Notes posted to Ruby on Rails

collection.exists?(conditions)

The created association method also supports the ‘exists?’ method, similar to ActiveRecord::Base#exists?

has_and_belongs_to_many :categories
...
categories.exist?(1)   # Check whether there's a relation with a Category
                       # object whose id is 1.
categories.exist?(:id => 1)    # ditto
categories.exist?(['id', 1])   # ditto
categories.exist?(:name => 'Anime')

update_on and update_at only set on attribute change

If you call save, and no attributes are “dirty” (changed), then an update query will not happen against the database, and thus updated_at and updated_on will not be set.

You’ll need to modify at least one field to get updated_at and updated_on to set themselves.

Bang methods also need will_change!

As it says here at the bottom if you do in-place modifications using << you’ll need to call the will_change method!

This also goes for bang methods. So:

person = Person.first
person.name.downcase!
person.save

will not save anything! Save will never be called. To get the name saved you need to do

person = Person.first
person.name_will_change!
person.name.downcase!
person.save

This will save the name.

Test

Test of notes…

Set cache time-to-live

You can specify time-to-live for the cached item in seconds with :expires_in option.

class ListsController < ApplicationController
  caches_action :index, :expires_in => 1.hour
end

Nil V.S. Empty String HTML Options

There is a difference between an empty string and nil value for options hash.

Code Sample

content_tag( :div, 'Hello World!', :class=>'') # => "<div class="">Hello World!</div>"
content_tag( :div, 'Hello World!', :class=>nil) # => "<div>Hello World!</div>"

Using memcached as a session store

Because of Ruby’s CGI library limitations, store cannot have any configuration options. Basically this means that you cannot easily run memcached on a different port (or with any non-default settings for that matter).

You can bypass this limitation with this ugly hack (environment.rb):

cache_params = *([memcache_servers, memcache_options].flatten)
CACHE = MemCache.new(*cache_params)
ActionController::CgiRequest::DEFAULT_SESSION_OPTIONS.merge!({ 'cache' => CACHE })

In your initializer block, just configure session_store normally:

config.session_store = :mem_cache_store

I think this should be fixed to work like cache_store= does.