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October 26, 2010
3 thanks

Polymorphic has_many within inherited class gotcha

Given I have following classes

class User < ActiveRecord::Base
end

class ::User::Agent < ::User
 has_many :leads,  :as => :creator
end

I would expect, that running

User::Agent.first.leads

will result in following query

SELECT "leads".* FROM "leads" WHERE ("leads".creator_id = 6 AND "leads".creator_type = 'User::Agent')

however it results in

SELECT "leads".* FROM "leads" WHERE ("leads".creator_id = 6 AND "leads".creator_type = 'User')

Possible solutions:

  • Make User class use STI - polymorphic relations will then retrieve correct class from :type field (however in my situation it was not an option)

  • If You do never instantiate User class itself, mark it as abstract

class User < ActiveRecord::Base
 self.abstract_class = true
end
  • If You do instantiate User class, as last resort You can overwrite base_class for User::Agent

class ::User::Agent < ::User
 has_many :leads,  :as => :creator

 def self.base_class
  self
 end
end
  • If none of above is an option and You do not care that You will lose some of relation’s features, You can always

class User::Agent < ::User
 has_many :leads,
          :as => :creator,
          :finder_sql => %q(SELECT "leads".* FROM "leads" WHERE ("leads".creator_id = #{id} AND "leads".creator_type = 'User::Agent'))
end
October 26, 2010
3 thanks

null to no effects

change_column will not query to replace the null values when you change null to false, even if you have a default set. This may cause the query to fail (may depend on the database used).

change_column_null will optionally take a value to replace nulls if you are setting null to false. If you want to set a default and disallow nulls you likely can’t do both in one change_column call.

October 20, 2010
6 thanks

use raw() instead

Don’t use this method unless you’re sure your string isn’t nil. Instead use the raw() method, which wont raise an exception on nil.

October 16, 2010 - (>= v3.0.0)
11 thanks

needs to be paired with respond_to

Needs to be paired with respond_to at the top of your class.

class MyController < ApplicationController
  respond_to :js, :html
October 13, 2010
12 thanks

Sending array parameters

Another technique to use when you need to send an array parameter is pass in the :multiple option.

check_box("puppy", "commands", {:multiple => true}, "sit", nil)
check_box("puppy", "commands", {:multiple => true}, "fetch", nil)
check_box("puppy", "commands", {:multiple => true}, "roll_over", nil)

If all checkboxes are checked, the paramters will be:

"puppy" => {"commands" => ["sit", "fetch", "roll_over"]}

NOTE: because of the gotcha, the hidden fields will be inserted and any unchecked boxes will be sent as “” (empty string). You will need to filter those values out in your model:

class Dog < ActiveRecord::Base
  def commands=(commands)
    commands.reject(&:blank?)
  end
end
October 9, 2010
6 thanks

Be Advised

Also may convert original string into Jamaican.

e.g.

"green moon".squeeze  #=> "gren mon"
August 25, 2010 - (>= v2.3.8)
9 thanks

Undocumented :inverse_of option

Support for the :inverse_of option was backported to 2.3.6+.

Here’s the description from the original commit: http://github.com/rails/rails/commit/ccea98389abbf150b886c9f964b1def47f00f237


You can now add an :inverse_of option to has_one, has_many and belongs_to associations. This is best described with an example:

class Man < ActiveRecord::Base
  has_one :face, :inverse_of => :man
end

class Face < ActiveRecord::Base
  belongs_to :man, :inverse_of => :face
end

m = Man.first
f = m.face

Without :inverse_of m and f.man would be different instances of the same object (f.man being pulled from the database again). With these new :inverse_of options m and f.man are the same in memory instance.

Currently :inverse_of supports has_one and has_many (but not the :through variants) associations. It also supplies inverse support for belongs_to associations where the inverse is a has_one and it’s not a polymorphic.

August 25, 2010 - (>= v2.3.8)
7 thanks

Undocumented :inverse_of option

Support for the :inverse_of option was backported to 2.3.6+.

Here’s the description from the original commit: http://github.com/rails/rails/commit/ccea98389abbf150b886c9f964b1def47f00f237


You can now add an :inverse_of option to has_one, has_many and belongs_to associations. This is best described with an example:

class Man < ActiveRecord::Base
  has_one :face, :inverse_of => :man
end

class Face < ActiveRecord::Base
  belongs_to :man, :inverse_of => :face
end

m = Man.first
f = m.face

Without :inverse_of m and f.man would be different instances of the same object (f.man being pulled from the database again). With these new :inverse_of options m and f.man are the same in memory instance.

Currently :inverse_of supports has_one and has_many (but not the :through variants) associations. It also supplies inverse support for belongs_to associations where the inverse is a has_one and it’s not a polymorphic.

August 25, 2010 - (>= v2.3.8)
3 thanks

Validating presence of parent in child

When creating a parent and its children using nested attributes, you can use the :inverse_of option on the association to correctly set the parent back references:

class Parent < ActiveRecord::Base
  has_many :children, :inverse_of => :parent
  accepts_nested_attributes_for :children
end

class Child < ActiveRecord::Base
  belongs_to :parent
  validates_presence_of :parent
end
August 13, 2010
10 thanks

add_to_base in Rails 3

use

model_instance.errors[:base] << "Msg" 

instead of depracated

model_instance.errors.add_to_base("Msg")

for Rails 3

August 11, 2010
3 thanks

In Rails3 use "unscoped" instead

The with_exclusive_scope examples no longer work in Rails3 because with_exclusive_scope is now a protected method which can and should not be used in a controller. Use the new unscoped method instead:

Article.unscoped

For mor details and examples have a look at: http://github.com/rails/rails/commit/bd1666ad1de88598ed6f04ceffb8488a77be4385.

July 29, 2010
4 thanks

Getting (n..end) reloaded

You can do

array[n..-1]
July 23, 2010
3 thanks

Moved in Rails 3

In Rails 3, this has moved to ActionDispatch::TestProcess

(Which means, if you want to use it in a test, you need to add the following to test_helper.rb:)

include ActionDispatch::TestProcess
July 20, 2010
3 thanks

When scripts don't end in .js

For example, Google Custom Search’s URL is http://www.google.com/jsapi

It’s an ugly hack, but works:

= javascript_include_tag('http://www.google.com/jsapi').sub('.js', '')
July 16, 2010
3 thanks

to set NULL => NO

use :null => false

change_column :my_table, :my_column, :integer, :default => 0, :null => false
July 14, 2010
6 thanks

uniqueness

You can scope uniqueness as well

validates :user_name, :presence => true, :uniqueness => {:scope => :account_id}

# the old way  
validates_uniqueness_of :user_name, :scope => :account_id
June 18, 2010
8 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 16, 2010
5 thanks

Require file from the same folder

If you want to require file from the same folder, the simplest way is

require File.expand_path('../file-to-require', __FILE__)

If your file is /lib/book.rb

File.expand_path('../page', '/lib/book.rb') => '/lib/page.rb'
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.

April 1, 2010
3 thanks

Doesn't return nil on empty array when param is given

This does not return nil if the array is empty and n is given.

[].shift(2) # => []

a = []
a.shift(2) # => []
a # => []
March 31, 2010
3 thanks

Interpolating

Note that to interpolate, the sequences must be inside single quotes:

# replace /ll/ with itself
'hello'.gsub(/ll/, '\0') # returns 'hello'
'hello'.gsub(/ll/, "\0") # returns 'he\000o'
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 12, 2010
3 thanks

Complete Formatting Codes

NOTE: Some of these seem only to work for DateTime (e.g. %L, %N)

%a - The abbreviated weekday name (“Sun”)

%A - The full weekday name (“Sunday”)

%b - The abbreviated month name (“Jan”)

%B - The full month name (“January”)

%c - The preferred local date and time representation

%C - Century (20 in 2009)

%d - Day of the month (01..31)

%D - Date (%m/%d/%y)

%e - Day of the month, blank-padded ( 1..31)

%F - Equivalent to %Y-%m-%d (the ISO 8601 date format)

%h - Equivalent to %b

%H - Hour of the day, 24-hour clock (00..23)

%I - Hour of the day, 12-hour clock (01..12)

%j - Day of the year (001..366)

%k - hour, 24-hour clock, blank-padded ( 0..23)

%l - hour, 12-hour clock, blank-padded ( 0..12)

%L - Millisecond of the second (000..999)

%m - Month of the year (01..12)

%M - Minute of the hour (00..59)

%n - Newline (n)

%N - Fractional seconds digits, default is 9 digits (nanosecond)

  • %3N millisecond (3 digits)

  • %6N microsecond (6 digits)

  • %9N nanosecond (9 digits)

%p - Meridian indicator (“AM” or “PM”)

%P - Meridian indicator (“am” or “pm”)

%r - time, 12-hour (same as %I:%M:%S %p)

%R - time, 24-hour (%H:%M)

%s - Number of seconds since 1970-01-01 00:00:00 UTC.

%S - Second of the minute (00..60)

%t - Tab character (t)

%T - time, 24-hour (%H:%M:%S)

%u - Day of the week as a decimal, Monday being 1. (1..7)

%U - Week number of the current year, starting with the first Sunday as the first day of the first week (00..53)

%v - VMS date (%e-%b-%Y)

%V - Week number of year according to ISO 8601 (01..53)

%W - Week number of the current year, starting with the first Monday as the first day of the first week (00..53)

%w - Day of the week (Sunday is 0, 0..6)

%x - Preferred representation for the date alone, no time

%X - Preferred representation for the time alone, no date

%y - Year without a century (00..99)

%Y - Year with century

%z - Time zone as hour offset from UTC (e.g. +0900)

%Z - Time zone name

%% - Literal “%” character

t = Time.now                        #=> 2007-11-19 08:37:48 -0600
t.strftime("Printed on %m/%d/%Y")   #=> "Printed on 11/19/2007"
t.strftime("at %I:%M%p")            #=> "at 08:37AM"
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 - (>= 1.2.8)
5 thanks

stub_chain is very useful when testing controller code

or any other chained method call type that you’d like to stub, example:

in your controller:

def new
  @user = current_site.users.new
end

in your spec:

it "#new should assign a @user" do 
  u = mock("User")
  controller.stub_chain(:current_site, :users, :new).and_return(u)
  assigns[:user].should == u
end

whereas before you had to stub each chained method call separately:

it "#new should assign a @user" do 
  u = mock("User")
  users = mock("Users collection", :new => u)
  site = mock("Site", :users => users)
  controller.stub!(:current_site).and_return(site)
  assigns[:user].should == u
end

Please note that stub_chain was added to RSpec in version 1.2.6

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.

March 3, 2010
3 thanks

Deprecated in 1.9.x!

Use FileUtils::copy instead. It is also in 1.8.x, FileUtils, so call that one instead.

March 3, 2010 - (>= v1_8_6_287)
4 thanks

makedirs(path) to create file path

mkdir will only create a single directory on an existing path. If you want to create a full path, like the `mkdir -p /full/path` command, use the makedirs method.

1.8: File.makedirs(path) 1.9: FileUtils.makedirs(path)

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