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August 28, 2008
3 thanks

Moved to ActiveRecord::Calculations::ClassMethods

It appears that this method has simply been moved to the module ActiveRecord::Calculations::ClassMethods. You can still use the example listed in the docs here, it will simply call the method ActiveRecord::Calculations::ClassMethods#count.

August 28, 2008 - (v2.1.0)
3 thanks

When using RESTful routes

I had issues using expire_page with RESTful controllers when expiring anything other than the index action because I was basing my expire_page calls off this example.

The solution is to use my_resource_path for example when User with id 5 is updated, you would have to do:

expire_page user_path(user) # or
expire_page formatted_user_path(user, :xml)

This may apply to early versions but I have only tested on v2.1.0

August 27, 2008 - (v1_8_6_287)
3 thanks

Example of raising a custom exception

Create custom exception<br> <pre> class PersonalException < Exception end </pre>

Raise the exception<br> <pre> raise PersonalException.new, “message” </pre>

August 27, 2008
16 thanks

Only attr_accessible attributes will be updated

If your model specified attr_accessible attributes, only those attributes will be updated.

Use attr_accessible to prevent mass assignment (by users) of attributes that should not be editable by a user. Mass assignment is used in create and update methods of your standard controller.

For a normal user account, for example, you only want login and password to be editable by a user. It should not be possible to change the status attribute through mass assignment.

class User < ActiveRecord::Base
  attr_accessible :login, :password

So, doing the following will merrily return true, but will not update the status attribute.

@user.update_attributes(:status => 'active')

If you want to update the status attribute, you should assign it separately.

@user.status = 'active'
August 26, 2008
6 thanks

Prototype hinted_text_field application_helper

Place this in your helper. It will show a message inside the text box and remove it when someone clicks on it. If they don’t enter a value when they leave the field it’ll replace the message. (Requires javascript :defaults).

def hinted_text_field_tag(name, value = nil, hint = "Click and enter text", options={})
  value = value.nil? ? hint : value
  text_field_tag name, value, {:onclick => "if($(this).value == '#{hint}'){$(this).value = ''}", :onblur => "if($(this).value == ''){$(this).value = '#{hint}'}" }.update(options.stringify_keys)

# inside form_for example

hinted_text_field_tag :search, params[:search], "Enter name, brand or mfg.", :size => 30  
# => <input id="search" name="search" onblur="if($(this).value == ''){$(this).value = 'Enter name, brand or mfg.'}" onclick="if($(this).value == 'Enter name, brand or mfg.'){$(this).value = ''}" size="30" type="text" value="Enter name, brand or mfg." />
August 26, 2008
10 thanks

Customizing prompt

The :prompt option not only accepts a boolean value. It can also be given a string to define another than the standard prompt ‘Please select’. Referring to the example it could read:

collection_select(:post, :author_id, Author.find(:all),
                  :id, :name_with_initial,
                 {:prompt => 'Please select the author of this post'})
August 25, 2008 - (v1.1.6 - v2.1.0)
3 thanks

Delete collections with check box tags

Following autonomous’ directions works wonders on /edit but needs slight modifications when dealing with pagination on /index.

In a /index type listing page we can no longer assume that the list of ids coming back represents changes to all objects so we need to provide some context, that the list of object modifications in our params array is a list of modifications for some set of objects.

We can only assume subsets because pagination or filtering may reduce the set of objects we’re working on.

In our case we had a user management page which listed all users and showed whether they were activated or not. The following code is what we used to ensure that modifications to the first page of objects wouldn’t affect all the other pages.


<% @users.each do |user| %>
  <%= hidden_field_tag('seen[]', user.id) -%>
  <%= check_box_tag 'activated[]', user.id -%>
<% end %>


def index
  if request.post?
    activated_ids = params[:activated].collect {|id| id.to_i} if params[:activated]
    seen_ids = params[:seen].collect {|id| id.to_i} if params[:seen]

    if activated_ids
      seen_ids.each do |id|
        r = User.find_by_id(id)
        r.activated = activated_ids.include?(id)
August 25, 2008 - (>= v2.1.0)
6 thanks

Rake tasks for gem dependencies

You can manage installation and other tasks for these dependencies with rake tasks, for example:

rake gems:install              # Installs all required gems for this application
rake gems:unpack               # Unpacks the specified gem into vendor/gems

To get all rake tasks about gems:

rake -T gems
August 25, 2008 - (v2.1.0)
5 thanks

Disable default date

If you want a date selector that initially doesn’t have a date selected you can pass it the option :include_blank.

date_select("project", "due_date", :include_blank => true)
August 25, 2008
5 thanks

%w(true false) != [true, false]

Don´t confuse the right:

validates_inclusion_of :published, :in => [true, false]

with the wrong:

validates_inclusion_of :published, :in => %w(true false)


%w(true false) == ["true", "false"]
August 23, 2008
4 thanks

Needs requiring 'enumerator' to work

This method needs that you

require 'enumerator'

for this method to be available.

August 23, 2008
3 thanks

Include two level has many model example

class Issue < ActiveRecord::Base

  has_many :journals

class Journal < ActiveRecord::Base
  belongs_to :issue
  has_many :details, :class_name => "JournalDetail", :dependent => :delete_all

class JournalDetail < ActiveRecord::Base
  belongs_to :journal


issue = Issue.find(:first, :include => {:journals => :details}

log record follow:

SELECT * FROM `issues` LIMIT 1
SELECT `journals`.* FROM `journals` WHERE (`journals`.`journalized_id` IN (1) and `journals`.`journalized_type` = 'Issue' AND (dustbin <> 1))
SELECT `journal_details`.* FROM `journal_details` WHERE (`journal_details`.journal_id IN (1,2,876177898,935815637))

when execute follow code, then not build sql sentent:

August 22, 2008
4 thanks

Doesn't add an index

Typically you will want to have an index on foreign keys but this method doesn’t assume that. Outside of the create_table block you should follow this with add_index :

add_index :table_name, :goat_id
# and, if polymorphic:
add_index :table_name, :goat_type
August 22, 2008 - (>= v2.1.0)
13 thanks

Specifying :include no longer necessarily joins the association

Before Rails 2.1, adding an :include=>[:association] in your find method caused ActiveRecord to generate SQL using a join. Since 2.1, it MAY NOT execute as a join.

The join executes a large query and returned potentially duplicate records for a one-to-many association. After 2.1, the query is broken down and eager-loaded using an additional query per association, passing the set of id’s to load, and avoiding the duplicate rows.

The new method eliminates duplicates, but can incur more database overhead. If you are loading a very large set of records (more than a “page”), you may need to “force” the join or use find_by_sql instead.

When you specify a “table.column” syntax within a

:conditions=>["child.name=?", name]  



then ActiveRecord will build the older, full query with the join because you are referencing columns from another table to build. This will cause the duplicate rows to reappear.

Whenever you reference a column from another table in a condition or order clause, ALWAYS use the table name to prefix the column, even if it not ambiguous among the tables involved. Otherwise the query will not be executed as a join and you will receive an SQL error referencing the “missing” column.

You can “force” a join by adding a reference to the other tables in your :conditions or :options parameters, even if the test or sort is irrelevant.

August 20, 2008
5 thanks

Iterate and join blocks

Following LacKac’s idea, we can write render_join (useful to render a collection with a small chunks of code, where a render :partial + :spacer_template would be overkill):

def render_join(collection, join_string, &block)
  output = collection.collect do |item| 
    capture(item, &block)
  concat(output, block.binding)

An example of use:

<% render_join(@items, '<br />') do |item| %>
   <p>Item title: <%= item.title %></p>
<% end %>
August 20, 2008
4 thanks

Current Database Name

The MySQL database adapter extends this and allows you to call


to get the current databases name. Useful when you are actively changing the database you are connected to and sometimes need to check the current one.


August 20, 2008
3 thanks

Current Database Name

The MySQL database adapter extends this and allows you to call


to get the current databases name. Useful when you are actively changing the database you are connected to and sometimes need to check the current one.


August 19, 2008 - (v2.1.0)
8 thanks

preload_associations manually

Usually you preload associations using :include => [ ... ]. In Rails 2.1 each association is fetched with a separate query. Something like:

Post.find(:all, :include => [:tags, :user])

will produce 3 queries - each for posts, tags and users.

But sometimes you have a complex query, which uses :joins => :other_association and conditions between multiple tables, but not the ones you need to include. Then everything is mixed back in one query like in old versions of Rails.

Another case may be when it is not possible to use :include at all, for example while using find_by_sql, but you still want/need to preload associated records.

In rails 2.1 find uses preload_associations internally, when it is possible (There are no joins or conditions between tables).

So then you can preload asociations manually from within your model:

class Post < ActiveRecord::Base

has_many :tags
belongs_to :user

def self.find_complex_with_includes
  posts = find_by_sql(...) # or find(:all, :joins => .....)
  preload_associations(posts, [:tags, :user])


and then do

@posts = Post.find_complex_with_includes

August 19, 2008 - (v2.1.0)
6 thanks

Namespace or modules in routes

If you have grouped controllers into a module, e.g. admin then you can specify this in the routes using the namespace method:

map.namespace :admin do |admin|
  admin.resources :categories

which will map the categories resource giving urls like



It will also generate the named routes such as new_admin_category_url and admin_category_path

August 19, 2008
6 thanks

script/generate syntax

To add a post_id field to a comments table, run this:

script\generate migration add_post_id_to_comment post_id:integer

See that it´s not the table name(plural), but the model name(singular),<br /> and post_id:references, does not works like in create_table.

This is the generated migration:

class AddPostIdToComment < ActiveRecord::Migration
 def self.up
   add_column :comments, :post_id, :integer

 def self.down
   remove_column :comments, :post_id
August 17, 2008
6 thanks

Re: Convert an Array of Arrays to a Hash using inject

If you’re sure you have a two-level array (no other arrays inside the pairs) and exactly two items in each pair, then it’s faster and shorter to use this:

array = [['A', 'a'], ['B', 'b'], ['C', 'c']]
hash = Hash[*array.flatten]

For more than two-level deep arrays this will give the wrong result or even an error (for some inputs).

array = [['A', 'a'], ['B', 'b'], ['C', ['a', 'b', 'c']]]
hash = Hash[*array.flatten]
# => {"A"=>"a", "B"=>"b", "C"=>"a", "b"=>"c"}

But if you’re running Ruby 1.8.7 or greater you can pass an argument to Array#flatten and have it flatten only one level deep:

# on Ruby 1.8.7+
hash = Hash[*array.flatten(1)]
# => {"A"=>"a", "B"=>"b", "C"=>["a", "b", "c"]}
August 17, 2008
4 thanks

Regexes with groups and split

When you use a Regex with capture groups, all capture groups are included in the results (interleaved with the “real” results) but they do not count for the limit argument.


=> ["abc", ",", "cde", ",", "efg", ",", "ghi"]
=> ["abc", ".", ",", "cde", ".", ",", "efg", ".", ",", "ghi"]
=> ["abc", ".,", ",", "cde", ".,", ",", "efg", ".,", ",", "ghi"]
"abc.,cde.,efg.,ghi".split(/(.(,))/, 2)
=> ["abc", ".,", ",", "cde.,efg.,ghi"]
"abc.,cde.,efg.,ghi".split(/(.(,))/, 3)
=> ["abc", ".,", ",", "cde", ".,", ",", "efg.,ghi"]
August 17, 2008
7 thanks

Using sweepers in script/runner

If you need to use some of your sweepers in a script/runner script or some rake task you can use this snipped:

require 'action_controller/test_process'

sweepers = [ProductSweeper, UserSweeper]

ActiveRecord::Base.observers = sweepers

controller = ActionController::Base.new
controller.request = ActionController::TestRequest.new
controller.instance_eval do
  @url = ActionController::UrlRewriter.new(request, {})

sweepers.each do |sweeper|
  sweeper.instance.controller = controller

Your script will fire the ActiveRecord callbacks defined in that sweepers and you can use expire_cache, expire_fragment and also the routing helpers you have defined (hash_for_user_path, hash_for_product_path, etc.).

August 17, 2008
6 thanks

Explanation about :dependent option

It may seem that :dependent option is only used when the object that has the collection is destroyed, but it is also used every time a associated object is deleted, so if you use


your object will be deleted, destroyed or nullified, depending on the value of :dependent option.

With has_many :through associations this option is ignored at least in versions up to 2.1.0, so even if you set :dependent option to :destroy, your join objects will be deleted, not firing any callbacks you have set on destroy events.

If you need to act when your join model is deleted you can use a sweeper or an observer and the association callbacks like this:

# product.rb
class Product
  has_many :categorizations
  has_many :categories, :through => :categorizations,
    :before_remove => :fire_before_remove_in_categorizations

  def fire_before_remove_in_categorizations(category)
    categorization = self.categorizations.find_by_category_id(category.id)
    categorization.class.notify_observers(:before_remove, categorization)

# categorization_sweeper.rb
# do not forget to load this sweeper during initialization
class CategorizationSweeper < ActionController::Caching::Sweeper
  observe Categorization

  def before_remove(categorization)
    # expire_cache, expire_fragment, whatever

One thing you should be aware of it is that you are using before_remove, so you have to be careful because your record may be not be removed (another callback raising an exception or the database not deleting the record) so you can not be sure your object will be delete. Expiring caches is safe because even if your record is not destroyed your cache will be regerated correctly.

You can not use after_remove, because at that point the join model do not exists anymore, so you can not fire its callbacks. But you have the model id and the associated model id, so if you do not need expiring caches maybe you can use this approach (expiring caches can be only done in a sweeper or in a controller, but with after_remove you are bound to your model).

August 15, 2008
9 thanks

anything matcher

The anything matcher will match any ruby object:

1.should == anything
nil.should == anything
'string'.should == anything

var.should_receive(:method).with(param1, anything)
August 15, 2008
4 thanks

Cheking if a number is prime?

It’s a class for generating an enumerator for prime numbers and traversing over them.

It’s really slow and will be replaced in ruby 1.9 with a faster one.

Note: if you just want to test whether a number is prime or not, you can use this piece of code:

class Fixnum
  def prime?
    ('1' * self) !~ /^1?$|^(11+?)\1+$/

August 15, 2008
8 thanks

Optional Argument for detect/find [Not Documented]

detect/find’s optional argument lets you specify a proc or lambda whose return value will be the result in cases where no object in the collection matches the criteria.

classic_rock_bands = ["AC/DC", "Black Sabbath","Queen", "Ted Nugent and the Amboy Dukes","Scorpions", "Van Halen"]
default_band = Proc.new {"ABBA"}
classic_rock_bands.find(default_band) {|band| band > "Van Halen"}
=> "ABBA"


random_band = lambda do
  fallback_bands = ["Britney Spears", "Christina Aguilera", "Ashlee Simpson"]
classic_rock_bands.find(random_band) {|band| band > "Van Halen"}
=> "Britney Spears"
August 15, 2008
3 thanks

Convert a Hash to an Array of Arrays using map

Although you’ll always have to_a and it’s faster, this trick is too cool to ignore…

When the block is omitted, collect or map uses this implied block: {|item| item}, which means when applied on an hash without a block, collect/map returns an array containing a set of two-item arrays, one for each key/value pair in the hash. For each two-item array, item 0 is the key and item 1 is the corresponding value.

burgers = {"Big Mac" => 300, "Whopper with cheese" => 450, "Wendy's Double with cheese" => 320}

=> [["Wendy's Double with cheese", 320], ["Big Mac", 300], ["Whopper with cheese", 450]]

see also:

August 15, 2008
3 thanks

Using any? on Empty Arrays and Hashes

When applied to an empty array or hash, with or without a block, any? always returns false. That’s because with an empty collection, there are no values to process and return a true value.