. Similar to Tempfile it creates a unique directory name.

Note:

You need to use a block or take care of the cleanup manually
You can create a prefix and suffix e.g. Dir.mktmpdir(['foo', 'bar']) => /tmp/foo20220912-14561-3g93n1bar
You can choose a different base directory than Dir.tmpdir e.g. `Dir.mktmpdir('foo', Rails.root.join('tmp')) => /home/user/rails_example/tmp/foo20220912-14...

How to get the git history of a file that does not exist anymore

If you want to see the git history of a project file, that doesn't exist anymore, the normal git log <path_to_file> won't work. You have to add certain flags to make it work:

git log --all --full-history -- <path_to_file>

Rails: Comparison of Dates - before? and after?

tl;dr

Since Rails 6+ you can use before? and after? to check if a date/time is before or after another date/time.

Example

christmas = Date.parse('24.12.2022')
date_of_buying_a_gift = Date.parse('12.12.2022')

date_of_buying_a_gift.before?(christmas)
# => true
# Now you are well prepared for Christmas!! ;)

date_of_buying_a_gift = Date.parse('26.12.2022')

date_of_buying_a_gift.after?(christmas)
# => true
# Now you are too late for christmas! :(

Hint

If you want to check if a date/time is between to ot...

Statistics and Reports on Web Performance Optimization

Case studies and experiments demonstrating the impact of web performance optimization (WPO) on user experience and business metrics.

Careful: `fresh_when last_modified: ...` without an object does not generate an E-Tag

To allow HTTP 304 responses, Rails offers the fresh_when method for controllers.

The most common way is to pass an ActiveRecord instance or scope, and fresh_when will set fitting E-Tag and Last-Modified headers for you. For scopes, an extra query is sent to the database.

fresh_when @users

If you do not want that magic to happen, e.g. because your scope is expens...

Ruby and Rails: Debugging a Memory Leak

A memory leak is an unintentional, uncontrolled, and unending increase in memory usage. No matter how small, eventually, a leak will cause your process to run out of memory and crash.

If you have learned about a memory leak, looking at the number of Ruby objects by type can help you track it down:

> pp ObjectSpace.count_objects
{:TOTAL=>77855,
 :FREE=>4526,
 :T_OBJECT=>373,
 :T_CLASS=>708,
 :T_MODULE=>44,
 :T_FLOAT=>4,
 :T_STRING=>65685,
 :T_REGEXP=>137,
 :T_ARRAY=>984,
 :T_HASH=>87,
 :T_STRUCT=>12,
 :T_BIGNUM=>2,
 :T_FILE=>3,
 :T_D...

Rails: Custom validator for "only one of these" (XOR) presence validation

For Rails models where only one of multiple attributes may be filled out at the same time, there is no built-in validation.

I've seen different solutions in the wild, each with different downsides:

Private method referenced via validate: works, but is barely portable and clutters the model.
Multiple presence validations with "if other is blank" each: looks pretty, but is incorrect as it allows both values to be filled in; also the error messages for a blank record are misleading.

Here is a third option: Write a custom validator to ...

Converting SVG to other vector formats without Inkscape

If you need to convert an SVG source to PS or EPS, the most common suggestion on the interwebs is to use Inkscape from the commandline.
Inkscape is a fairly resource-heavy tool with lots of dependencies. A great alternative for converting is CairoSVG.

CairoSVG is available on most Linux distros through their package management systems, e.g. apt install cairosvg on Ubuntu.
It has few dependencies (most importantly Python 3 and some related packages, but really not much)...

Helper methods - RSpec Core

You can define methods in any example group using Ruby's def keyword or define_method method. These helper methods are exposed to examples in the group in which they are defined and groups nested within that group, but not parent or sibling groups.

How to bulk-unwatch many repositories on Github

To easily opt out of notifications for a large number of Github repositories, go to https://github.com/watching.

A simpler default controller implementation

Rails has always included a scaffold script that generates a default controller implementation for you. Unfortunately that generated controller is unnecessarily verbose.

When we take over Rails projects from other teams, we often find that controllers are the unloved child, where annoying glue code has been paved over and over again, negotiating between request and model using implicit and convoluted protocols.

We prefer a different approach. We believe that among all the classes in a Rails project, controllers are some of the hardest to...

Controlling how your website appears on social media feeds

When a user shares your content, a snippet with title, image, link and description appears in her timeline. By default social networks will use the window title, the first image, the current URL and some random text snippet for this purpose. This is often not what you want.

Luckily Facebook, Twitter, etc. lets you control how your content appears in the activity streams. They even have agreed on a common format to do this: OpenGraph <meta> tags that go into your HTML's <head>:

<meta property="og:url" content="http://start.m...

Defining new elements for your HTML document

Browsers come with a set of built-in elements like <p> or <input>. When we need a new component not covered by that, we often build it from <div> and <span> tags. An alternative is to introduce a new element, like <my-element>.

When a browser encounters an unknown element like <my-element>, the browser will proceed to render <my-element>'s children. The visual rendering of your page will not be affected.

If you care about their HTML being valid, your new element should contain a dash character (-) to mark it as a *custom el...

Updated: Git: removing feature branch on merge

Resolve @{-1} to actual branch name. (Happens when merging "-".)

makandracards.com

Creating a Rails application in a single file

Greg Molnar has written a neat article about creating a single-file Rails app.
This is not meant for production use but can be useful to try things out, e.g. when hunting down a bug or embedding a Rails app into the tests of a gem.

What you do is basically:

Put everything (gems, application config, database migrations, models, controllers) into a single .ru file, like app.ru.
Run it via rackup app.ru. (Hint: if your file is called config.ru, you can just run `rac...