Ruby Quicktips
This blog is dedicated to deliver short, interesting and practical tidbits of the Ruby language and Ruby on Rails framework. Read more...
Your submissions are more than welcome!
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:
"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
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
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 => 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
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
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]
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
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
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
[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.
Enumerable#each_with_object
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
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
endIf you’re using Yard instead of rdoc, your doc comment should look like this:
# @deprecated Please use {#useful} insteadAlso, don’t forget to remove the deprecated method in some future release.
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.new {|hash,key| hash[key] = hash[key-1] + hash[key-2]}
h[1] = 0
h[2] = 1
puts h[3] #=> 1
puts h[100] #=> 218922995834555169026Here 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] #=> 112via: thoughbot’s blog
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"
=begin
puts "I"
puts "am"
puts "commented"
puts "out"
=endThis tip was submitted by Tim Linquist.
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)
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
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