Notes posted to Ruby on Rails

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May 31, 2013
2 thanks

Do not mistakenly use serialize like other similar directives - attr_accessible, attr_accessor

serialize seems very similar to other directives that work on attributes such as attr_accessible. One may mistakenly assume that serialize can take a list of attributes. For eg:

class Tuk < ActiveRecord::Base
  attr_accessible :foo, :bar
  serialize :foo, :bar

This may lead to a cryptic error. Eg.

puts !Tuk.first.foo.nil?


NoMethodError at /file:location undefined method `new' for :bar:Symbol

This is because it tries to parse the YAML string stored in foo as an instance of :bar.

May 30, 2013
1 thank

Avoiding to_param method when using URL helper methods

I recently found myself in the situation where I needed to generate URLs which included the ID instead of the value returned from the model’s to_param method (since someone had overridden the to_param method). It turned out to be easier than I thought. You can simply pass an ID to the helper method and it will construct the URL correctly:

# /admin/foobars/123/edit
May 23, 2013 - (v3.0.0 - v3.2.13)
0 thanks

Use @output_buffer to set the context.

You can use assert_select to test helpers, just have to set the @output_buffer before you do.

Code example

class CurrencyHelperTest < ActionView::TestCase

  setup do
    # can use helper methods here
    @output_buffer = currency 54.78

  test 'currency use a div' do
    asert_select 'div'

May 23, 2013
0 thanks

A simple usage example

See http://apidock.com/rails/String/inquiry

env = "production".inquiry
env.production?  # => true
env.development? # => false
May 18, 2013
0 thanks

:include is also valid option

my_company.serializable_hash(:include => [:people])

May 15, 2013
0 thanks
April 27, 2013 - (v3.1.0 - v3.2.13)
4 thanks
April 10, 2013 - (v3.2.1 - v3.2.13)
2 thanks

be aware that this writes to tmp/cache

Its supposed to be http caching, but Rails will actually cache the response to whatever you specified as the cache store, *as well*, but only if you specify :public => true. The default is filestore so it will try to write to tmp/cache.

Only a problem if you don’t have the proper permissions set, in that scenario your apache/nginx logs could fill up very quickly with “permission denied errors”

Full explanation is here http://blog.tonycode.com/archives/418

April 4, 2013 - (>= v1.0.0)
0 thanks

increment_by_sql for PG

Note, if you’re using the code below for incrementing by SQL with a Postgres database, it’s not going to like the backticks. Just remove them:

def increment_with_sql!(attribute, by = 1)
  raise ArgumentError("Invalid attribute: #{attribute}") unless attribute_names.include?(attribute.to_s)
  original_value_sql = "CASE WHEN #{attribute} IS NULL THEN 0 ELSE #{attribute} END"
  self.class.update_all("#{attribute} = #{original_value_sql} + #{by.to_i}", "id = #{id}")
April 2, 2013 - (v3.0.0 - v3.2.13)
0 thanks

Use concat insted of joining collection explicitely

concat method will be useful to join the collection object from looping conditions.

arr = ["a", "b", "c"]
content_tag(:ul, :class => 'a class') do
  arr.each do |item|
  concat content_tag(:li, item)

And this will generate the html as shown below

<ul class="a class">
March 29, 2013
0 thanks
March 29, 2013
0 thanks

Edge case

Have look how #between? handle adge case. It’s different from DateTime’s.

Date.yesterday.between?(Date.yesterday, Date.tomorrow)
=> true

Date.tomorrow.between?(Date.yesterday, Date.tomorrow)
=> true
March 27, 2013 - (>= v3.0.0)
0 thanks

When dealing with has_many through

The non-repeating primary key id must be used with find_in_batches.

  • User has many things

  • User has many socks through things

  • Sock has many things

  • Sock has many users through things

For the sake of argument, assume the first user has two socks and all other users have one sock. There are 1000 users in total and 1001 socks in total.

=> 1001
agg = []
# Incorrect
User.joins(:socks).find_in_batches{|g| agg += g}
=> 1000

=> 1001
agg = []
# Correct
Sock.joins(:users).find_in_batches{|g| agg += g}
=> 1001
March 27, 2013 - (v3.0.0 - v3.2.13)
0 thanks
March 18, 2013
4 thanks

Beware - May cause performance issues

A serialized attribute will always be updated during save, even if it was not changed. (A rails 3 commit explains why: http://github.com/rails/rails/issues/8328#issuecomment-10756812)

Guard save calls with a changed? check to prevent issues.

class Product < ActiveRecord::Base
  serialize :product_data


product = Product.first


product = Product.first
product.save if product.changed?
March 5, 2013 - (v3.0.0 - v3.2.8)
0 thanks

Exceptions raised within are ignored.

From http://guides.rubyonrails.org/active_record_validations_callbacks.html

The after_commit and after_rollback callbacks are guaranteed to be called for all models created, updated, or destroyed within a transaction block. If any exceptions are raised within one of these callbacks, they will be ignored so that they don’t interfere with the other callbacks. As such, if your callback code could raise an exception, you’ll need to rescue it and handle it appropriately within the callback.

March 1, 2013
0 thanks

Default field order

If you want to set an app wide default order for the fields (rather than passing :order each time), use the locale file.

eg. edit config/locale/en.yml to include:

      - :day
      - :month
      - :year
February 22, 2013
0 thanks

Checking content_for

There’s a much simpler way to check if content exists or not, and it’s been provided as example in docs since 05.2010:

module StorageHelper
  def stored_content
    content_for(:storage) || "Your storage is empty"

But this behavior was broken with SafeBuffer. You’ll be able to use it again when this issue (github.com/rails/rails/issues/9360) will be fixed and merged with master.

February 20, 2013
0 thanks

It also works with strings

It works with strings:

ActiveRecord::Base.connection.column_exists?('users', 'id')

Which is helpful if you need to specify the database/schema to use:

ActiveRecord::Base.connection.column_exists?('secondary.users', 'id')
February 14, 2013 - (>= v3.2.8)
1 thank

conditional rescue from does not seem working on Rails 3.2.11

Be careful, conditional rescue_from does not work in Rails 3.2.11

February 8, 2013 - (>= v2.3.8)
0 thanks

The purpose of this method

This method keeps track of whether a hidden id field needs to be created when the form builder is generating fields for a nested model. It gets set to true by #hidden_field when that method is used to create a field named ‘id’.

Here’s an example of what this can be useful for: http://railsforum.com/viewtopic.php?id=39640

February 4, 2013
0 thanks

Your scope cannot be called &#x27;locked&#x27;

will cause intermittent problems of the type

undefined method 'locked' for #<Class:0x007fdab3025298>

Use something like ‘access_locked’ instead

February 2, 2013
0 thanks

Other Example


class Exam
 cattr_reader :code, :description, :points, :instance_reader => false

 @@code = "EXM"
 @@description = "Sent Exam"
 @@points = 1000

In this case it’s possible to use

Exam.code # => EXM
Exam.description # => Sent Exam
Exam.points # => 1000
January 29, 2013
0 thanks

Works also with Mongoid

What works for Active Record, also works for Mongoid:

        explanation: Description
January 26, 2013 - (v3.0.0 - v3.2.8)
0 thanks

Use sqlite3, not sqlite

Note that typically if you want to connect to an SQLite database the adapter would be “sqlite3”; not “sqlite” as depicted in the documentation above. Just using the term “sqlite” might result in the error message: “database configuration specifies nonexistent sqlite adapter”

January 23, 2013 - (>= v3.0.0)
1 thank

Using an unobtrusive Ajax (UJS) :onchange call to the controller#action

An :onchange call can be made using the Rails 3 jquery-ujs helper in the form:

check_box_tag( name, value, checked, html_and_other_options)

For example:

select_tag( "my_tag_id", entity.id,
  class: "progress bar update_msg", disabled: disabled?
  data: {
    remote: true,
    url: url_for( action: :my_controller_action, id: my_id)
    // application symbols
    progress_bar: "progress_bar_div_id",
    update: "message_div_id"

The jquery_ujs looks for data-remote and data-url. These can be spelled-out or placed in the data hash. The url must be formed as select_tag does not call url_for, unlike some of the other related tags. Values for application symbols can also be passed through. jQuery triggers will work on the Ajax events that occur. This generates the following:

<input class="progress_bar update_msg" data-progress-bar="progress_bar_div_id" data-remote="true" data-update="message_div_id" data-url="/my_controller/my_controller_action/my_id" id="my_tag_id" name="my_tag_id" type="checkbox" value="4"/>

In this example, by tying into the events the program makes visible an existing hidden progress bar while awaiting a server response, and then displays a div containing a message returned by the server and hides the progress bar. If the div contains a class= for notice or error, then they will fade out.

  .on('ajax:beforeSend', ".progress_bar", function(){ 
    // get id of element to make visible
    var progress_bar_id = '#' + this.getAttribute('data-progress-bar');
  .on('ajax:complete', ".progress_bar", function(){ 
    // get id of element to hide
    var progress_bar_id = '#' + this.getAttribute('data-progress-bar');
  .on('ajax:complete', ".update_msg", function(evt, xhr, options){ 
    // get id of element to contain message
    var update = this.getAttribute('data-update'); 
    $("#" + update).replaceWith($(xhr.responseText).attr("id", update));
    // cause responses with these classes to fade away...
January 21, 2013 - (v3.0.0 - v3.0.9)
0 thanks

for rails >= 3

template_root= is deprecated, use prepend_view_path instead

source: ActionMailer/DeprecatedApi/ClassMethods/template_root

January 18, 2013
0 thanks

Some documentation available in RailsGuides

The Rails engines getting started guide discusses the usage of isolate_namespace: http://edgeguides.rubyonrails.org/engines.html

January 8, 2013 - (v3.0.0 - v3.2.8)
0 thanks

Minor edit of pluralize_without_count

patrickberkeley’s method works great. I corrected the grammar a bit for inflection (the singular error).


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

This should work in much older versions of Rails also.

January 8, 2013
1 thank

Helper Methods inside of a Controller

When needing to include a helper method inside of a controller, instead of including the ENTIRE helper module, simply use this method like so:

module ApplicationHelper
  def fancy_helper(str)

class MyController < ApplicationController
   def index
     @title = view_context.fancy_helper "dogs are awesome"