Ruby Quicktips

Using ActiveRecord to query for times within a range

danielpietzsch — Thu, 03 May 2012 18:01:03 +1200

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

danielpietzsch — Tue, 01 May 2012 18:01:08 +1200

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 18:01:13 +1200

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 18:01:36 +1200

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 23:28:37 +1200

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 — Thu, 12 Apr 2012 00:10:14 +1200

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 20:02:27 +1200

[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 18:00:06 +1300

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 22:32:46 +1300

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 18:00:06 +1300

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 18:00:05 +1300

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 18:02:05 +1300

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 18:00:06 +1300

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 18:00:06 +1300

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 23:06:41 +1300

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 17:48:38 +1300

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 19:28:11 +1300

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 18:00:05 +1300

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.

Naming the Process

danielpietzsch — Tue, 21 Feb 2012 18:00:05 +1300

You can set the name of the current Ruby process, the one that you would see from the ps command for example.
Simply assign a string to the global variable $PROGRAM_NAME:

$PROGRAM_NAME = 'Hello from Rubyland!'
puts $0 # This is an alias for the same thing.

This is a great way for long running scripts or daemon processes to communicate status information to people who are looking in on them.

5.times do |i|
  $PROGRAM_NAME = "Ruby Quicktips Example: On iteration #{i}"
  sleep 5 # I'm really busy!!
end

Execute something like this in your terminal:

ps x | grep Quicktips

This tip was submitted by Jesse Storimer.

Making class methods private

danielpietzsch — Thu, 16 Feb 2012 18:00:00 +1300

This does not work:

class Foo
  private
  
  def self.bar
  end
end

Foo.bar will be public.
To make it private, you can use Module#private_class_method:

class Foo
  def self.bar
  end

  private_class_method :bar
end

…or define it differently:

class Foo
  class << self
    private
        
    def bar
    end
  end
end

This tip was submitted by two-bit-fool.