Returns true if no errors were added otherwise false. Only executes validations that have no :groups option specified
Only executes a specified validation. The argument should follow a pattern based on the key of the validation.
Examples: * validates_presence_of :name can be run with obj.validate_only("presence_of/name") * validates_presence_of :birthday, :key => "a key" can be run with obj.validate_only("presence_of/a key")