Angular with haml: Dynamic html classes

A haml angular 1 template with

.thing(class="is-{{:: item.type }}")

will be compiled (by haml) to

<div class="is-{{:: item.type thing }}"></div>

which is not what you want! It will also crash in angular (unless thing is a valid variable in your angular directive) with Error: [$parse:syntax] Syntax Error: Token 'thing' is an unexpected token at column 11 of the expression [item.type thing]

Solution 1: Use ng-class instead of class

.thing(ng-class='"is-{{ item.type }}"')

**Solution 2: Don't let haml b…

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Understanding AngularJS service types

Angular comes with different types of services. Each one with its own use cases.

All of these services are singletons. You probably want to use Factory all the time.


  • is the parent of all other services (except constant)
  • can be configured using `app.config(function(Provider) { ...})
  • a little complex


  • simpler than Provider, but without configuration
  • definition: `app.factory('name', someFunction)
  • someFunction is called when the name service is instantiated and should return an object



Nested ActiveRecord transaction pitfalls

When working with custom transactions you may encounter unexpected behaviour if you try to roll back your changes.


Not all databases support nested transactions. Therefore, Rails will sometimes silently ignore a nested transaction and simply reuse the other transaction. However, a ActiveRecord::Rollback within the nested transaction will be caught by the block of the nested transaction, but will be ignored by the outer transaction, and not cause a roll back!
To avoid this unexpected behaviour, you have to explicitly tell rai…


How to emulate simple classes in JavaScript

Since ES6 classes still have limited browser support, one workaround to ensure encapsulation is the revealing module pattern.


Here is an example for a Ruby class that we want to translate into Javascript using the module pattern.

It's a simple class with one private function:

class Dog

def initiali…


AppArmor in Linux

This note is to remember that there is something called AppArmor that could cause weird errors ("File not found", "Can't open file or directory", …) after configuration changes, e.g. when changing MySQL's data directory.

Remember to have a look at AppArmor's daemon configuration (usually at /etc/apparmor.d/) if you change daemon configuration and run into errors such as the one above.

How to "git diff" with a graphical diff tool

If you are fine with the default console diff most of the time but only sometimes want to use an external tool for viewing a diff, you can use git difftool.

E.g. viewing git diff with meld:

git difftool --tool=meld

For each file in the diff you will be asked if you want to view it using meld.

Add monitoring for Sidekiq

In order to have monitoring for Sidekiq (like queue sizes, last run of Sidekiq) your application should have a monitoring route which returns a json looking like this:

"sidekiq": {
"totals": {
"failed": 343938,
"processed": 117649167
"recent_history": {
"failed": {
"2016-11-06": 1,
"2016-11-07": 46,
"2016-11-08": 0,
"2016-11-09": 0,
"2016-11-10": 0
"processed": {
"2016-11-06": 230653,
"2016-11-07": 230701,
"2016-11-08": 23…

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mceachen/closure_tree: Easily and efficiently make your ActiveRecord models support hierarchies

Closure_tree lets your ActiveRecord models act as nodes in a tree data structure.

This promises a few improvements over the battle-tested ancestry gem, such as:

  • Better performance (an issue because ancestry does full table scans with Regexps on the ancestry column)
  • Pre-ordered trees (painful to do with ancestry)
  • Holds a mutex during tree manipulations (an issue with ancestry, where concurrent updates can cause deadlocks and corrupt data).

It has…

External contentRepeats

The Easiest Way to Parse URLs with JavaScript

A very clever hack to parse a structured URL object is to create a <a> element and set its href to the URL you want to parse.

You can then query the <a> element for its components like schema, hostname, port, pathname, query, hash:

var parser = document.createElement('a');
parser.href = '';
parser.hostname; // => ''
parser.pathname; // => '/bar'

One advantage vs. calling new URL(...) is that it works with incomplete URLs. So if al…

How to inspect really large directories

When a directory has more than a few thousand entries, ls will start taking really long to list its content. Reason for this is that ls by default a) sorts the file names and b) prints them in columns. For both, it needs to know (thus load into memory) the whole list of files before it can start printing anything.

By disabling sorting and columns, you get a lean, superfast ls that prints "live" as it reads:

$> ls -f -1
External contentRepeats

Ruby: What extend and include do

All Rubyists should be familiar with the common definitions for include and extend. You include a module to add instance methods to a class and extend to add class methods. Unfortunately, this common definition isn’t entirely accurate. It fails to explain why we use instance.extend(Module) to add methods to an instance. Shouldn’t it be instance.include(Module)? To figure this out we’re going to start by discussing where methods are stored.

Further reading

After you understood include and extend you might want to look …

External contentRepeats

Github Cheat Sheet

All the hidden and not hidden features of Git and GitHub.


Protected and Private Methods in Ruby

In Ruby, the meaning of protected and private is different from other languages like Java. (They don't hide methods from inheriting classes.)


Private methods can only be called with implicit receiver. As soon as you specify a receiver, let it only be self, your call will be rejected.

class A
  def public_method
  def other_public_method
  def private_method
    "I'm private"

Rails: Talking to the database without instantiating ActiveRecord objects

Instantiating ActiveRecord objects comes expensive. To speed up things, you can choose a more direct way to talk to your database: the ActiveRecord::ConnectionAdapters::DatabaseStatements module.

Using the module and its methods is not suggested in the usual in-app workflow, as validations, callbacks, custom getters/setters etc. are ignored. However, for database-centered stuff like migrations, these fill the gap between writing pure SQL and full…

AngularJS: How to remove a watch

Sometimes you want Angular to watch an object only until a certain state is reached (e.g. an object appears in the scope).

Angular's $watch returns a method that you can call to remove that watch. For example:

unwatch = $scope.$watch 'user', (user) ->
  if user?
    ... # do something

That's it.


How to discard ActiveRecord's association cache

You know that ActiveRecord caches associations so they are not loaded twice for the same object. You also know that you can reload an association to make Rails load its data from the database again.

# discards cache and reloads and returns user.posts right away
# => [...]

If you want to discard the cache but not query the database (only the next time the association is accessed), you can use reset:

# discards cache, but does not load anything yet
# SQL query hap...

Repeatedly execute a bash command and observe its output

You can have a command repeatedly executed and the output displayed. This is useful e.g. for monitoring file system changes with ls, but has many more applications.
The update frequency is controlled by the -n argument (default: 2s), which is locale-specific; i.e. you might need to use a comma as delimiter.

  > watch -n 1.5 ls
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tesseract.js: Pure Javascript OCR for 62 Languages

This might be relevant for us since we're often managing customer documents in our apps.

I played around with the library and this is what I found:

  • A 200 DPI scan of an English letter (500 KB JPEG) was processed in ~6 seconds on my desktop PC. It does the heavy lifting in a Web worker so you're rendering thread isn't blocked.
  • It detected maybe 95% of the text flawlessly. It has difficulties with underlined text or tight table borders.
  • When you feed …
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