Flowdock

Good notes posted to Ruby on Rails

RSS feed
June 18, 2010
7 thanks

multiple attributes with the same validations

You can list multiple attributes if they share the same validations

validates :title, :body, :presence => true

sending the attributes as an array will return an error

validates [:title, :body], :presence => true
#=> ArgumentError: Attribute names must be symbols
May 31, 2010
4 thanks

Naming fragment cache

One of the common ways of using fragment caching is to cache content that’s shared across the site (eg. left navigation, menus, widgets etc.) that looks and works the same regardless of the name of the action or controller calling it. In such cases it’s very easy to just use named fragment caching eg.:

<% cache('left_nav') do -%>
  <%= display_left_nav -%>
<% end -%>
April 3, 2010 - (>= v2.2.1)
3 thanks

Careful with this method.

Despite the name and description, it will actually update any changed fields on the model rather than just the desired attribute.

def update_attribute(name, value)
  send(name.to_s + '=', value)
  save(false)
end

See? Use update_all and pass in the model ID as a condition, instead.

March 13, 2010
3 thanks

Can be used with has_many associations

You can also use this to validate that a has_many association has a specified number of records on the other end:

has_many :members

validates_length_of :members, :minimum => 1
March 11, 2010
3 thanks

Available statuses

All the available statuses (extracted from SYMBOL_TO_STATUS_CODE hash) in a slightly more readable form:

:continue                        => 100
:switching_protocols             => 101
:processing                      => 102
:ok                              => 200
:created                         => 201
:accepted                        => 202
:non_authoritative_information   => 203
:no_content                      => 204
:reset_content                   => 205
:partial_content                 => 206
:multi_status                    => 207
:im_used                         => 226
:multiple_choices                => 300
:moved_permanently               => 301
:found                           => 302
:see_other                       => 303
:not_modified                    => 304
:use_proxy                       => 305
:temporary_redirect              => 307
:bad_request                     => 400
:unauthorized                    => 401
:payment_required                => 402
:forbidden                       => 403
:not_found                       => 404
:method_not_allowed              => 405
:not_acceptable                  => 406
:proxy_authentication_required   => 407
:request_timeout                 => 408
:conflict                        => 409
:gone                            => 410
:length_required                 => 411
:precondition_failed             => 412
:request_entity_too_large        => 413
:request_uri_too_long            => 414
:unsupported_media_type          => 415
:requested_range_not_satisfiable => 416
:expectation_failed              => 417
:unprocessable_entity            => 422
:locked                          => 423
:failed_dependency               => 424
:upgrade_required                => 426
:internal_server_error           => 500
:not_implemented                 => 501
:bad_gateway                     => 502
:service_unavailable             => 503
:gateway_timeout                 => 504
:http_version_not_supported      => 505
:insufficient_storage            => 507
:not_extended                    => 510
March 4, 2010
3 thanks

Re: Caveat when using dynamic layouts

Since there’s no way to edit posts on here, I need to correct myself and say that what I posted before doesn’t work, since you can’t specify layout multiple times:

class OrdersController < BaseController
  layout :determine_layout, :only => :new
  layout "public", :except => :new
  # ...
end

So don’t do that. The only way to ensure that the other actions get the default theme is to drop :only/:except and do the conditions yourself:

class OrdersController < BaseController
  layout :determine_layout

private
  def determine_layout
    %w(new).include?(action_name) ? "some_layout" : "public"
  end
end

All this to say, beware of :only/:except – they aren’t as useful as you think they are.

February 27, 2010
4 thanks

Caveat when using dynamic layouts

Worth noting that if you have a controller which inherits from another controller which has a layout, and in this child controller you’re determining the layout at runtime using a method for specific actions, the other actions you are excluding will not inherit the layout from the parent controller.

For example, if you’ve got this

class BaseController < ApplicationController
  layout "public"
end
class OrdersController < BaseController
  layout :determine_layout, :only => :new
  # index, show, new, create, edit, update, destroy ...
end

then OrdersController#index, #show, and #edit won’t get the “public” layout – in fact they won’t get a layout at all. So you’ll need to do this instead:

class OrdersController < BaseController
  layout :determine_layout, :only => :new
  layout "public", :except => :new
  # ...
end
February 26, 2010
3 thanks

default_scope on create

If you specify :conditions in your default_scope in form of a Hash, they will also be applied as default values for newly created objects. Example:

class Article
  default_scope :conditions => {:published => true}
end

Article.new.published? # => true

However:

class Article
  default_scope :conditions => 'published = 1'
end

Article.new.published? # => false
February 23, 2010
3 thanks

Easy workaround for missing :through option

Note that belongs_to does not support :through option like has_many (although IMHO it would make sense in some cases), but you can easily simulate it with delegate.

For example:

class Person < ActiveRecord::Base
  belongs_to :team
  ...
end
class Task < ActiveRecord::Base
  belongs_to :person
  delegate :team, :to => :person
end

There is of course more ways to do it, but this seems to be the easiest to me.

February 16, 2010 - (>= v2.1.0)
3 thanks

Extract the aggregated scoping options

If you want to get the aggregated scoping options of a chain of named scopes use ActiveRecord::Base.current_scoped_methods

It works in the fashion of:

Shirt.red.medium.alphabetical.current_scoped_methods
# ==>
{
  :create => {}, 
  :find => {
    :conditions => {:color => 'red', :size => 'medium'}, 
    :order => 'shirts.name ASC'
  } 
}
February 11, 2010
4 thanks

reload equivalent for models

The reset_column_information method provides a similar function for the model itself. Most useful during migrations.

January 30, 2010
3 thanks

Paying attention to query parameters

Standard action caching ignores query parameters, which means you’d get the same results for a URL with and without query parameters if it was action cached. You can make it pay attention to them by using a custom cache path like so:

caches_action :my_action, :cache_path => Proc.new { |c| c.params }

Or, maybe you want some of the query parameters, but not all to factor into different versions of that action’s cache:

:cache_path => Proc.new { |c| c.params.delete_if { |k,v| k.starts_with?('utm_') } }

Beware of things like pagination if you use expires_in to expire the cache, as pages could get out of sync.

January 21, 2010
3 thanks

W3CDTF Format

Here is the formatted string for the W3CDTF datetime format (http://www.w3.org/TR/NOTE-datetime). It has a semicolon in the timezone part, therefore you cannot use ‘%z’:

Time::DATE_FORMATS[:w3cdtf] = lambda { |time| time.strftime("%Y-%m-%dT%H:%M:%S#{time.formatted_offset}") }
January 20, 2010
4 thanks

Using html text instead of default response

If you have a string containing html and want to assert_select against it, as the doc states you have to pass in an element (HTML::Node) as the first argument. You can do something like this:

doc = HTML::Document.new('<p><span>example</span></p>')
assert_select doc.root, 'span'
January 20, 2010
3 thanks
January 16, 2010 - (>= v2.2.1)
7 thanks

Pretty way to test for current environment

You can check your current Rails environment using nice methods such as:

Rails.env.development?
Rails.env.test?
Rails.env.production?
Rails.env.your_custom_environment?
January 6, 2010
6 thanks

Doesn't return nil if the object you try from isn't nil.

Note that this doesn’t prevent a NoMethodError if you attempt to call a method that doesn’t exist on a valid object.

a = Article.new

a.try(:author) #=> #<Author ...>

nil.try(:doesnt_exist) #=> nil

a.try(:doesnt_exist) #=> NoMethodError: undefined method `doesnt_exist' for #<Article:0x106c7d5d8>

This is on Ruby 1.8.7 patchlevel 174

December 18, 2009
4 thanks

Version Ranges

To specify a version range, use array syntax like this:

config.gem 'paperclip', :version => ['>= 2.3.1.1', '< 3.0']

The example will, of course, match any version 2.3.1.1 or newer up until (not including) 3.0 or later.

November 12, 2009
8 thanks

Use hash form of updates argument

The examples are unfortunate, because passing a string as the updates argument is an invitation to SQL injection attacks. Don’t do this!

Billing.update_all("author='#{author}'")

Use the hash form of updates instead:

Billing.update_all(:author => author)

Then the SQL adapter will quote everything safely. Even if [you think] you’re sure there’s no quoting issue, it’s better to cultivate the habit of using the hash form just in case you missed something.

Same with conditions–use the hash or array form rather than a string if there are variables involved.

BTW, to do this and give options, of course you’ll need to put the braces back in:

Billing.update_all({:author => author},
                   ['title like ?', "#{prefix}%"])
November 5, 2009 - (>= v2.1.0)
7 thanks

Named scope better than conditions

In modern versions of Rails, in most cases a named_scope is a better alternative to using :conditions on your has_many relations. Compare:

class User
  has_many :published_posts, :conditions => {:published => true}
end
user.published_posts

with:

class Post
  named_scope :published, :conditions => {:published => true}
end
class User
  has_many :posts
end
user.posts.published

It’s better because the Post’s logic (“am I published?”) should not be coupled within User class. This makes it easier to refactor: e.g. if you wanted to refactor the boolean :published field into a :status field with more available values, you would not have to modify User class. Having to modify User when you refactor some implementation detail of Post class is clearly a code smell.

This also applies to :order, :group, :having and similar options.

October 30, 2009
7 thanks

How FormBuilders work

What, you were expecting documentation? :)

An excellent survey of how FormBuilders work is here:

http://code.alexreisner.com/articles/form-builders-in-rails.html

October 28, 2009
7 thanks

#blank?

The opposite of this is #blank?

October 27, 2009
4 thanks

#present?

The opposite of this is #present?

October 22, 2009 - (>= v2.1.0)
4 thanks

Update statement won't include all attributes with ActiveRecord::Dirty

With the addition of ActiveRecord::Dirty, the update statement will only feature changed columns, as opposed to the comment of railsmonk below.

October 15, 2009
4 thanks

Have check_box checked by default

In addition to comment below, you can make a column with default value so in your forms it will be enabled by default and behave correctly with validation errors unlike :checked => true

in your migration

add_column :accounts, :ssl_enabled, :boolean, :default => 1
October 7, 2009 - (>= v2.3.2)
3 thanks

Streaming XML with Builder

To generate larger XMLs, it’s a good idea to a) stream the XML and b) use Active Record batch finders.

Here’s one way of doing it:

def my_action
  @items = Enumerable::Enumerator.new(
    Item.some_named_scope,
    :find_each,
    :batch_size => 500)

  respond_to do |format|
    format.xml do
      render :text => lambda { |response, output|
        extend ApplicationHelper

        xml = Builder::XmlMarkup.new(
          :target => StreamingOutputWrapper.new(output),
          :indent => 2)
        eval(default_template.source, binding, default_template.path)
      }
    end
  end
end

The Builder template does not need to be modified.

October 2, 2009
4 thanks

form_tag with named route and html class

<% form_tag position_user_card_path(@user, card), :method => :put, :class => ‘position-form’ do %>

September 14, 2009
6 thanks

Pluralize Without Count

Helper method that returns the word without the count.

application_helper.rb

def pluralize_without_count(count, noun, text = nil)
  if count != 0
    count == 1 ? "#{noun}#{text}" : "#{noun.pluralize}#{text}"
  end
end

Example usage:

_form.html.erb

<%= pluralize_without_count(item.categories.count, 'Category', ':') %>
September 9, 2009
3 thanks

Will discard any order option

order_by(:created_at).find_each == FAIL!!!

class ActiveRecord::Base
  # normal find_each does not use given order but uses id asc
  def self.find_each_with_order(options={})
    raise "offset is not yet supported" if options[:offset]

    page = 1
    limit = options[:limit] || 1000

    loop do
      offset = (page-1) * limit
      batch = find(:all, options.merge(:limit=>limit, :offset=>offset))
      page += 1

      batch.each{|x| yield x }

      break if batch.size < limit
    end
  end
end
August 13, 2009 - (>= v2.3.2)
3 thanks

with_exclusive_scope example by Ramon broken in latest Rails

The example Ramon gave works within the model itself, i.e.

class Article
  def closed
    with_exclusive_scope { find(:all) }
  end
end

However, from what I can see, this approach does not work within a controller. You may be wanting to use

Article.with_exclusive_scope { find(:all) }  #=> "SELECT * FROM 'articles'

But it will error out about find(:all) not existing on ArticlesController. To get around this, you must now do

Article.with_exclusive_scope { Article.find(:all) }  #=> "SELECT * FROM 'articles'

In otherwards, find(:all) isn’t being executed in the scope of the model, but in the controller in which its called.

Took me a minute or two to find out, so I thought I’d let others know.