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Adam Lassek alassek

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View discriminable_model.rb
# Wouldn't it be great if you could have STI like functionality
# without needing to encode strings of class names in the database?
# Well today is your lucky day! Discriminable Model is here to help.
# Simply specify your models desired type column, and provide a block to
# do the discrimination. If you want the whole STI-esque shebang of properly
# typed finder methods you can supply an array of 'discriminate_types' that will
# be used to apply an appropriate type.
# class MyModel < ActiveRecord::Base
View fast_pluck.rb
# speed up pluck
class ActiveRecord::Relation
class RailsDateTimeDecoder < PG::SimpleDecoder
def decode(string, tuple=nil, field=nil)
if Rails.version >= "4.2.0"
@caster ||=

An ActiveRecord conundrum

I'm going to describe a weird problem I faced when using ActiveRecord today. To protect the innocent, I'm not going to talk about the app I'm actually working on but will instead discuss a hypothetical but isomorphic database design for a clone of the popular blogging platform Tumblr.

Tumblr lets you publish various different sorts of content. We might be tempted to shove all these types in a big STI table, but the types are all quite different from one another and so we give them their own tables.

rietta / plpgsql.rake
Last active August 8, 2020 15:05
Are you using PostgreSQL and don't want to make your app run as PostgreSQL super user, then add this custom rake task to your `lib/tasks` folder and be happy.
View plpgsql.rake
# PostgreSQL writes two optional commands to the database schema
# file, called db/structure.sql, that can only be run as a root
# database user. These are not needed actually, so comment them
# out automatically
# COMMENT ON EXTENSION plpgsql IS 'PL/pgSQL procedural language';
namespace :db do
ernie / delegate.rb
Last active May 31, 2016 10:39
An alternate take on the delegation class macro provided by ActiveSupport. Updated with Ruby 2.0's caller_locations.
View delegate.rb
#!/usr/bin/env ruby
class Module
def delegate(*args)
dest, prefix = _extract_valid_delegation_options(args.pop)
_define_delegators(caller_locations.first, prefix, dest, args)

Falsehoods programmers believe about prices

  1. You can store a price in a floating point variable.
  2. All currencies are subdivided in 1/100th units (like US dollar/cents, euro/eurocents etc.).
  3. All currencies are subdivided in decimal units (like dinar/fils)
  4. All currencies currently in circulation are subdivided in decimal units. (to exclude shillings, pennies) (counter-example: MGA)
  5. All currencies are subdivided. (counter-examples: KRW, COP, JPY... Or subdivisions can be deprecated.)
  6. Prices can't have more precision than the smaller sub-unit of the currency. (e.g. gas prices)
  7. For any currency you can have a price of 1. (ZWL)
  8. Every country has its own currency. (EUR is the best example, but also Franc CFA, etc.)
View associations.rb
# use inverse_of to 'just work'
class User < ActiveRecord::Base
has_many :contributions, inverse_of: :user
has_many :posts, through: :contributions
class Post < ActiveRecord::Base
has_many :contributions, inverse_of: :post
has_many :contributors, through: :contributions,
source: :user
carlzulauf / thin.rb
Last active December 17, 2015 01:19
Thin initd script. Spawns thin daemons from a config directory using a specific non-privileged user (`carl`).
View thin.rb
#!/usr/bin/env ruby
# thin init script
# install to /etc/init.d/thin
# crazy debian LSB header stuff
# Provides: thin
# Required-Start: $local_fs $remote_fs
# Required-Stop: $local_fs $remote_fs
dergachev /
Last active February 12, 2024 17:18
OS X Screencast to animated GIF

OS X Screencast to animated GIF

This gist shows how to create a GIF screencast using only free OS X tools: QuickTime, ffmpeg, and gifsicle.

Screencapture GIF


To capture the video (filesize: 19MB), using the free "QuickTime Player" application:

avdi / selective_method_import.rb
Created January 16, 2013 06:35
Playing around with selective method import in Ruby
View selective_method_import.rb
# Generate a module which imports a given subset of module methods
# into the including module or class.
def Methods(source_module, *method_names)
all_methods = source_module.instance_methods +
unwanted_methods = all_methods - method_names
import_module = source_module.clone
import_module.module_eval do
define_singleton_method(:to_s) do
"ImportedMethods(#{source_module}: #{method_names.join(', ')})"