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Ruby Quicktips

Random Ruby and Rails tips.
This blog is dedicated to deliver short, interesting and practical tidbits of the Ruby language and Ruby on Rails framework. Read more...

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Aug 18 ’12

Quick Hash to a URL Query trick

Got a hash of values you want to convert into a url query string? Use the to_query method:

"" + { language: "ruby", status: "awesome" }.to_query
# => "" 

Want to do it in reverse? Use CGI.parse:

require 'cgi' # Only needed for IRB, Rails already has this loaded
CGI::parse "language=ruby&status=awesome"
# => {"language"=>["ruby"], "status"=>["awesome"]} 

Both methods support nested values.

This tip was submitted by Victor Solis.

10 notes 0 comments

Jul 22 ’12

Testing CSV file uploads

Let’s say you have a form like this for uploading a CSV file:

<%= form_tag csv_import_path, :multipart => true do %>
  <%= file_field_tag :file, :accept => "text/csv" %>
  <%= submit_tag "Upload" %>
<% end %>

And your controller action looks like this:

require 'csv'

def csv_import    
  file_data = params[:file].read
  csv_rows  = CSV.parse(file_data)

  csv_rows.each do |row|
    # do something with each row
  respond_to do |format|
    format.html { redirect_to your_path, :notice => "Successfully imported the CSV file." }

How would you test this functionality?

You can’t use fixture_file_upload and stick a sample file in test/fixtures/files/ (as often suggested - e.g. here on SO). That’s because CSV and YAML files will be imported as fixtures into the test database as soon as you run tests. E.g., this would not work:

def test_file_upload
  post :csv_import, :file => fixture_file_upload('files/new_users.csv','text/csv')

But what you can do is to use the Tempfile and Rack::Test::UploadFile classes and manually create a CSV file and supply this to the post (or put) method:

def test_should_successfully_import_csv
  csv_rows = <<-eos

  file ='new_users.csv')

  assert_difference "User.count", 3 do
    post :csv_import, :file =>, 'text/csv')

  assert_redirected_to your_path
  assert_equal "Successfully imported the CSV file.", flash[:notice]

4 notes 0 comments

May 3 ’12

Using ActiveRecord to query for times within a range

You can pass a range to query for records within that range:


Just discovered this, something I wish I knew a LONG time ago.

Album.where(:created_at =>

Which will generate the following SQL query (depending on the database):

SELECT "albums".* FROM "albums" WHERE ("albums"."created_at" BETWEEN '2012-04-28 11:10:22.780712' AND '2012-04-30 11:10:22.780907')

14 notes 0 comments (via hackerinspiration)

May 1 ’12

Try out your helpers in the Rails console

Ever wanted to try out any of Rails’ view helper methods in the console? Just include ActionView::Helpers after starting the Rails console:

include ActionView::Helpers
# => Object
text_field(:post, :title)
# => "<input id=\"post_title\" name=\"post[title]\" size=\"30\" type=\"text\" />"

2 notes 0 comments

Apr 19 ’12

Creating regular expressions with r{} literals

Creating a regular expression using the r{} literals can for example be helpful when matching URLs, because you don’t have to escape slashes:

url = ""

# /../ literals:
url.match /http:\/\/example\.com\//
# => #<MatchData "">

# %r{} literals:
url.match %r{http://example\.com/}
# => #<MatchData "">

4 notes 0 comments

Apr 17 ’12

Create a hash from an array with Hash[*arr]

The Hash::[] class method can be used in addition to the splat operator to create a hash from an array.

arr = [:a, 1, :b, 2]
# => {:a => 1, :b => 2}

6 notes 0 comments

Apr 12 ’12

Rails’ index_by: the easy way to convert an Array to a Hash

As Aditya Sanghi notes in "Quickly convert an Array to a Hash", a very quick way to convert an Array to a Hash, is to use Rails’ Enumerable#index_by:

Post.all.index_by { |post| }
# => { 1 => #<Post ...>, 2 => #<Post ...>, ... }

# => { "My first post" => #<Post ...>, "My second post" => #<Post ...>, ... }

6 notes 0 comments

Apr 11 ’12

Convert a number string in any base to a decimal number

As Brich Thompson notes in the comments on "Convert between number bases easily", you can also convert a number string in any base to a decimal number with the String#to_i method:

"21".to_i     #=> 21 
"21".to_i(8)  #=> 17
"21".to_i(16) #=> 33

4 notes 0 comments

Apr 4 ’12

Two Ruby tricks using method chaining and Procs

# => [2, 3, 4]

# Same outcome, even shorter
[1, 2, 3].map(&1.method(:+))
# => [2, 3, 4]

In his blog post In Ruby, &method passes you!, Andrew Grimm explains how this all works.

Both snippets via Peter Cooper.

7 notes 0 comments

Mar 29 ’12


Enumerable#each_with_object is quite similar to Enumerable#inject, yet slightly different. From the Ruby 1.9 and Rails 3 API docs:

Iterates the given block for each element with an arbitrary object given, and returns the initially given object.

Iterates over a collection, passing the current element and the memo to the block. Handy for building up hashes or reducing collections down to one object.

evens = (1..10).each_with_object([]) {|i, a| a << i*2 }
#=> [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

%w(foo bar).each_with_object({}) { |str, hsh| hsh[str] = str.upcase }
# => {'foo' => 'FOO', 'bar' => 'BAR'}

As BiHi noted on this tip on Enumerable#inject, its example can be slightly simplified using each_with_object instead of inject:

my_hash = { a: 'foo', b: 'bar' }
# => {:a=>"foo", :b=>"bar"}

my_hash.each_with_object({}) { |(k,v), h| h[k.upcase] = v.upcase }
# => {:A=>"FOO", :B=>"BAR"}

2 notes 0 comments

Mar 27 ’12

Mark Deprecated Code in Ruby

To mark deprecated code in Ruby simply add a comment to the rdoc and call the Kernel#warn method. For example:

class Foo
  # DEPRECATED: Please use useful instead.
  def useless
    warn "[DEPRECATION] `useless` is deprecated.  Please use `useful` instead."

  def useful
    # ...

If you’re using Yard instead of rdoc, your doc comment should look like this:

# @deprecated Please use {#useful} instead

Also, don’t forget to remove the deprecated method in some future release.

Source: Ryan McGeary’s answer on stackoverflow.

9 notes 0 comments

Mar 22 ’12

Using Hash as Recursive Function with Memoization

We can define a new Hash in a smart way by using Hash#new and passing it a block:

h    = {|hash,key| hash[key] = hash[key-1] + hash[key-2]}
h[1] = 0
h[2] = 1

puts h[3] #=> 1
puts h[100] #=> 218922995834555169026

Here an example of famous Collatz Conjecture:

h    = {|hash,n| hash[n] = 1 + (n.odd? ? hash[3*n+1] : hash[n/2])}
h[1] = 1

puts h[100] #=> 26
puts h[1000] #=> 112

via: thoughbot’s blog

3 notes 0 comments

Mar 20 ’12

Block style comments

Wrap a block of code within =begin and =end to comment it out.

# the comment format you're used to
puts "I am evaluated"

puts "I"
puts "am"
puts "commented"
puts "out"

This tip was submitted by Tim Linquist.

6 notes 0 comments

Mar 15 ’12

Method chaining with inject

Aim: perform a method chaining based on hash

Required operation:

ErrorLog.event_eq([3, 7]).subdomain_like("default").user_id_eq(100)


search_opts = { :event_eq => [3, 7], :subdomain_like => "default", :user_id_eq => 100 }


search_opts.inject(ErrorLog) { |memo, (k, v)| memo.send(k, v) }

This tip was submitted by sumskyi.

2 notes 0 comments

Mar 13 ’12

Pretend to generate

If you’re not sure what files a Rails Generator would create for you, just add the -p option (or --pretend) for a dry run:

rails generate model Blog -p

3 notes 0 comments