Ruby Quicktips

Quick Hash to a URL Query trick

danielpietzsch — Sat, 18 Aug 2012 11:03:44 +0200

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

"http://www.example.com?" + { language: "ruby", status: "awesome" }.to_query
# => "http://www.example.com?language=ruby&status=awesome"

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.

Testing CSV file uploads

danielpietzsch — Sun, 22 Jul 2012 10:22:54 +0200

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
  end
    
  respond_to do |format|
    format.html { redirect_to your_path, :notice => "Successfully imported the CSV file." }
  end
end

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')
end

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
Name1,name1@example.com
Name2,name2@example.com
Name3,name3@example.com
eos

  file = Tempfile.new('new_users.csv')
  file.write(csv_rows)
  file.rewind

  assert_difference "User.count", 3 do
    post :csv_import, :file => Rack::Test::UploadedFile.new(file, 'text/csv')
  end

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

Using ActiveRecord to query for times within a range

danielpietzsch — Thu, 03 May 2012 08:01:03 +0200

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

hackerinspiration:

Just discovered this, something I wish I knew a LONG time ago.
Album.where(:created_at => 2.days.ago..Time.now)
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')

Try out your helpers in the Rails console

danielpietzsch — Tue, 01 May 2012 08:01:08 +0200

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\" />"

Creating regular expressions with r{} literals

danielpietzsch — Thu, 19 Apr 2012 08:01:13 +0200

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 = "http://example.com/"

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

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

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

danielpietzsch — Tue, 17 Apr 2012 08:01:36 +0200

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

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

danielpietzsch — Thu, 12 Apr 2012 13:28:37 +0200

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

Post.all.index_by(&:title)
# => { "My first post" => #<Post ...>, "My second post" => #<Post ...>, ... }

Convert a number string in any base to a decimal number

danielpietzsch — Wed, 11 Apr 2012 14:10:14 +0200

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

Two Ruby tricks using method chaining and Procs

danielpietzsch — Wed, 04 Apr 2012 10:02:27 +0200

[1,2,3].each_with_object(1).map(&:+)
# => [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.

Enumerable#each_with_object

danielpietzsch — Thu, 29 Mar 2012 07:00:06 +0200

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"}

Mark Deprecated Code in Ruby

rmdhn — Tue, 27 Mar 2012 11:32:46 +0200

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."
    useful
  end

  def useful
    # ...
  end
end

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.

Using Hash as Recursive Function with Memoization

rmdhn — Thu, 22 Mar 2012 06:00:06 +0100

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

h    = Hash.new {|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.new {|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

Block style comments

danielpietzsch — Tue, 20 Mar 2012 06:00:05 +0100

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

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

=begin
puts "I"
puts "am"
puts "commented"
puts "out"
=end

This tip was submitted by Tim Linquist.

Method chaining with inject

danielpietzsch — Thu, 15 Mar 2012 06:02:05 +0100

Aim: perform a method chaining based on hash

Required operation:

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

Given:

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

Solution:

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

This tip was submitted by sumskyi.

Pretend to generate

danielpietzsch — Tue, 13 Mar 2012 06:00:06 +0100

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

Convert between number bases easily

danielpietzsch — Thu, 08 Mar 2012 06:00:06 +0100

It’s often a requirement in various projects to convert numbers from decimal to text representations of several other bases, such as hexadecimal or binary.
Did you know you can convert to any base from 2 to 36 in one line in Ruby?

Using the Fixnum#to_s method, you can quickly convert any Fixnum object to the textual format of another base:

255.to_s(36) #=> "73"
255.to_s(16) #=> "ff"
255.to_s(2)  #=> "11111111"

This tip was submitted by Nathan Kleyn.

Some Array magic using transpose, map and reduce

danielpietzsch — Tue, 06 Mar 2012 11:06:41 +0100

To add on corresponding elements of several arrays:

a = [1, 2, 3]
b = [4, 5, 6]
c = [7, 8, 9]

[a, b, c].transpose.map { |x| x.reduce :+ }
# => [12, 15, 18]

Given a number of arrays, each contains same number of arrays with the same length. To merge corresponding arrays:

a = [ [1, 2], [3, 4] ]
b = [ [5, 6], [7, 8] ]
c = [ [9, 10], [11, 12] ]

(a.transpose + b.transpose + c.transpose).transpose
# => [[1, 2, 5, 6, 9, 10], [3, 4, 7, 8, 11, 12]]

To do the same job, but with arrays that are not necessarily equal in length:

a = [ [1], [2, 3] ]
b = [ [4, 5], [] ]
c = [ [6,7,8], [9, 10, 11, 12] ]

[a, b, c].transpose.map { |x| x.reduce :+ }
# => [[1, 4, 5, 6, 7, 8], [2, 3, 9, 10, 11, 12]]

Check out the documentation on Array#transpose, Array#map and Enumerable#reduce.

This tip was submitted by Haitham Mohammad.

Quick shortcut to load a SQL file in Rails

offca — Thu, 01 Mar 2012 05:48:38 +0100

You can easily load SQL files like this:

rails db < path_to_sql_file.sql # Rails 3 
script/dbconsole < path_to_sql_file.sql # Rails 2

Around Alias

danielpietzsch — Tue, 28 Feb 2012 07:28:11 +0100

You can write an Around Alias in three simple steps:

You alias a method.
You redefine it.
You call the old method from the new method.

Example:

class String
  alias :orig_length :length

  def length
    "Length of string '#{self}' is: #{orig_length}"
  end  
end

"abc".length
#=> "Length of string 'abc' is: 3"

This tip was submitted by Nimesh Nikum.

Rails' include_root_in_json

danielpietzsch — Thu, 23 Feb 2012 06:00:05 +0100

When rendering JSON from your controllers (or when using to_json directly), Rails 3.1 and above won’t include the root element in the output:

post = Post.first
# => #<Post id: 1, title: "My first blogpost" ...

post.to_json
# => "{\"id\":1,\"title\":\"My first blogpost\", ...}"

To include the root element (post in this example), set ActiveRecord::Base.include_root_in_json to true:

# wrap_paramters.rb
if defined?(ActiveRecord)
  ActiveRecord::Base.include_root_in_json = true
end

Result:

post.to_json
# => "{\"post\":{\"id\":1,\"title\":\"My first blogpost\", ...}}"

In version of Rails < 3.1, including the root element is the default. You can disable it by adding ActiveRecord::Base.include_root_in_json = false to one of your files in config/initializers or in application.rb/environment.rb directly.

More info in the API docs on ActiveModel::Serializers::JSON.