Bash: Build and execute command lines on the fly with "xargs"
xargs is a powerful bash tool that can take input from $STDIN and pass it to a given command. I.e. you can do the following:
$> cat tmp/parallel_cucumber_failures.log
features/authentication.feature:33
features/backend/pages.feature:5
features/backend/pages.feature:60
$> cat tmp/parallel_cucumber_failures.log | xargs geordi cucumber
# Running features
> Only: features/authentication.feature:33 features/backend/pages.feature:5 features/backend/pages.feature:60
...
A non-weird replacement for grouped_collection_select
Rails comes with grouped_collection_select that appears to be useful, but isn't.
As an alternative, consider the flat_grouped_collection_select found below. It takes a third argument that extracts the group from each element in the collection:
= form.flat_grouped_collection_select :user_id, users, :department, :id, :full_name
Here is the monkey-patch:
```
class ActionView::Helpers::FormBuilder
def flat_grouped_collection_select(fi…
How to create memory leaks in jQuery
jQuery doesn't store information about event listeners and data values with the element itself. This information is instead stored in the global $.cache object. Every time you add an event listener or data value to a jQuery object, $.cache gains another entry.
The only way that a $.cache entry gets deleted is when you call remove() on the element that put it there!
Since cache entries also have a pointer back to the element that spawned them, it is easy to create DOM elements that can never be garbage-collected.
Below are …
How to examine an unknown Ruby object
When debugging your application, you will come across objects created by some gem or framework. You don't have the source code at hand, still need to inspect this object. Here are some tools to do so:
Relevant methods
@object.methods - Object.instance_methods returns a list of methods excluding methods inherited from Object. This makes the methods list drastically more relevant. You can also try subtracting other base classes like ActiveRecord::Base.methods etc.
Filtering method list
@object.methods.grep /keyword/ comes…
CSS: Match against attribute values (or parts of them)
You probably know that you can use CSS selectors to match against elements and their attributes, such as:
a[title] { /* any <a> that has a "title" */ }
a[data-fancy="true"] { /* any <a> that has their "data-fancy" attribute set to "true" */ }
But there is more: You do not need to match against "full" attribute values but can match against parts of them.
They work in all somewhat modern browsers, and IE9 or later.
- Exact match (CSS2)
-
[foo="bar"](matches<div foo="bar" />, but not `<div…
8 steps for fixing other people's code
Guide how to make fixes in other people's GitHub repositories. It's basically "Open Source Development 101".
Way back in mid-2007, when Rails 1.2 was the new hotness and GitHub was still a year away from crawling out of the primordial internet soup, prolific open source contributor Dr Nic wrote an article titled “8 steps for fixing other people’s code”. (…)
Here in the fantastical future world of 2012, while we still don’t have hoverboards or household nuclear fusion, we do have some great tools that make fixing other people’s code…
Do not pass an empty array to ActiveRecord.where when using NOT IN
Be careful with the Active Record where method. When you accidentally pass an empty array to the where method using NOT IN, you probably will not get what you expected:
User.where("id NOT IN (?)", [])
=> SELECT `users`.* FROM `users` WHERE (id NOT IN (NULL))
Even though you might expect this to return all records, this actually results none.
Never use the expression id NOT IN (?) in any scope! See below some workarounds.
Rails < 4
Rails < 4 does not provide a pretty workaround.
```
ids = []
if ids.present?
Us…
Ruby: required keyword arguments in the pre-2.1 era
Starting with Ruby 2.0 you can define methods with keyword arguments.
In 2.1+ required keyword arguments can be defined by using a colon without default value:
def match(value, ignore:)
...
end
To accomplish something similar in ruby 1.8, use:
def match(value, options = {})
ignore = options.fetch(:ignore)
...
end
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.
user.posts.reload
# 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:
user.posts.reset
# discards cache, but does not load anything yet
user.posts
# SQL query hap...
Updated: Minor caveat for minified Font Awesome fonts with webpack
I noticed that changing the subset of used icons does not change the file name of the generate font, and will cause issues with browser caching.
I've added a workaround.