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February 23, 2009 - (<= v2.2.1)
1 thank

You can't have many :through with habtm

Imagine the following

a has_many b
b has_and_belongs_to_many c
a has_many c :through => b

a.b works fine

b.c works fine

a.c throws an error!

has_many :through where the through association is a habtm is not supported in Rails. The error is:

ActiveRecord::HasManyThroughSourceAssociationMacroError: Invalid source reflection macro :has_and_belongs_to_many for has_many :stories, :through => :subcategories. Use :source to specify the source reflection

Specifying the source reflection still won’t help you though, because this kind of has_many :through isn’t supported at all.

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'}

    product.has_many :comments
February 23, 2009
2 thanks

Check if value is included in array of valid values

If you want to check the value of an attribute using an array of valid values, the array has to be defined before the validation, so

validates_inclusion_of :name, :in => VALID_NAMES
VALID_NAMES = %w(Peter Paul Mary)

won’t work, but

VALID_NAMES = %w(Peter Paul Mary)
validates_inclusion_of :name, :in => VALID_NAMES


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
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:

  '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")


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"
    "something else"


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 17, 2009
2 thanks

Remember to sanitize name

While useful when in need of richer markup inside a link, the name parameter isn’t sanitized or escaped and thus should be escaped when its content can’t be guaranteed to be safe.


link_to(url, url)

may cause problems with character entities if url contains ampersands.

Correct usage
link_to(h(url), url)

This applies to all dynamic content.

February 17, 2009
2 thanks

See column

See the end part of the docs on column for example uses.

February 16, 2009
1 thank

See max

See max for comments and more usage examples.

February 16, 2009
2 thanks

Capping values

This method is very useful when you want to cap values:

# minimum ≤ value 
value = [input.to_i, minimum].max

# value ≤ maximum
value = [input.to_i, maximum].min

# minimum ≤ value ≤ maximum
value = [ [input.to_i, minimum].max, maximum ].min

# Practical example: Make sure destination is within container
destination.x = [ [current.x + current.velocity.x, 0].max, container.width  ].min
destination.y = [ [current.y + current.velocity.y, 0].max, container.height ].min
February 16, 2009
6 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 16, 2009
1 thank

Reverse of this

If you want to do the reverse of this, e.g. go from a specific date and back to a certain day of the previous week, you can implement it like this:

def last_week(day = :monday)
  days_into_week = { :monday => 0, :tuesday => 1, :wednesday => 2, :thursday => 3, :friday => 4, :saturday => 5, :sunday => 6}
  result = (self - 7).beginning_of_week + days_into_week[day]
  self.acts_like?(:time) ? result.change(:hour => 0) : result

If you do not want to make your own method of this, but just want to do it in a regular chaining of date methods (like Date.today.next_year.at_midnight), you can do it like the following:

(date - 7).next_week(:tuesday) # Tuesday, last week

Please note that you just need to subtract 7 if you want to move back a week. Only use these methods if you want to go to a specific day of the week.

February 16, 2009
1 thank

Reverse naming

The reverse of this is last_month and not previous_month, like one might believe from the naming.

February 16, 2009
1 thank

Reverse naming

The reverse of this is last_year and not previous_year, like one might believe from the naming.

February 15, 2009
0 thanks

use #collect instead of #each

The earlier reminder to use #collect instead of #each applies regardless of whether the tag is nested or not.

This is counterintuitive, as #collect returns an array of strings of HTML tags, but ActionView renders it properly.

February 14, 2009
1 thank

Clear and simple rescue

noxyu3m, your code is rescuing all exceptions, not just ActiveRecord::RecordInvalid.

I think this syntax is a bit more clear than using the global variable.

def create
  @model = Model.new(params[:model)
rescue => err                          # rescues all exceptions
February 14, 2009
0 thanks

Simple rescue

Take it easy:

def create
  @model = Model.new(params[:model)

Global variable !$ refers to the Exception object.

February 13, 2009
1 thank

throws exception

when use use Model.find([1,2,3,4])

throws exception if no record exists with any of this ID

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?

  # new way to define a test
  test "should be valid without content" do
    assert Comment.new.valid?
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
0 thanks

using collection=objects

It will fire one insert query per new record

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|

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:

# 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:

# 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.

February 12, 2009
2 thanks

Use this!

You should raise your own ArgumentError in methods to notify users of your class, if you think certain kinds of arguments aren’t acceptable.

def transfer_money(amount)
  unless amount.is_a?(Number)
    raise ArgumentError.new("Only numbers are allowed")
  # ... Do the actual work