Fix .select to always include required part

For instance if `channel = Yt::Channel.new(id: ..).select(:snippet)`
and then I ask for `channel.view_count`, the `:statistics` part should
be added to the request even if it was not specified at the beginning.

CHANGELOG.md

@@ -6,6 +6,10 @@ For more information about changelogs, check
 [Keep a Changelog](http://keepachangelog.com) and
 [Vandamme](http://tech-angels.github.io/vandamme).
 
+## 0.1.2 - 2017-04-06
+
+* [BUGFIX] Fix cases like `channel.select(:snippet).view_count` where attribute does not belong to any selected part.
+
 ## 0.1.1 - 2017-04-04
 
 * [ENHANCEMENT] Add :defaults to `has_attribute`

lib/yt/core/version.rb

@@ -3,6 +3,6 @@ module Yt
   module Core
     # @return [String] the SemVer-compatible gem version.
     # @see http://semver.org
-    VERSION = '0.1.1'
+    VERSION = '0.1.2'
   end
 end

lib/yt/resource.rb

@@ -6,7 +6,7 @@ class Resource
     # @option data [String] :id The unique ID of a YouTube resource.
     def initialize(data = {})
       @data = data
-      @selected_data_parts = nil
+      @selected_data_parts = []
     end
 
     # @return [String] the resource’s unique ID.
@@ -65,7 +65,7 @@ def fetch_part(required_part)
         fetch resources_path, resource_params(options)
       end
 
-      parts = @selected_data_parts || [required_part]
+      parts = (@selected_data_parts + [required_part]).uniq
       if (resource = resources.select(*parts).first)
         parts.each{|part| @data[part] = resource.data[part]}
         @data[required_part]