respond_to_check.rb

module AttributesSort
  def self.included(receiver)
    receiver.instance_eval do
      def build_attributes(attributes)
        "[" << attributes.map!{|attribute| "object.#{attribute}"}.join(",") << "]"
      end

      def do_attributes_sort(collection, attributes)
        attribute_array_string = build_attributes(attributes)
        collection.sort_by{|object| eval(attribute_array_string)}
      end
    end
    Array.class_eval do
      def sortable_attributes?
        self.all? {|object| @attributes.all?{|attribute| object.respond_to?(attribute)}}
      end

      def class_type
        klass = self.first.class
        is_same = self.all?{|object| object.class == klass}
        raise "All objects must be of the same class type" unless is_same
        raise "All objects must respond to sort criteria"unless sortable_attributes?
        klass
      end

      def attr_sort(options = {})
        @attributes = options[:sort_by]
        raise "You must pass in sort_by criteria" unless @attributes
        class_type.do_attributes_sort(self, @attributes)
      end
    end
  end
end

# tests that reflect changes ###################################################################

require File.expand_path(File.dirname(__FILE__) + '/spec_helper')

class Person
  include AttributesSort

  attr_accessor :firstname,:lastname,:age

  def initialize(firstname="",lastname="",age=0)
    @firstname = firstname
    @lastname = lastname
    @age = age
  end
end


describe "AttributesSort" do
  before(:each) do
    @p1 = Person.new("joe","blow",89)
    @p2 = Person.new("joe","blow",12)
    @p3 = Person.new("mary","watson",32)
    @p4 = Person.new("annie","watson",9)
    @p5 = Person.new("bob","builder",12)
    @people = [@p1, @p2, @p3, @p4, @p5]
  end

  def test_sort(criteria, result)
    @people.attr_sort(:sort_by => criteria).should == result
  end

  it "sort_by standard ruby" do
    @people.sort_by{|person| [person.age,person.firstname]}.should == [@p4, @p5, @p2, @p3, @p1]
  end

  it "object must have attr accessible attributes for sort_by to work" do
    p = Person.new
    p.should respond_to(:firstname)
    p.should respond_to(:lastname)
    p.should respond_to(:age)
  end

  it "build attributes string array to be eval'd at deferred time in sort_by block'" do
    criteria = [:lastname, :age, :firstname]
    Person.build_attributes(criteria).should == "[object.lastname,object.age,object.firstname]"
  end

  it "sort by last name" do
    test_sort([:lastname], [@p1, @p2, @p5, @p4, @p3])
  end

  it "sort by age" do
    test_sort([:age], [@p4, @p2, @p5, @p3, @p1])
  end

  it "sort by age then by first name" do
    test_sort([:age, :firstname], [@p4, @p5, @p2, @p3, @p1])
  end

  it "sort by age then by last name" do
    test_sort([:age, :lastname], [@p4, @p2, @p5, @p3, @p1])
  end

  it "sort by last name then by first name then by age" do
    test_sort([:lastname,:firstname,:age], [@p2, @p1, @p5, @p4, @p3])
  end

  it "raise error if criteria is not provided" do
    lambda {test_sort(nil, [@p1, @p2, @p5, @p4, @p3])}.should raise_error("You must pass in sort_by criteria")
  end

  it "raise error if criteria is not a valid attribute of class" do
    lambda {test_sort([:blah], [@p1, @p2, @p5, @p4, @p3])}.should raise_error("All objects must respond to sort criteria")
  end

  it "raise error if objects are not of same class type" do
    @people << "some other object"
    lambda {test_sort([:age],[@p1, @p2, @p5, @p4, @p3])}.should raise_error("All objects must be of the same class type")
  end

end