Good notes posted to Ruby on Rails

Passing arguments to block

To pass arguments to block being captured, just list them as capture method params. I.e.

def export(exportable, export_klass, options={}, &block)
  result = ""
  #...
  if block_given?
    result += capture(my_custom_var_i_want_to_pass_to_block, &block)
  end
  result
end

Then simply…

 <%= export(@a, @b) do |my_custom_var| %>
  <% if my_custom_var.nil? %>
    My custom var is nil!!!
  <% end %>
<% end %>

case-insensitive uniqueness

For case-insensitive uniqueness:

validate :username, :uniqueness => {:case_sensitive => false}

Undocumented callbacks

Not sure why this isn’t documented… there are callbacks for before/after_add and before/after_remove. Example

has_many :things, :after_add => :set_things, :after_remove => :remove_things

def set_things(thing)
  ...
end
def remove_things(thing)
  ...
end

Disable STI

I had to add “self.inheritance_column” as opposed to simply “inheritance_column” to get this to work.

Code example

class MyModel < ActiveRecord::Base
  # disable STI
  self.inheritance_column = :_type_disabled
end

complex conditions

If you need add complex conditions you can use this:

Model.where(:foo => 'bar').where(:attr => 1).update_all("author = 'David'")

helpers using options for select

You can now add html options to select options by creating a container with items like the following:

Code Example

['display','value',:class => 'option_class']

This will produce:

Code Example

<option value="value" class="option_class">display</option>

link to nothing if link_to_if condition is false

When the link_to_if condition is false you can get this helper to display nothing by doing something like this

<%= link_to_if(message.user, 'Poster', message.user){} %>

^ That will display nothing if message.user does not exist.

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

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.

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.

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

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

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.

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.

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.

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

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

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.

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

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', '')

to set NULL => NO

use :null => false

change_column :my_table, :my_column, :integer, :default => 0, :null => false

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

Common use

I typically use require_dependency when developing a class or module that resides in my rails app, perhaps in the lib/ dir. A normal require statement does not reload my changes, so I use require_dependency in files that reference my newly developed class or module.

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

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 -%>

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.

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

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

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.

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