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 valid")
  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