cheat sheets.

Basic Validations
http://ar.rubyonrails.com/classes/ActiveRecord/Validations/ClassMethods.html

def validate
  unless name && name =~ /^\w+$/
    errors.add(:name, "is missing or invalid")
  end
end

def validate_on_create
  if User.find_by_name(name)
    errors.add(:name, "is already being used")
  end
end


validates_acceptance_of
  Validates that the value of the attribute is the string "1" or the value of
  the :accept parameter. Useful for checkboxes.
validates_associated
validates_confirmation_of
validates_each
validates_exclusion_of
validates_format_of
validates_inclusion_of
validates_length_of
validates_numericality_of
validates_presence_of
validates_size_of
validates_uniqueness_of

DEFAULT_VALIDATION_OPTIONS = { :on => :save, :allow_nil => false, :allow_blank
=> false, :message => nil
ALL_RANGE_OPTIONS = [ :is, :within, :in, :minimum, :maximum ].freeze
ALL_NUMERICALITY_CHECK = { :greater_than => '>', :greater_than_or_equal_to =>
'>=', :equal_to => '==', :less_than => '<', :less_than_or_equal_to => '<=', :odd
=> 'odd?', :even => 'even?' }.freeze


validates_length_of :first_name, :maximum=>30
validates_length_of :last_name, :maximum=>30, :message=>"less than {{count}} if
you don't mind"
validates_length_of :fax, :in => 7..32, :allow_nil => true
validates_length_of :phone, :in => 7..32, :allow_blank => true
validates_length_of :user_name, :within => 6..20, :too_long => "pick a shorter
name", :too_short => "pick a longer name"
validates_length_of :fav_bra_size, :minimum => 1, :too_short => "please enter at
least {{count}} character"
validates_length_of :smurf_leader, :is => 4, :message => "papa is spelled with
{{count}} characters... don't play me."
validates_length_of :essay, :minimum => 100, :too_short => "Your essay must be
at least {{count}} words."), :tokenizer => lambda {|str| str.scan(/\w+/) }