edge_rider is Power tools for ActiveRecord relations (scopes). Please note that some of the functions edge_rider provides have native implementations in newer rails versions.

Useful in applications

Relation#traverse_association(*names)

Edge Rider gives your relations a method #traverse_association which returns a new relation by "pivoting" around a named association. You can traverse multiple associations in a single call. E.g. to turn a relation of posts into a relation of all posts o...

Directly from the MySql docs:

There are three likely causes for this error message.

Usually it indicates network connectivity trouble and you should check the condition of your network if this error occurs frequently. If the error message includes during query, this is probably the case you are experiencing.

Sometimes the during query form happens when millions of rows are being sent as part of one or more queries. If you know that this is happening, you should try increasing net_read_timeout from its default of 30 seconds to 60 s...

When connecting to multiple (i.e. > 4) servers to dive into logfiles or do security updates, terminator is what you want.
There are several keyboard shortcuts available:

• Ctrl-Shift-E: Split the view vertically.
• Ctrl-Shift-O: Split the view horizontally.
• Ctrl-Shift-P: Focus be active on the previous view.
• Ctrl-Shift-N: Focus be active on the next view.
• Ctrl-Shift-W: Close the view where the focus is on.
• Ctrl-Shift-Q: Exit terminator.
• Ctrl-Shift-X: Enlarge active window...

As you know, assignable_values does not invalidate a record even when an attribute value becomes unassignable. See this example about songs:

class Song < ActiveRecord::Base
  belongs_to :artist
  belongs_to :record_label

  assignable_values_for :artist do
    record_label.artists
  end
end

We'll create two record labels with one artist each and create a song for one artist. When we change the song's record label, its artist is still valid.

makandra = RecordLabel.create! name: 'makandra records'
dominik...

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 on:

'ä'.unpack('U*...

jQuery plugin that makes it easy to dynamically add and remove records when using ActiveRecord's nested attributes.

ActiveRecord caches results of SQL queries. If you want to discard the cached results for one model, you can call MyModel.connection.clear_query_cache.

Edge Rider gives your relations a method #origin_class that returns the class the relation is based on.
This is useful e.g. to perform unscoped record look-up.

Post.recent.origin_class
# => Post

Note that #origin_class it roughly equivalent to the blockless form of #unscoped from Rails 3.2+, but it works consistently across all Rails versions. #unscoped does not exist for Rails 2 and is broken in Rails 3.0.

Declare an enum attribute where the values map to integers in the database, but can be queried by name.

In a nutshell:

• Splitting a long method into sub methods is easier in instances since it is in classes. Since you must not save state in a class, you need to pass around context as a long chain of parameters again and again.
• If your public API has a single entry point, you can still have a class-level method that takes care of constructing the instance etc. So it's all win.

When you, as a developer, look at the choices used to build a particular application, you’re blown away at the poor decisions made at every turn. “Why, oh why, is this built with Rails when Node.js would be so much better?” or “how could the previous developer not have forseen that the database would need referential integrity when they chose MongoDB?” But what you may not realize is that you are seeing the application as it exists today. When the previous developer (or team) had to develop it, they had to deal with a LOT of unknowns. They...

Local testing allows you to test your private and internal servers using the BrowserStack cloud, which has support for firewalls, proxies and Active Directory.

By default, Rails' validates_uniqueness_of does not consider "username" and "USERNAME" to be a collision. If you use MySQL this will lead to issues, since string comparisons are case-insensitive in MySQL.

(If you use PostgreSQL, read this instead.)

Say you have a user model

class User < ActiveRecord::Base
  validates_uniqueness_of :name
end

with a unique index in the database.

If you try to create the users "user" and "USER", this will not trigger a validation error, but may fail with an SQL error due ...

Put the attached file to config/initalizers to ignore some fields for rejecting nested records (e.g. hidden input fields).

class Post < ActiveRecord::Base
  
  has_many :comments
  accepts_nested_attributes_for :comments, :reject_if => all_blank_except(:position, :other_nested_attrs)

end

Just found out about a great feature in Rails that seems to be around since Rails 2. Start a console with the --sandbox (or -s) parameter:

rails console --sandbox

All changes you make to the database will be rolled back on exit.

Warning

Changes beyond the database (deleting files, sending emails, etc) cannot be rolled back!

Like in any language, a FLOAT will eventually corrupt data due to rounding errors.

Please use DECIMAL, which has well-defined behavior for rounding and range overflows.

Arel is a library that was introduced in Rails 3 for use in constructing SQL queries. Every time you pass a hash to where, it goes through Arel eventually. Rails exposes this with a public API that we can hook into when we need to build a more complex query.

If you get this error while trying to resize an openstack instance:

# nova resize fooinstance 16 --poll

==> /var/log/nova/nova-scheduler.log <==
2014-01-30 17:40:34 WARNING nova.scheduler.manager [req-aaaaaaa-bbbb-cccc-dddd-1ed34b64adef bajd7394hftgs71dba31d642342effa0f bfe2djhg6538sg384jgb82ks070ce0b] Failed to schedule_prep_resize: No valid host was found. 
2014-01-30 17:40:34 WARNING nova.scheduler.manager [req-aaaaaaa-bbbb-cccc-dddd-1ed34b64adef bajd7394hftgs71dba31d642342effa0f bfe2djhg6538sg384jgb82ks070ce0b] Setting ...

If your terminal has many tabs, you'll want to keep them organized. To change their title from the prompt, run this function:

function tab_title {
  if [ -z "$1" ]
  then
    title=${PWD##*/} # current directory
  else
    title=$1 # first param
  fi
  echo -n -e "\033]0;$title\007"
}

Put it into your ~/.bashrc to have it always available. Adjust to your needs.

Usage

$> tab_title
# title set to the current directory's name
$> tab_title new_title
# title set to "new_title"

Auto-setting the title
=================...

I had a huge MySQL dump that took forever (as in: days) to import, while I actually just wanted to have the full database structure with some data to use on my development machine.

After trying several suggestions on how to speed up slow MySQL dump imports (which did not result in any significant improvement), I chose to import just some rows per table to suffice my needs. Since editing the file was not an option, I used a short Ruby script to manage that.

Here is how:

pv huge.dump | ruby -e 'ARGF.each_line { |l| m = l.match(/^INSERT ...

You might sometimes use self to capture the context of this before it is destroyed by some function.

Unfortunately self is also an alias for window, the global top-level object. Save your future self some headaches and use another name like me instead (Coffeescript chose to use _this).

We have released Modularity 2. It has many incompatible changes. See below for a script to migrate your applications automatically.

There is no does method anymore

We now use traits with the vanilla include method:

class Article < ActiveRecord::Base
  include DoesTrashable
end

When your trait has parameters, use square brackets:

class Article < ActiveRecord::Base
  include DoesStripFields[:name, :brand]
end

Note how you ...

When you do something like this in your code:

def var_value
  @var ||= some_expensive_calculation
end

Be aware that it will run some_expensive_calculation every time you call var_value if some_expensive_calculation returns nil.

This illustrates the problem:

def some_expensive_calculation
  puts "i am off shopping bits!"
  @some_expensive_calculations_result
end

When you set @some_expensive_calculations_result to nil, ||= runs some_expensive_calculation every time....

TLDR: This card explains which threads and processes interact with each other when you run a Selenium test with Capybara. This will help you understand "impossible" behavior of your tests.

When you run a Rack::Test (non-Javascript) test with Capybara, there is a single process in play. It runs both your test script and the server responding to the user interactions scripted by your test.

A Selenium (Javascript) test has a lot more moving parts:

1. One process runs your test script. This is the process you...