Ruby Hash: Convert String keys to Symbols

Ever had a hash which contained strings as keys and needed symbols instead? I do: From a REXML::Document I created a hash. Unfortunately, the keys were all strings and I needed them to be symbols at some other point in the app. Thank god, Ruby is capable of extending any object “on the fly”. So, I wrote a simple extension to Hash, which you might find useful as well:

class Hash
  #take keys of hash and transform those to a symbols
  def self.transform_keys_to_symbols(value)
    return value if not value.is_a?(Hash)
    hash = value.inject({}){|memo,(k,v)| memo[k.to_sym] = Hash.transform_keys_to_symbols(v); memo}
    return hash

Usage is:

a = { "key" => 123, "inner_hash" => { "another_key" => "blabla" }}
a = { :key => 123, :inner_hash => { :another_key => "blabla" }}

Passenger and OpenID

I recently updated Passenger 2.0.6 to 2.2.4 and experienced that openID logins were not working anymore. Seems like it tries to log output to some strange log location.

However: If anyone comes across the same problem: Simply add


to your environment.rb file and everything will work like a treat again.

Rails’ to_xml w/ multiple associations.

This is a pain and took me about an hour to figure out today.

Rails ActiveRecord instances offer a nice function to render xml:


This method can be fed with a parameter

:include => []

to have all associations being integrated in the XML tree, just like when calling

my_model = MyModel.find( :include => [association])

But when I tried to use it, it always failed when dealing with nested associations. Until I found out the trick.
This is how it works: Basically you need to build a list of nested hashes.

class Book < ActiveRecord::Base
  has_many :pages
  has_one :owner
class Owner < ActiveRecord::Base
  has_many :books
class Page < ActiveRecord::Base
  has_many :spots_of_coffees
  belongs_to :book
class SpotOfCoffee < ActiveRecord::Base
  belongs_to :page

Now, you want to create a nice XML output containing a book, with its owner, pages and all spots of coffee?
Pretty easy:

  @book = Book.first
  includes = {} # let's build a hash; it's easier to read. At least for me...
  includes[:owner] = {} # owner has no association. So, let's take an empty hash as target
  includes[:pages] = { :include => :spots_of_coffee } #load pages and include its spots of coffee
  respond_to do |format|
    format.xml  { render :text => @book.to_xml(:include => includes) }

Rails: Custom image sizes using has_attachment

Ever wanted to offer users the possibility to define their very own image sizes for uploaded pictures?

Here’s how you can quickly do that.

You will have a class acting as a an attachment such as:

class AssetImage < ActiveRecord::Base

has_attachment :content_type => :image,
:storage => :file_system,
:max_size => 1.megabytes,
:path_prefix => "public/system/images/#{ActiveRecord::Base.configurations[RAILS_ENV]['domain_name']}/assets/images",
:thumbnails => { :large => '450>', :normal => '300', :medium => '200', :thumbnail => [100,75] },
:processor => :rmagick



First add a cattr_accessor to store your custom size in the class:

cattr_accessor :custom_size

Now, add a before_save callback which takes the assigned value and adds it to the list of requested image sizes. It is using the value as a minimum size while keeping aspect ratio.

#store custom size
def before_save
  return if AssetImage.custom_size.nil?
  attachment_options[:thumbnails][:custom] = AssetImage.custom_size.to_s + ">"

In your controller do something like this: Take a value from your parameters and store it in your model to have your image customized.

def add_image
  AssetImage.custom_size = params[:custom_size].to_i.to_s rescue "100"
  a =[:asset_image])
  redirect_to :action => :index

Use ar_mailer for future mail delivery

This little howto describes, how to use ar_mailer to schedule emails for future delivery.

Sorry for the bad formatting. Might change it someday…
1) Migrate emails table and add needed fields

  add_column :emails, :various, :string #holds classname and id of any object you want to
  add_column :emails, :type, :string #type of email
  add_column :emails, :date_to_send, :date #date to send that mail

2) Override “def find” in email.rb

  def self.find(*args)
    with_scope(:find=>{ :conditions=>["(date_to_send IS NULL OR date_to_send <= ?)",] }) do

3) Create DelayedEmail class, inherting Email

  class DelayedEmail < Email
    before_save :set_due_date
    before_save :set_various_field
    @@days_before_sending = 21 #default is 3 weeks after creation of various object
    @@various_class = nil

    def set_due_date
      self.date_to_send = + @@days_before_sending

    def set_various_field
      name = @@various_class.class.to_s + "_" rescue "NOCLASS_"
      id = rescue "0"
      self.various = name + id

    #tell email to which object it belongs. might be important for future deletion of unsent mails
    def self.set_various_class(c)
      @@various_class = c

    #tell email how many days shall pass by before sending email
    def self.set_days(days)
      @@days_before_sending = days

4) Modify ar_mailer standard emailer class in controller before delivery and set it back afterwards

  #Let any mailer send an email through this class
  #eg. Mailer.deliver_mymail(...)