Notes posted to Ruby on Rails

To verify if the element exists before replacing.

Just add this code into a initializer file.

Atention: The code starts at the “module ActionView” and the last “end” has to be copied too.

module ActionView

module Helpers
  module PrototypeHelper
    class JavaScriptGenerator #:nodoc:
      module GeneratorMethods
        def replace_html_if_exists(id, *options_for_render)
          call "if($('#{id}')) Element.update", id, render(*options_for_render)
        end
      end
    end
  end
end

end

Be careful with name of attribute writer

If restricting access to attributes you normally get code like

attr_accessible :foo,  

When using these nested attributes you end up with code like

attr_accessible :foo, :bar_attributes

Its very easy to leave of the _attributes suffix e.g

attr_accessible :foo, :bar

which will cause you all sorts of problems

:selected

If you want some object to be selected by default, be sure to use its id, not the whole object.

 collection_select(:post, :author_id, Author.all, :id, :name_with_initial, {:selected => current_book.authors.map(&:id)})
#=> :selected => [1,2,3,4]

and not

collection_select(:post, :author_id, Author.all, :id, :name_with_initial, {:selected => current_book.authors})

Returns a copy of the attribute contents

As szeryf notes, this is a really expensive method, but another important remark is that the contents returned are a copy of the actual values.

model.attributes['name'] # => 'Joe'
model.attributes['name'] = 'Jim'
model.attributes['name'] # => 'Joe' still
model.name # => 'Joe'

This has the potential to be confusing as you’re given the impression you have direct access to the attributes.

Validate() is run always before one of the more specific validation methods

I did not see this mentioned explicitly anywhere.

The method validate is run always before a call to validate_on_create or validate_on_update is made.

Example:

class Foo < ActiveRecord::Base
  def validate
    puts 'In validate'
  end

  def validate_on_create
    puts 'In validate_on_create'
  end

  def validate_on_update
    puts 'In validate_on_update'
  end
end

Now, when creating a new Foo using script/console, the output is as follows:

In validate
In validate_on_create

and when updating a Foo, the output looks like:

In validate
In validate_on_update

Optional local assigns

When you have a partial with optional local assigns, for instance:

<%= render :partial => 'articles/preview' %>
<%= render :partial => 'articles/preview', :locals => { :show_call_out => true } %>

And you don’t want the partial to break when the local isn’t assigned, you can reference it through the local_assigns local variable instead of through the template binding:

<% if local_assigns[:show_call_out] %>
  <em><%= format @article.call_out %></em>
<% end %>

Usage example

class Aa

 class_inheritable_accessor :test
end
=> [:test]

Aa.test = 10
=> 10

Aa.test
=> 10

Bb = Class.new(Aa)
=> Bb

Bb.test
=> 10

Bb.test = 5
=> 5

Bb.test
=> 5

Aa.test
=> 10

Re: How to test different responses

In addition to using:

@request.accept = "text/javascript" #=> request JS

as rubymaverick and nachocab suggested, you can also pass :format when calling your action, eg:

it "GET #most_viewed renders #most_viewed.js.rjs template if js requested" do
  get :most_viewed, :format => 'js'
  response.should render_template('most_viewed')
end

Not really deprecated

This isn’t really deprecated, it’s just relocated to ActiveRecord::AttributeMethods#read_attribute

Important note

It has been said that “it can be compared to, but isn’t the same thing as”:

class Bar
  class << self
    attr_accessor :greeting
  end
end

Which is true. However, they are “inherited” isn’t exactly the case. Rather, cattr_accessor uses class variables.

The problem with class variables in Ruby, is that a class variable is the same object across all subclasses of a class. Consider the following example of what happens with cattr_accessor:

class A
  @@foo = 'foo'

  def self.foo
    @@foo
  end
end

p A.foo # => "foo"

class B < A
end

p B.foo # => "foo"

class B
  @@foo = 'bar'
end

p B.foo # => "bar"

So far so good you might think. However, something you might not have expected is that the variable has now also changed in class A:

p A.foo # => "bar"

This is in my opinion almost never what you’d want. More probable is that you’d want the individual class instance to have an accessor. (Remember classes are objects in Ruby). I do the following in regular Ruby:

class A
  class << self
    attr_accessor :foo
  end

  self.foo = 'foo'
end

p A.foo # => "foo"

class B < A
end

p B.foo # => nil

class B
  self.foo = 'bar'
end

p B.foo # => "bar"

p A.foo # => "foo"

As you can see, this returns nil when a value hasn’t explicitly been set yet on the new class instance. If you’d like to have inheritance without messing with the superclasses variables, have a look at ActiveSupport’s class_inheritable_accessor, which does the same as I just explained, but creates a clone of the object and assigns it to the subclass whenever a class is inherited.

What I’d normally do in Ruby to fix the issue of it returning nil is to create the accessor manually and have it set the instance variable to the default if it’s nil:

class A
  class << self
    def foo
      @foo ||= 'foo'
    end
  end
end

class B < A
end

p B.foo # => nil

So to recap:

• cattr_accessor uses class variables (@@foo), in which case the object is shared across all subclasses of a class. Use it mainly for static data, in which case you’d probably best use a constant.

• class_inheritable_accessor (or what I showed) uses instance variables (@foo) at the Class instance level. These variables are not shared across all subclasses.

Expensive method!

This method builds the a new hash every time it’s called, so be cautious not to use it in loops etc.

Skipping validation

Unlike the save method, you can’t pass false to update_attributes to tell it to skip validation. Should you wish to do this (consider carefully if this is wise) update the attributes explicitly then call save and pass false:

@model_name.attributes = params[:model_name]
@model_name.save false

:discard_month implicitly sets :discard_day to true

This may not be the behaviour that you want, and setting :discard_day => false doesn’t change this. One way of getting around this is to hide the month field using CSS e.g.

#some_date_field_2i {
  display:none;
}

If you use the :default option for the date_select, the correct default month will be passed through to the controller. Using this with :discard_year will give you a dropdown with only the day, but preserve the month and year as provided by :default.

Requirements for extra parameters not working

nm. just delete this entry

cattr_accessor_with_default

Class attribute assessors are neat if you want to set up modifiable constant-like varibles. This is how you’d normally set it up:

module MyPlugin
  class Conf
    @@awesome_level = 'huge'
    cattr_accessor :awesome_level
  end
end

Then you can call and modify it like this:

>> MyPlugin::Conf.awesome_level
=> 'huge'
>> MyPlugin::Conf.awesome_level = 'massive'
>> MyPlugin::Conf.awesome_level
=> 'massive'

If you have a pile of those accessors I’d do something like this (there might be a better way, but it works):

module MyPlugin
  class Conf
    def self.cattr_accessor_with_default(name, value = nil)
      cattr_accessor name
      self.send("#{name}=", value) if value
    end

    cattr_accessor_with_default :awesome_level, 'huge'
    cattr_accessor_with_default :speed_level, 'insane'
    cattr_accessor_with_default :indifferent_level
    cattr_accessor_with_default :craziness_level, 'nuts'
  end
end

This way you declare accessor and it’s optional default value on the same line

Conditions work for lower-level validate methods too

I don’t think this is mentioned in the docs anywhere, or else I couldn’t find it: Because validate, validate_on_create, and validate_on_update are ActiveSupport::Callbacks, their symbol forms support conditions just like validates_presence_of and company:

validate :permaname_must_be_unique, :if => :normal_entry?
validate_on_create :posted_at_must_be_valid_timestamp, :unless => Proc.new {|e| e.posted_at.nil? }
validate_on_update :title_must_not_contain_apostrophes, :if => :title_starts_with_a_b?

Not really helpful

When you’re trying to construct a specialized path name for a partial based on a record type you’re probably better off writing your own helper.

def topic_partial_path(topic)
  ['admin', topic.class.table_name, "#{topic.class.table_name.singularize}_as_topic"].join('/')
end

Keeping the flash object on multiple redirects

If your controllers are redirecting more than once, the flash contents will be lost. To avoid it, execute flash.keep before each redirection.

Check ActionController::Flash::FlashHash for more handy methods (discard, now, …)

If you want to do a find without the default scope...

Checkout with_exclusive_scope

How to use with exclusive scope

Code example

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

from http://ryandaigle.com/articles/2008/11/18/what-s-new-in-edge-rails-default-scoping

[:a, :b, :c].try([1]) ? The answer is No.

Correct way is this:

[:a, :b, :c].try(:at, 1)

Have the check_box checked by default

To have the check box checked by default, pass either :checked => true or :checked => 'checked' in the options. See ActionView::Helpers::InstanceTag#to_check_box_tag for details.

You're probably looking for the docs here

ActionController::Caching::Sweeping

This is ON by default in :has_many

When defining a has_many relationship this behaviour is on by default. See has_many documentation, look for the :validate flag.

add index with :quiet=>true option for indices that are possibly already added

# Allows you to specify indices to add in a migration that will only be created if they do not # already exist, or to remove indices only if they already exist with :quiet=>true module ActiveRecord::ConnectionAdapters::SchemaStatements

def add_index_with_quiet(table_name, column_names, options = {})
  quiet = options.delete(:quiet)
  add_index_without_quiet table_name, column_names, options
rescue
  raise unless quiet and $!.message =~ /^Mysql::Error: Duplicate key name/i
  puts "Failed to create index #{table_name} #{column_names.inspect} #{options.inspect}"
end
alias_method_chain :add_index, :quiet

def remove_index_with_quiet(table_name, column_names, options = {})
  quiet = options.delete(:quiet)
  raise "no options allowed for remove_index, except quiet with this hack #{__FILE__}:#{__LINE__}" unless options.empty?
  remove_index_without_quiet table_name, column_names
rescue
  raise unless quiet and $!.message =~ /^Mysql::Error: Can't DROP/i
  puts "Failed to drop index #{table_name} #{column_names.inspect}"
end
alias_method_chain :remove_index, :quiet

end

A catch-all format

If you’d like to specify a respond_to only for 1 or a few formats and render something else for all other formats, eg: (action.rss returns a feed but action.html or action.js should just render 404), use format.all:

respond_to do |format|
  format.rss { render_rss }
  format.all { render_404 }
end

Rails will render an empty string for all formats that don’t specify a response explicitly.

example

Ruby style

Dir[File.join(RAILS_ROOT, 'vendor', 'plugins', '*')]

Rails style

Dir[Rails.root.join('vendor', 'plugins', '*')]

Security hole in 2.3.2

This method has a security hole in Rails 2.3.2. See http://weblog.rubyonrails.org/2009/6/3/security-problem-with-authenticate_with_http_digest for explanation.

Rails 2.3.3 should fix the problem.

ActiveRecord::RecordNotSaved can be triggered by accidental false return values in callbacks

You may have this exception raised if any of the defined callbacks such as ActiveRecord::Base#before_save or ActiveRecord::Base#before_create return false.

This can happen accidentally. For example:

class MyModel < ActiveRecord::Base
  before_save :assign_default_foo

protected
  def assign_default_foo
    self.foo = false
  end
end

Since assign_default_foo leaves a false value on the stack, the model will not be saved. A way around this is to simply leave nil or an empty return instead:

class MyModel < ActiveRecord::Base
  before_save :assign_default_foo

protected
  def assign_default_foo
    self.foo = false
    nil
  end
end

Writing and reading a cookie in the same request.

As of 0349278f3da9f7f532330cf295eed35ede3bae66 cookie updates will persist in the current request.