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Notes posted to Ruby on Rails

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July 28, 2009
8 thanks

Return True

As is the case with the before_validation and before_save callbacks, returning false will break the callback chain. For example, the expire_cache_id method will not run if Rails.cache.expire returns false (as it will if the key is not cached with memcache).

Returning False Example (Bad)

after_save :expire_cache_by_name
after_save :expire_cache_by_id

def expire_cache_by_name
  Rails.cache.expire("my_object:name:#{self.name}")
end

def expire_cache_by_id
  Rails.cache.expire("my_object:#{self.id}")
end

Returning True Example (Good)

def expire_cache_by_name
  Rails.cache.expire("my_object:name:#{self.name}")
  return true
end

def expire_cache_by_id
  Rails.cache.expire("my_object:#{self.id}")
  return true
end
July 27, 2009 - (>= v2.2.1)
3 thanks

Overriding default validation messages

Before Rails 2.2 you could globally customize the default validation error messages by changing AR::Base.default_error_messages. The messages have now been moved to i18n, so to customize them in 2.2 and up, just create a locales/ folder in your config/ folder, copy activerecord/lib/active_record/locale/en.yml (in Rails source) to config/locales/en.yml, and then change the strings inside. As szeryf indicated below, the strings of interest are activerecord.errors.messages.

July 24, 2009
1 thank

Instance method

Please note that this is an instance method, not a class method (which seemed more logical for me and took me a while to see what’s wrong). So, you call it like this:

User.new.from_json '{"id": 1, "name": "DHH"}' # RIGHT!

not like this:

User.from_json '{"id": 1, "name": "DHH"}' # WRONG!
July 23, 2009 - (v1.0.0 - v2.3.2)
0 thanks

Format meaning:

%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

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

%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)

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

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

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

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

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

%W - Week number of the current year, starting with the first Monday as the firstday 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 name

%% - Literal “%” character

July 23, 2009 - (v1.0.0 - v2.3.2)
7 thanks

Format meaning

%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

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

%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)

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

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

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

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

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

%W - Week number of the current year, starting with the first Monday as the firstday 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 name

%% - Literal “%” character

July 18, 2009
2 thanks

Sanitize in controllers, models, or libs -- *with* options

A Follow-up to k776’s note. If you want to specify tags or attributes, you should change your initializer to:

class String
  def sanitize(options={})
    ActionController::Base.helpers.sanitize(self, options)
  end
end

Then you can call it from any string like so:

'string'.sanitize(:tags => %w(table td tr), :attributes => %w(style id))
July 16, 2009
0 thanks

Also works with other markup

such as XML, not only HTML as suggested in the text.

July 15, 2009
0 thanks

Time.now in views.

Be careful if you use Time.now in views with time zone support enabled, as this will not actually do the time zone conversion.

Instead, use Time.zone.now.

July 8, 2009
0 thanks

Change Column. pt-br

Em sua migration escreva da seguinte forma:

Exemplo de uso.

def self.up
  change_column :sua_tabela, :seu_campo, :seu_tipo_campo
end
July 8, 2009
1 thank

Change Column.

Into your migration write the follow:

Using Exemple

def self.up
  change_column :yourtable, :your_field, :your_type_field
end
July 7, 2009 - (<= v2.3.2)
5 thanks

Options

Available options are (none of these exists by default):

* :limit - Requests a maximum column length. This is number of characters for :string and :text columns and number of bytes for :binary and :integer columns.
* :default - The column‘s default value. Use nil for NULL.
* :null - Allows or disallows NULL values in the column. This option could have been named :null_allowed.
* :precision - Specifies the precision for a :decimal column.
* :scale - Specifies the scale for a :decimal column.
July 7, 2009
0 thanks

Pretty Printing Routes

if you’d like to check out your routes in the console, you can do something like:

routes = ActionController::Routing::Routes

# which will return a RouteSet puts routes.routes

which’ll give you a nice output like: GET /messages/ {:action=>“index”, :controller=>“messages”} GET /messages.:format/ {:action=>“index”, :controller=>“messages”} POST /messages/ {:action=>“create”, :controller=>“messages”} POST /messages.:format/ {:action=>“create”, :controller=>“messages”} GET /messages/new/ {:action=>“new”, :controller=>“messages”} GET /messages/new.:format/ {:action=>“new”, :controller=>“messages”} GET /messages/:id/edit/ {:action=>“edit”, :controller=>“messages”} GET /messages/:id/edit.:format/ {:action=>“edit”, :controller=>“messages”} GET /messages/:id/ {:action=>“show”, :controller=>“messages”} GET /messages/:id.:format/ {:action=>“show”, :controller=>“messages”} PUT /messages/:id/ {:action=>“update”, :controller=>“messages”} PUT /messages/:id.:format/ {:action=>“update”, :controller=>“messages”} DELETE /messages/:id/ {:action=>“destroy”, :controller=>“messages”} DELETE /messages/:id.:format/ {:action=>“destroy”, :controller=>“messages”}

July 5, 2009
2 thanks

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

June 30, 2009
3 thanks

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

June 29, 2009
0 thanks

: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})
June 25, 2009
1 thank

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.

June 25, 2009 - (>= v2.3.2)
1 thank

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
June 22, 2009
3 thanks

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 %>
June 19, 2009
1 thank

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
June 19, 2009
2 thanks

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
June 18, 2009
3 thanks

Not really deprecated

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

June 18, 2009
11 thanks

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.

June 18, 2009
1 thank

Expensive method!

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

June 17, 2009
3 thanks

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
June 16, 2009
0 thanks

: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.

June 13, 2009 - (>= v2.3.2)
0 thanks
June 12, 2009
3 thanks

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

June 12, 2009
1 thank

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?
June 11, 2009
0 thanks

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
June 11, 2009
4 thanks

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, …)