27 cards

Writing raw SQL queries

If you really, really have a good reason to write raw SQL (generally a bad practice), make sure you use the right call.

Avoid ActiveRecord::Base.connection.execute in general, in particular because Octopus relies on this to determine which queries go to replicas. execute would always go to the master.

A number of other methods Archive are available: select_value, select_rows, of update being the most usual.


Find out branches containing a commit

If you have a commit and you want to see in what branches is is included, you have to write this:

git branch -r --contains [COMMIT-SHA]

-r is for remote


When you set date attributes, you should not pass times

As you know, time zones make stuff a bit more difficult but are necessary.

A time-zoned record is converted to UTC using to_s(:db) to be stored, and put back into the correct time zone when loaded. So when you are not on UTC, the following will happen:

>> Time.current
=> Fri, 15 Mar 2013 11:56:03 CET +01:00
>> Time.current.to_s(:db)
=> "2013-03-15 10:56:03" # This is now UTC

That will blow up in your face when you sen...

Linked contentRepeats

Add indexes on foreign keys when you create a migration (with foreign key)

Whenever you make a migration to add a foreign key, you should also add an index for it

  def self.up
    add_column :comments, :user_id, :integer
    add_index :comments, :user_id

Rebase your feature branches

Regularly, but at least before merging your feature branches, rebase them to get rid of "fix typo" and "wip" commits.

Getting rid of unnecessary commits

Let's say you do a git rebase -i HEAD~~~~ and have this commit history:

pick 1d1e1f My Feature
pick 2d2e2f My Feature - wip
pick 3d3e3f My Feature - fix typo
pick 4d4e4f My Other feature

Change it to use fixup for those commits that should be merged into the one before ...


Keeping your specs DRY

I often see long before blocks with lots of should_receive ... and_return inside.

Remember that before blocks are about setting up the "stage" (the context of your test), not declaring your expectations!
Also, they get run for every spec (every it block).

So :

  • convert your should_receives to stub calls in before blocks;
  • have one or more it blocks with should_receive, if you actually care that the calls are made (watch out not to expect calls that are just an implementation details, only things that you need to see ca...

Database: Scopes, migrations, and indices

Wether you modify an existing named scope or add a new one, or when you write a new query, make sure you have the proper indices.

This particularly applies if you're going to run non-trivial queries of course (admin backends, analytics, etc).

Compound indices

A chain of scopes results in (usually) one query. You should take into account all attributes (columns) that are used in :conditions, :join, :group, :having, and :order, as all those result in filtering and sorting–slow operations without indices.

Take the list of all ...

Linked contentRepeats

Respect time zones: Use Time.current and Time.zone.parse

Reading the current time

Don't use Time.now as it's broken when using time zones. \
Instead, use Time.current, DateTime.current or Date.current (the latter actually not being different, but just use it for good measure).

Parsing strings

Don't use Time.parse as it only gives you a Time object.
Use Time.zone.parse instead for a TimeWithZone.


How to run long scripts on production/staging server

In a nutshell, use screen

Sometimes we are concerned that if our connection gets closed, the process we are running will close too.

The processes or login sessions you establish through screen don't go away. You can resume your screen sessions.


  1. run screen command
    or you can give that screen a name (will help afterwards)
    screen -S some_name

  2. run your time consuming command
    script/runner path_to_some_long_script.rb

  3. detatch from your screen with the following commands

  • `Crt...

Odd referrer issue

The request referrer is the URL you come from. It's set by the browser when you click a link (all browsers) and in Javascript click events too (all but the Internet Explorer family).

If you click a link on a page:

request.referer == request.referrer == request.env['HTTP_REFERER']

So far so good. But if you write the URL straight into the browser:

request.referer == request.env['HTTP_REFERER'] == nil


request.referrer == '/'

instead of nil.

This seems to happen in our current version of Rails, although not in Rails >= 3.x...

Linked content

Bundle install in parallel

Gave a shot to the new Bundler 1.4.0RC1 during the weekend and found out it now supports gem installation in parallel. To invoke you need to pass --jobs parameter with number of threads you want it to run – for me the best performance was achieved by specifying the number physical CPU cores.

I've tested on the AppFab Archive app. In my case (CPU with 2-core i7 with HT) the speedup was 50%. I've also tried with a number greater than the number of physical cores but the performance was 15%-20% worse.

Bundler 1.3...

Avoid png file uploads with RSpec + Paperclip + Imagemagick

File uploads with .png are +10 times slower than using .jpeg or .gif.

# Bad
post :create, {
  :property_id => property.id,
  :photo => {
    :image => File.open("#{Rails.root}/public/images/foo.png")

# Good
post :create, {
  :property_id => property.id,
  :photo => {
    :image => File.open("#{Rails.root}/public/images/foo.jpeg")

jQuery ajax success/done will not run callbacks if request is json but the response is empty (typical 200)

When using

var onDone = function() { ... }
var onFail = function() { ... }
var params = { ... }
var url = ...

  type:  'put',
  url:  url,
  contentType: 'application/json; charset=utf-8',
  data:  JSON.stringify(params),

Always make sure your rails controller returns something:

if @property.update_attributes(params[:property])
  render :json => { :ok => true }, :status => :ok
  render :json => { :ok => false }, :status => :unpro...

Error: unable to read font `/usr/local/share/ghostscript/fonts/n019003l.pfb' @ error/annotate.c/RenderFreetype/1123: `(null)'

This happens when your machine does not have ghostscript installed, to fix it simply do

brew install ghostscript

Ruby: Don't a add return in ensure

This method won't throw an error:

def a_method
  return :something

it will in fact return :something

So please proceed with care :)

If you GROUP BY, make sure you ORDER BY NULL

TL;DR: If using :group => :some_field you might want to :order => 'NULL'.

According to the man Archive

By default, MySQL sorts all GROUP BY col1, col2, ... queries as if you specified ORDER BY col1, col2, ... in the query as well. If you include an ORDER BY clause explicitly that contains the same column list, MySQL optimizes it away without any speed penalty, although the sorting still occurs. If a query includes GROUP BY but you want to avoid the overhead of sorting ...

DateTimes are Dates, beware


datetime = DateTime.now
date = datetime.to_date #or Date.today

will assert:

datetime.is_a? Date == true
datetime.is_a? DateTime == true
datetime.instance_of? Date == false
datetime.instance_of? DateTime == true

In case you have a table and a model like:

create_table :event do |t|
  t.date    :day
  t.string  :description
class Event < ActiveRecord::Base; end

And you say:

event = Event.new(:day => '2013-03-22')

Rails will convert the supplied value for day to the type of the database field,...

Profiling Ruby with ruby-prof

require 'ruby-prof' # you don't need this if you have ruby-prof in your Gemfile

You can set one of the things you want to measure by using (default is PROCESS_TIME most useful ones are PROCESS_TIME, MEMORY, CPU_TIME):
RubyProf.measure_mode = RubyProf::PROCESS_TIME
RubyProf.measure_mode = RubyProf::WALL_TIME
RubyProf.measure_mode = RubyProf::CPU_TIME
RubyProf.measure_mode = RubyProf::ALLOCATIONS
RubyProf.measure_mode = RubyProf::MEMORY
RubyProf.measure_mode = RubyProf::GC_RUNS
RubyProf.measure_mode = ...

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