Rails view helper for extracting value by path string

application_helper.rb

# -*- encoding : utf-8 -*-
module ApplicationHelper
  def read_value_from(object, path_string, alt_value=nil)
    return alt_value unless object && path_string
    value = object
    path_string.split(".").each do |path_component|
      return alt_value unless value.respond_to?(path_component.to_sym)
      value = value.send(path_component.to_sym)
    end
    value
  end
end

application_helper_spec.rb

# -*- encoding : utf-8 -*-
require 'spec_helper'

class ChainTestTargetNode
  def value
    "test_value_from_target"
  end
  def nil_value
    nil
  end
end
class ChainTestMidNode
  def chain_up
    ChainTestTargetNode.new
  end
end
class ChainTestSourceNode
  def chain_up
    ChainTestMidNode.new
  end
  def value
    "test_value_from_self"
  end
end


describe ApplicationHelper do

  context "read_value_from method" do
    let(:alt_value){'alt value text'}
    let(:test_object){ ChainTestSourceNode.new }

    it "should return alt value if object or path or both are nil" do
      helper.read_value_from(nil, nil, alt_value).should == alt_value
      helper.read_value_from(nil, 'test.test.test', alt_value).should == alt_value
      helper.read_value_from({}, nil, alt_value).should == alt_value
    end

    it "should return nil for alt value if isn't specified" do
      helper.read_value_from(nil, nil).should be_nil
    end

    it "should return alt value unless object respond to given path" do
      helper.read_value_from(test_object, "chain_up.chain_up.aaaa", alt_value).should == alt_value
      helper.read_value_from(test_object, "chain_up.bbbb.aaaa", alt_value).should == alt_value
      helper.read_value_from(test_object, "cccc.bbbb.aaaa", alt_value).should == alt_value
    end

    it "should return value if object respond to given path" do
      helper.read_value_from(test_object, "chain_up.chain_up.value").should == "test_value_from_target"
      helper.read_value_from(test_object, "value").should == "test_value_from_self"
    end

    it "it should return nil if object respond to given path and return nil" do
      helper.read_value_from(test_object, "chain_up.chain_up.nil_value", alt_value).should be_nil
    end
  end
end