Flowdock

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March 27, 2009
4 thanks

multiple filter example

actually you can have it even shorter with:

before_filter :authorize, :set_locale, :except => :login
March 23, 2009 - (v2.3.2)
4 thanks

So, how do you enable db sessions?

First, run:

rake db:sessions:create

Then, run your pending migrations. This will create the migration you need to run in order to create the sessions table.

Second, go into config/environment.rb and uncomment or put in:

config.action_controller.session_store = :active_record_store
config.action_controller.session = {
   :session_key => '_your_session_name_here',
   :secret      => 'SOME_CRYPTOGRAPHICALLY_SECURE_KEY'
 }

Third, get yourself a secure key with:

rake secret

And finally, paste your new key into the :secret above.

March 21, 2009
4 thanks

Passing optional arguments with defaults to a named_scope

An easy way to do this. (This also shows how you can use joins in a named_scope as well.)

Class User << ActiveRecord::Base
belongs_to :semester 

named_scope :year, lambda { |*year|
  if year.empty? || year.first.nil?
    { :joins => :semester, :conditions => ["year = #{CURRENT_SEMESTER}"]}
  else
    { :joins => :semester, :conditions => ["year = #{year}"]}
  end
  }

end

You can then call:

User.year     # defaults to CURRENT_SEMESTER constant
User.year()  # same as above
User.year(nil)  # same as above; useful if passing a param value that may or may not exist, ie, param[:year]
User.year(2010)
March 21, 2009
7 thanks

Use helpers in your ActionMailer views

It’s very easy to give your mailer access to helpers:

# Let your mailer user the ApplicationHelper methods
class MyMailer < ActionMailer::Base
  helper :application
end
March 20, 2009 - (>= v2.0.0)
9 thanks

Use the current URL, with changes

You can use the current URL, whatever it is, with changes, as in:

# Create a link to the current page in RSS form
url_for(:overwrite_params => {:format => :rss})

This can be super-helpful because it preserves any GET params (like search parameters)

March 18, 2009
4 thanks

Better autopad numbers

There is a much better way than to use diwadn’s method if you want to pad numbers with zeros. Here’s my recommended way to do it:

"Number: %010d" % 12345 #=> "Number: 0000012345"

It’s very easy. First we begin our placeholder with “%”, then we specify a zero (0) to signify padding with zeros. If we omitted this zero, the number would be padded with spaces instead. When we have done that, just specify the target length of the string. At last a single “d” is placed to signify that we are inserting a number.

Please see String#% and Kernel#sprintf for more information about how to do this.

Here’s another example of how to do it:

12345.to_s.rjust(10, "0") #=> "0000012345"

See String#rjust for more information.

Any of these methods are a lot better than the method outlined below.

March 12, 2009
3 thanks
March 12, 2009
12 thanks

User a block to extend your associations

You can use blocks to extend your associations with extra methods.

code sample

has_many :children, :dependent => :destroy do
  def at(time)
    proxy_owner.children.find_with_deleted :all, :conditions => [
      "created_at <= :time AND (deleted_at > :time OR deleted_at IS NULL)", { :time => time }
    ]        
  end      
end

Model.children.each # do stuff
Model.children.at( 1.week.ago ).each # do old stuff

you must use ‘proxy_owner’ to link back to your model.

March 10, 2009 - (>= v2.1.0)
8 thanks

Use lambda to avoid caching of generated query

If you’re using a named_scope that includes a changing variable you need to wrap it in a lambda to avoid the query being cached and thus becoming unaffected by future changes to the variable, example:

named_scope :translated, :conditions => { :locale => I18n.locale }

Will always return the same locale after the first hit even though I18n.locale might change. So do this instead:

named_scope :translated, lambda { { :conditions => { :locale => I18n.locale } } }

Ugly, but at least it’s working as we expect it…

March 5, 2009
7 thanks

String#match will match single token only

>> s = “{{person}} ate {{thing}}”

> “{{person}} ate {{thing}}”

>> r = /{{(.*?)}}/

> {{}}

>> s.match®.captures

> [“person”]

Using String#scan pulls out all tokens you were searching for:

>> s.scan®.flatten

> [“person”, “thing”]

March 4, 2009
10 thanks

Differences between normal or-assign operator

Differences between this method and normal memoization with ||=:

  • memoize works with false/nil values

  • Potential arguments are memoized

Take the following example:

def allowed?
  @allowed ||= begin
    # Big calculation
    puts "Worked"
    false
  end
end

allowed? # Outputs "Worked"
allowed? # Outputs "Worked" again

Since @allowed is set to false (this is also applicable with nil), the ||= operator will move on the the next statement and will not be short-circuited.

When you use memoize you will not have this problem.

def allowed?
  # Big calculation
  puts "Worked"
  false
end
memoize :allowed?

allowed? # Outputs "Worked"
allowed? # No output

Now, look at the case where we have parameters:

def random(max=10)
  @random ||= rand(max)
end

random     # => 4
random     # => 4 -- Yay!
random(20) # => 4 -- Oops!

Better use memoize again!

def random(max=10)
  rand(max)
end
memoize :random

random     # => 6
random     # => 6 -- Yay!
random(20) # => 12 -- Double-Yay!
random     # => 6 -- Head a'splode
March 4, 2009
5 thanks

Usage

This defines attr_accessors at a class level instead of instance level.

class Foo
  cattr_accessor :greeting
end

Foo.greeting = "Hello"

This could be compared to, but is not the same as doing this:

class Bar
  class << self
    attr_accessor :greeting
  end
end

Bar.greeting = "Hello"

The difference might not be apparent at first, but cattr_accessor will make the accessor inherited to the instances:

Foo.new.greeting #=> "Hello"
Bar.new.greeting # NoMethodError: undefined method `greeting' for #<Bar:0x18e4d78>

This inheritance is also not copy-on-write in case you assumed that:

Foo.greeting  #=> "Hello"
foo1, foo2 = Foo.new, Foo.new

foo1.greeting = "Hi!"

Foo.greeting  #=> "Hi!"
foo2.greeting #=> "Hi!"

This makes it possible to share common state (queues, semaphores, etc.), configuration (max value, etc.) or temporary values through this.

March 3, 2009
9 thanks

File class documentation

Most of the File class documentation is located in IO class docs. What you see here is what ‘ftools’ gives you.

February 27, 2009
6 thanks

Extend with an anonymous module

You can extend with an anonymous module for one-off cases that won’t be repeated:

belongs_to :container, :polymorphic => true, :extend => ( Module.new do
    def find_target
      ...
    end
  end )

The parentheses are important, will fail silently without them.

February 24, 2009
9 thanks

Specialized versions of find with method_missing

Check ActiveRecord::Base.method_missing for documentation on the family of “magic” find methods (find_by_x, find_all_by_x, find_or_create_by_x, etc.).

February 24, 2009 - (>= v2.2.1)
5 thanks

ATM does not work in Rails 2.3 Edge

add to test/spec_helper to make it work again…

#spec_helper / test_helper
include ActionController::TestProcess
February 23, 2009 - (>= v2.0.0)
6 thanks

Nested with_options

You can nest with_options blocks, and you can even use the same name for the block parameter each time. E.g.:

class Product
  with_options :dependent => :destroy do |product|
    product.with_options :class_name => 'Media' do |product|
      product.has_many :images, :conditions => {:content_type => 'image'}
      product.has_many :videos, :conditions => {:content_type => 'video'}
    end

    product.has_many :comments
  end
end
February 22, 2009
3 thanks

CAUTION! :frequency option description is misleading

To use event-based observer, don’t supply :frequency param at all. :frequency => 0 causes JS error.

Use this option only if time-based observer is what you need.

February 20, 2009
5 thanks

Static and dynamic attachments

You can attach static files directly:

attachment :content_type => "image/jpeg", :body => File.read("someimage.jpg")

and you can also define attachments dynamically by using a block:

attachment "text/csv" do |a|
  a.body = my_data.to_csv
end
February 18, 2009
4 thanks

Turn off for individual controllers/actions

To disable protection for all actions in your controller use skip_before_filter:

skip_before_filter :verify_authenticity_token

You can also pass :only and :except to disable protection for specific actions, e.g:

skip_before_filter :verify_authenticity_token, :only => :index
February 17, 2009
4 thanks

Date_select with assert_valid_keys

If you are using date_select with assert_valid_keys you have to allow 3 parameters named field(1i), field(2i) and field(3i).

For example with field

date_select("post", "written_on")

You have to allow following fields:

params[:post].assert_valid_keys( 
  'written_on(1i)', 'written_on(2i)', 'written_on(3i)'
)
February 17, 2009
7 thanks

Usage examples

Basic usage:

User.should_receive(:find).with(:all, anything).and_return("hello world")

Now:

User.find(:all, :conditions => "foo")  #=> "hello world"

But you can also use blocks for more complex matching logic. For example:

User.should_receive(:find) { |*args|
  if args.size == 2
    "received two arguments"
  else
    "something else"
  end
}.at_least(:once)

Now:

User.find(:all, :conditions => "bar")  #=> "received two arguments"
User.find(5)                           #=> "something else"

Of course normally you’d return mocks instead of strings.

February 17, 2009
9 thanks

Empty elements

If you want to output an empty element (self-closed) like “br”, “img” or “input”, use the tag method instead.

February 16, 2009
5 thanks

Usage example

Some examples:

# Remove even numbers
(1..30).reject { |n| n % 2 == 0 }
# => [1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29]

# Remove years dividable with 4 (this is *not* the full leap years rule)
(1950..2000).reject { |y| y % 4 != 0 }
# => [1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2000]

# Remove users with karma below arithmetic mean
total = users.inject(0) { |total, user| total += user.karma }
mean = total / users.size
good_users = users.reject { |u| u.karma < mean }
February 13, 2009
3 thanks

New test syntax

You can use either one and even mix in the same test case if you want:

class Test < Test::Unit::TestCase
  # old way to define a test method (prefix with test_)
  def test_should_be_valid_without_content
    assert Comment.new.valid?
  end

  # new way to define a test
  test "should be valid without content" do
    assert Comment.new.valid?
  end
end
February 12, 2009
4 thanks

Real life use

If you’re wondering what the base64 format is used for, here are some examples:

  • HTTP Basic authentication: encode your username and password as one string, and add it as a header of an HTTP request. When a page requiring basic authentication gets called from a browser it results in a generic Username/Password dialog from that browser. See also http://en.wikipedia.org/wiki/Basic_access_authentication

  • Encode the binary content of images to base64 and embed it in XML documents, for example in web services

  • For more information see http://en.wikipedia.org/wiki/Base64

Just note that the encoded (character) data is about 30% larger than un-encoded (binary) data.

February 12, 2009
4 thanks

Binary files

Another real important flag is b when dealing with binary files. For example to download an mp3 from the internet you need to pass the b flag or the data will be screwed up:

# Downloads a binary file from the internet
require 'open-uri'
url = "http://fubar/song.mp3"
open(url, 'rb') do |mp3|
  File.open("local.mp3", 'wb') do |file|
    file.write(mp3.read)
  end
end

Don’t say you haven’t been warned. :)

February 12, 2009
3 thanks

Other regular-expression modifiers

Likewise you can set Regexp::IGNORECASE directly on the regexp with the literal syntax:

/first/i
# This will match "first", "First" and even "fiRSt"

Even more modifiers

  • o – Perform #{} interpolations only once, the first time the regexp literal is evaluated.

  • x – Ignores whitespace and allows comments in * regular expressions

  • u, e, s, n – Interpret the regexp as Unicode (UTF-8), EUC, SJIS, or ASCII. If none of these modifiers is specified, the regular expression is assumed to use the source encoding.

Literal to the rescue

Like string literals delimited with %Q, Ruby allows you to begin your regular expressions with %r followed by a delimiter of your choice.

This is useful when the pattern you are describing contains a lot of forward slash characters that you don’t want to escape:

%Q(http://)
# This will match "http://"
February 12, 2009
4 thanks

Literal syntax

As you propably know you can create an Array either with the constructor or the literal syntax:

Array.new == []
# => true

But there is also another nice and concise literal syntax for creating Arrays of Strings:

["one", "two", "three"] == %w[one two three]
# => true

You can use any kind of parenthesis you like after the %w, either (), [] or {}. I prefer the square brackets because it looks more like an array.