Good notes posted to Ruby on Rails

Documentation

This method only returns a cache manager object of sorts, to see what you can do with it, see ActiveSupport::Cache::Store.

Documentation bug

When adding the :target option, the documentation states that you should user :href_options like so:

auto_link(post_body, :href_options => { :target => '_blank' })

However, I could only get it to work using :html instead:

auto_link(post_body, :html => { :target => '_blank' })

I’m using Rails 2.2.2, but I believe that this also happens for more recent version .

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

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.

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

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.

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

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 %>

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

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

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

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.

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.

Tip: Define from_param(...) as Opposite

Often when defining a to_param method, it’s handy to introduce an opposite method for decoding them. For example:

class User < ActiveRecord::Base
  def self.from_param(param)
    find_by_name!(param)
  end

  def to_param
    name
  end
end

While you can just as easily redefine the find() method, this may be confusing since the expectation is that find() works with numerical IDs, or whatever the key column is defined as.

A very thorough explanation of use

Ryan Daigle has a great article about 2.3’s new nest forms which does a really good job of explaining how to use this and some of the potential gotchas. Highly recommended:

http://ryandaigle.com/articles/2009/2/1/what-s-new-in-edge-rails-nested-attributes

Set :use_route to nil to let Rails pick the best route

Imagine the following case. You have two landing pages, one generic one, and an account specific one. The urls are as follows:

map.landing 'landing', :controller => 'landing', :action => 'index'
map.account_landing 'accounts/:account_id/landing', :controller => 'landing', :action => 'index'

Now imagine you want a path to the landing page, using the most specific route possible. If you have an account_id, use it, if not, skip it.

You could do

url_for(:controller => 'landing', :action => 'index', :account_id => current_account)

If current_account is set you’ll get “/accounts/:account_id/landing” if not, you’ll get “/landing”. However, that just looks ugly.

Enter :use_route => nil.

landing_path(:account_id => nil)                    # => '/landing'
landing_path(:account_id => 1)                      # => '/landing?account_id=1'
landing_path(:account_id => nil, :use_route => nil) # => '/landing'
landing_path(:account_id => 1, :use_route => nil)   # => '/accounts/1/landing'

Setting :use_route to nil, is equivalent to the earlier #url_for example.

Format not coming out properly?

Date, Time and DateTime may have different formats defined.

If you do:

@user.created_at.to_formatted_s(:long_ordinal)

You will get (or something):

April 16th, 2009 22:03 

But if you do:

@user.created_at.to_date.to_formatted_s(:long_ordinal)

You will get:

April 16th, 2009

So, be sure you know which one you are working with.

Do not forget to add indexes

Don’t forget to add indexes to HATM table:

add_index :developers_projects, [:developer_id, :project_id]

strip_tags method not functioning in controllers, models, or libs

It comes up with an error about white_list_sanitizer undefined in the class you’re using it in. To get around this, use:

ActionController::Base.helpers.strip_tags('string')

To shorten this, add something like this in an initializer:

class String
  def strip_tags
    ActionController::Base.helpers.strip_tags(self)
  end
end

then call it with:

'string'.strip_tags

sanitize method not functioning in controllers, models, or libs

It comes up with an error about white_list_sanitizer undefined in the class you’re using it in. To get around this, use:

ActionController::Base.helpers.sanitize('string')

To shorten this, add something like this in an initializer:

class String
  def sanitize
    ActionController::Base.helpers.sanitize(self)
  end
end

then call it with:

'string'.sanitize

Corrected link to ActiveRecord's "new_record?" method

rafaelrosafu, the correct tink to ActiveRecord’s “new_record?” method is:

"http://apidock.com/rails/ActiveRecord/Base/new_record%3F"