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Drawing diagrams with draw.io

draw.io is a web application that lets you draw flow charts and other diagrams. It works much nicer than office suite tools like LibreOffice Draw.

Its UI is easy to use: Simply drag and drop shapes or arrows from the left-hand side onto your sheet. Drag start/end of arrows to shapes to automatically connect them. You can add text to shapes by selecting them and typing. To add colors, select a shape and use the right-hand panel.

While you can, you don't need to store your charts online. "Offline" storage can be files…

Repeats

Ruby constant lookup: The good, the bad and the ugly

In Ruby, classes and modules are called constants. This card explains how Ruby resolves the meaning of a constant.

The good

E. g. in the following example, Array could mean either Foo::Array or simply Array:

class Foo
  def list
    Array.new
  end
end

What Ruby does here is to see if the name Array makes sense inside of Foo::, and if that fails, resolves it to ::Array (without a namespace).

The bad

You might be surprised that these are all valid ways to reference Ruby's String class:

Upgrading a Rails app to Cucumber 3

Upgrade gems

You need to update a lof gems. Make sure you don't have any version constraints in your Gemfile or your bundle update won't do anything!

Upgrade cucumber_priority:

bundle update cucumber_priority

Upgrade spreewald:

bundle update spreewald

Upgrade cucumber_factory:

bundle update cucumber_factory

Upgrade parallel_tests:

bundle update parallel_tests

Even on the latest version, parallel_tests will print some deprecation warnings due to using an older formatter A…

How to fix HTML elements being cut off when printing

When you print (or print preview) and elements are cut off (e.g. after 1st page, or "randomly") you should check your CSS rules for these:

  • Is there an element with "display: inline-block" that surrounds your content? Make sure it has "display: block" for printing.
    This primarily affects Firefox and Internet Explorer. Chrome seems to be able to handle inline-block elements in most cases.

  • Does the element itself, or a container, define "overflow: hidden"? Use "overflow: auto" (or maybe "overflow: visible") instead.

  • Is th…

Repeats

Running Rspec examples by name, or: Running a single shared example

When an Rspec example fails, I usually investigate by running that example again using rspec <file:line>. However, this does not work with shared examples, since Rspec doesn't know in which context the shared example should be run.

But there is a different way: You can run the shared example using the -e, --example option. It takes a string value and runs all scenarios containing that substring in their full description.

This allows you to run a single uniquely named example, all examples with
similar names, all the examples in a u…

Custom Ruby method Enumerable#count_by (use for quick statistics)

I frequently find myself needing a combination of group_by, count and sort for quick statistics. Here's a method on Enumerable that combines the three:

module Enumerable
  def count_by(&block)
    list = group_by(&block)
      .map{ |key, items| [key, items.count] }
      .sort_by(&:last)
      
    Hash[list]
  end
end

The new method returns a Hash of key => count pairs.

Usage examples

Number of email addresses by domain:

```
> User.all.count_by { |user| user.email.sub /^.*@/, '' }
=> { "sina.cn"=>2, …, "yahoo.c…

An incomplete guide to migrate a Rails application from paperclip to carrierwave

In this example we assume that not only the storage gem changes but also the file structure on disc.

A general approach

Part A: Create a commit which includes a script that allows you to copy the existing file to the new file structure.

Part B: Create a commit which removes all paperclip logic and replace it with the same code you used in the first commit

Part A

Here are some implementation details you might want to reuse:

  • Use the existing models to read the files from
  • Use your own carrierwave models to write t…
Repeats

Printing background color of elements

Browsers' printing methods usually don't print background colors. In most cases this is the desired behavior, because you don't want to spent tons of ink printing the background of a web page. But in some cases you want to print the background color of elements, e.g. bars of a chart. For those elements you need to set the following css styles:

Chrome and Safari:

-webkit-print-color-adjust: exact;

Firefox:

color-adjust: exact;

Chrome: Making high-resolution website screenshots without add-ons

If you want to make a screenshot of a website that works well in print or on a high-DPI screen (like Apple Retina displays), here is how you can capture a high-resolution screenshot.

You can do this without an addon:

  • Open the website
  • If you have multiple monitoros:
    • Resize the Chrome window so it covers multiple monitors (in Linux you can hold ALT and resize by dragging with the right mouse button)
    • Zoom into the page using CTRL + and CTRL - so it covers most of the window area. Leave generous padding on the left and right so…
Repeats

Cucumber: Identifying slow steps that drag down your test speed

In most projects I know, Cucumber test suite speed is not an issue. Of course, running 350 features takes its time, but still each test for itself is reasonably fast. There is nothing you can do to fundamentally speed up such a test (of course, you should be using parallel_tests).

However, in projects that go beyond clicking around in a web GUI and checking results, there might be various measures to speed things up. Katapult tests for example could be sped up more than 4 times by re…

How to fix broken font collisions in wkhtmltopdf

If you are using PDFKit / wkhtmltopdf, you might as well want to use custom fonts in your stylesheets. Usually this should not be a problem, but at times they include misleading Meta-information that leads to a strange error in the PDF.

The setup

  • The designer gave you two fonts named something like BrandonText-Regular and BrandonText-Bold. (With flawed Meta-information)
  • You have a HTML string to be rendered by PDFKit
  • For demonstration purposes, this strin…

Quickly printing data in columns on your Ruby console

Dump this method into your Ruby console to quickly print data in columns. This is helpful for e.g. comparing attributes of a set of Rails records.

def tp(objects, *method_names)
  terminal_width = `tput cols`.to_i
  cols = objects.count + 1 # Label column
  col_width = (terminal_width / cols) - 1 # Column spacing

  Array(method_names).map do |method_name|
    cells = objects.map{ |o| o.send(method_name).inspect }
    cells.unshift(method_name)

    puts cells.map{ |cell| cell.to_s.ljust(col_width) }.join ' '
  end

  nil
end

Usag…

Repeats

Debugging cucumber feature with javascript + firefox vnc

TL;DR Debugging problems with javascript errors in cucumber tests is sometimes easier in the browser. Run the test, stop at the problematic point (with Then pause from Spreewald 1.7+) and open VNC for Firefox.

Features:

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…

Form letters with LibreOffice Writer

This is painful. Consider using Microsoft Office or switching careers. If you need to write < 20 letters consider doing it manually.

So you didn't listen and here it comes:

  1. Ignore the Mail Merge Wizard. It will crash or destroy your document.
  2. Export your addresses, recipient names, etc. as a .ods spreadsheet (.xls, .xlsx, .ods). Use any columns that work for you, but be consistent. I like to use one column for the address, one column for the salutation line.
  3. Import the spreadsheet as an address book source: *Tools => Add…
Repeats

Async control flow in JavaScript: Promises, Microtasks, async/await

Slides for Henning's talk on Sep 21st 2017.


Understanding sync vs. async control flow

Talking to synchronous (or "blocking") API

print('script start')
html = http_get('/foo')
print(html)
print('script end')

Script outputs 'script start', (long delay), '<html>...</html>', 'script end'.

Talking to asynchronous (or "evented") API

print('script start')
http_get('foo', done: function(html) {
  print(html)
}
print('script end')

Script outputs `'script st…

Repeats

PSA: Umlauts are not always what they seem to be

When you have a string containing umlauts which don't behave as expected (are not matched with a regexp, can't be found with an SQL query, do not print correctly on LaTeX documents, etc), you may be encountering umlauts which are not actually umlaut characters.

They look, depending on the font, like their "real" umlaut counterpart:

  • ä ↔ ä
  • ö ↔ ö
  • ü ↔ ü

However, they are not the same:

>> 'ä' == 'ä'
=> false
>> 'ä'.size
=> 1
>> 'ä'.size
=> 2

Looking at how those strings are constructed reveals what is going…

Howto: Require gem that is not in Gemfile

Example: Require awesome_print in the console while it is not in Gemfile or .gemspec.

require 'awesome_print' => LoadError: cannot load such file -- awesome_print

gem install 'awesome_print'

$: << `/home/xxx/.rvm/rubies/ruby-x.x.x/lib/ruby/x.x.x/gems/awesome_print-x.x.x/lib`
require 'awesome_print' => true

Note: To find out the path quickly just look at $: to get the base path of your ruby dir and then append the gem with version of the output of gem install.


Alternatives:
Adding the gem to the developme…

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