kinderman.net

If you use ActiveRecord observers in your application and are concerned about the isolation of your model unit tests, you probably want some way to disable/enable observers. Unfortunately, Rails doesn't provide an easy way to do this. So, here's some code I threw together a while ago to do just that.

module ObserverTestHelperMethods
  def observer_instances
    ActiveRecord::Base.observers.collect do |observer|
      observer_klass = \
        if observer.respond_to?(:to_sym)
          observer.to_s.camelize.constantize
        elsif observer.respond_to?(:instance)
          observer
        end
      observer_klass.instance
    end
  end

  def observed_classes(observer=nil)
    observed = Set.new
    (observer.nil? ? observer_instances : [observer]).each do |observer|
      observed += (observer.send(:observed_classes) + observer.send(:observed_subclasses))
    end
    observed
  end

  def observed_classes_and_their_observers
    observers_by_observed_class = {}
    observer_instances.each do |observer|
      observed_classes(observer).each do |observed_class|
        observers_by_observed_class[observed_class] ||= Set.new
        observers_by_observed_class[observed_class] << observer
      end
    end
    observers_by_observed_class
  end

  def disable_observers(options={})
    except = options[:except]
    observed_classes_and_their_observers.each do |observed_class, observers|
      observers.each do |observer|
        unless observer.class == except
          observed_class.delete_observer(observer)
        end
      end
    end
  end

  def enable_observers(options={})
    except = options[:except]
    observer_instances.each do |observer|
      unless observer.class == except
        observed_classes(observer).each do |observed_class|
          observer.send :add_observer!, observed_class
        end
      end
    end
  end
end

Include this in a Test::Unit::TestCase or 'include' in your RSpec configuration, whatever rocks your boat. Here's a stupid example:

class SomethingCoolTest < Test::Unit::TestCase
  include ObserverTestHelperMethods

  def setup
    disable_observers
  end

  def teardown
    enable_observers
  end

  def test_without_observers
    # ...
  end

end

When you go to test the behavior of the observer itself, simply disable/enable like the following to disable/enable all observers except the one you're testing:

class DispassionateObserverTest < Test::Unit::TestCase
  include ObserverTestHelperMethods

  def setup
    disable_observers :except => DispassionateObserver
  end

  def teardown
    enable_observers :except => DispassionateObserver
  end

  def test_without_observers_except_dispassionate_observer
    # ...
  end

end

In Rails, hooking up an ActiveRecord model to use a value object to aggregate over a set of database fields is a piece of cake. With the accessor methods that are created for a composed_of association, you can now deal exclusively with the composed_of field on your model, instead of directly manipulating or querying the individual database fields that it aggregates. Or can you? As long as all you're doing with the aggregate field is getting and setting its value, your aggregated database fields remain encapsulated. However, if you want to retrieve instances of your model from the database through a call to a finder method, you must do so on the individual database fields.

Consider the following ActiveRecord model definition:

class Customer < ActiveRecord::Base
  composed_of :balance, :class_name => "Money", :mapping => %w(balance_amount amount)
end

Given such a model, we can do something like this with no problem:

customer = Customer.new
customer.balance = Money.new(512.08)
customer.balance                      # returns #<Money:abc @amount=512.08>
customer.save!

However, now that we've saved the record, we might want to get that record back from the database at some point with code that looks something like:

customer = Customer.find(:all, :conditions => { :balance => Money.new(512.08) })

or like:

customer = Customer.find_all_by_balance( Money.new(512) )

This would provide full encapsulation of the aggregated database fields for the purposes of both record creation and retrieval. The problem is, at the time of my posting this article, it doesn't work. Instead, you have to do this:

customer = Customer.find(:all, :conditions => { :balance_amount => 512.08 })

To deal with this problem, I've submitted a ticket, which is currently scheduled to be available in Rails 2.1.

If you need this functionality, but your project is using a pre-2.1 release of Rails, I've also created a plugin version of the changes I submitted in the aforementioned ticket. To install:

script/plugin install http://svn.ryankinderman.net/find_conditions_with_aggregation

Addendum: The patch has been committed to changeset 8671. Yay!

Today, I was trying to get Selenium to click an anchor tag that was created with the "link" plugin in a TinyMCE editor. I was able to verify that the link was present with something as simple as verifyElementPresent('link=Link Text'). However, when I tried calling clickAndWait('link=Link Text'), it gave a "Window does not exist" error. A quick Google search yielded the answer: a bug in Selenium Core.

When the TinyMCE "link" plugin creates a link that doesn't open in a new window, it sets the "target" attribute on the anchor tag to "_self". Selenium Core versions prior to 0.8.4 (which hasn't been released yet) don't respond to links with "target" set to "_self".

If you're doing Rails development and using the selenium_on_rails plugin, it uses an old version of Selenium Core (0.7.something) as of this posting. To fix the anchor tag problem, I replaced the contents of the selenium-core directory under vendor/plugins/selenium_on_rails with that of the core directory of the Selenium Core 0.8.3 release, then applied the patch described in the bug spec linked to above. This seems to have fixed the problem.

Hopefully this saves you all some time and muddling.

A few weeks ago (okay, more than a few weeks ago, it took me a while to write this), I discussed the problems involved with passing nested hash parameters to named routes in Rails. My coding pair and I discovered another bug (still using rev 5522) when passing hash parameters to a named route in Rails, this time when the hash contains arrays. For example, consider the following call to a named route:

person_url(:name => ['Ryan', 'Kinderman'])

"http://someurl.com/people?name[]=Ryan&name[]=Kinderman"

"http://someurl.com/people?name=Ryan%2FKinderman"

person_url(:name => {0 => 'Ryan', 1 => 'Kinderman})

What I present here is a detailed explanation of the problem, with instructions at the end on how to install my plugin patch to fix it. My explanation and patch address the issues for both nested and array parameters. There are a number of methods involved in the solution to this problem. It may be useful at this point for you to refer to Jamis Buck's excellent articles on the gory details of Rails route recognition and generation.

The Rails methods involved in processing route parameters are listed below, in their general call sequence:

• ActionController::Base.url_for in action_controller/base.rb
OR
• ActionView::Helpers::UrlHelper#link_to in action_view/helpers/url_helper.rb
• RouteSet#generate in action_controller/routing.rb
• RouteSet#options_as_params in action_controller/routing.rb
• Array#to_param in active_support/core_ext/array/conversions.rb
• Route#generate in action_controller/routing.rb
• Route#write_generation in action_controller/routing.rb
• Route#append_query_string in action_controller/routing.rb
• Route#build_query_string in action_controller/routing.rb

The other specific issue lies in the Route#build_query_string method. Take a look at the method, and notice the part that looks like:

if value.class == Array
  key <<  '[]'
else    
  value = [ value ] 
end     

So, those are the issues involved in why array and nested hash parameters don't work properly in calls to url_for. Rather than going through my solution, I'm offering it as a Rails plugin with full unit test coverage, and plan to submit it as an actual patch to the Rails team, with the code cleaned up a bit more. Maybe there are reasons why this sort of thing isn't supported, but I can't think what they might be. I'll post updates here if and when I get more information on this. If you have comments or questions on this patch or parts of the code, please let me know.

You can install the Rails plugin by typing the following into your command-line: ruby script/plugin install http://svn.ryankinderman.net/nested_params_patch To see the issues I've discussed first-hand, after installing the plugin, take a look at controller_test.rb.

Addendum: I checked, and as of revision 6141 of Rails, the issues covered by this article are still present, and the plugin still fixes them.

Addendum (2007/04/03): I've just got around to confirming that, as rwd's commented, the bug has been fixed. If you're using revision 6343 or later of Rails, you probably aren't going to need this patch. Yay!

It's not a good idea to raise StandardError directly from your Rails application, particularly when using an exception as a way to indicate a recoverable error from an ActiveRecord transaction. In such cases, it's better to subclass from StandardError and raise the subclass instead. If you use StandardError directly, you may find that your system is catching and recovering from errors that are related to faulty logic rather than broken business rules.

For example, consider the following bad code:

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def some_method(x)
  x[x.length] + 1
  raise StandardError if x[0] < 2
end

begin
  a = [1, 2]
  some_method( a )
rescue StandardError
  puts "Bad value for index 0: #{a[0]}"
end

If you wrote a unit test for the some_method method, and asserted that StandardError was raised, it would pass incorrectly. This is especially misleading if you are writing a test for a controller action and asserting that, upon some error condition, the application redirects the user to a page displaying that error. I find that I don't explicitly raise many errors from my application code, except when I wrap the code in a controller action inside an ActiveRecord transaction. The only way to roll back the transaction is to raise an exception from within the transaction and rescue from it outside, such as:

class SomeController < ApplicationController
  def some_action
    begin
      SomeRecordClass.transaction do
        a = [1, 2]
        some_method( a )
      end
    rescue StandardError
      @error_message = "Bad value for index 0: #{a[0]}"
      render 'some_template'
      return
    end
    redirect_to some_url
  end
end

I've never (as of rev 5522) been able to pass a nested hash as parameters to url_for and have it flatten it properly on the generated URL. I encountered the problem again the other day and, having had just about enough, decided to try and nip it in the bud.

The problem I was having occurred when tried to make an HTTP request to a named route such as:

people_url(:person => { :name => 'Bob', :profession => 'Developer' })

When I've encountered this problem in the past, I could never find any information from someone who's actually solved the problem. There are a few patches submitted as tickets to the Rails devs, but one seems to be a duplicate of the other, and neither seems to fix this problem on Edge, at least not for my particular use case.

The root of this particular problem lies in a method in the action_controller/routing.rb file within actionpack/actioncontroller, in the options_as_params of the RoutingSet class. The method, without comments, looks like this:

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def options_as_params(options)
  options_as_params = options[:controller] ? { :action => "index" } : {}
  options.each do |k, value|
    options_as_params[k] = value.to_param
  end
  options_as_params
end

To solve this problem, I changed the method to look like this:

def options_as_params(options)
  options_as_params = options[:controller] ? { :action => "index" } : {}
  options.parameterize do |param_key, param_value|
    options_as_params[param_key] = param_value.to_param
  end
  options_as_params
end

{
  :person => {
    :name => 'Bob',
    :profession => 'Developer'
  }
}

{
  :'person[name]' => 'Bob',
  :'person[profession]' => 'Developer'
}

class Hash

  def flatten(superkey)
    flattened_hash = {}
    self.each do |key, value|
      flattened_hash["#{superkey}[#{key}]".to_sym] = value
    end
    flattened_hash
  end
  
  def parameterize
    self.each do |k, value|
      if value.is_a?(Hash)
        value.flatten(k).each { |fk, fv| yield fk, fv }
      else
        yield k, value
      end
    end       
  end

end