Merge pull request #55 from github/3-0-github+pluck

Backport pluck to 3-0-github

activerecord/lib/active_record/relation/calculations.rb

@@ -156,6 +156,15 @@ module ActiveRecord
       0
     end
 
+    def pluck(column_name)
+      if column_name.is_a?(Symbol) && column_names.include?(column_name.to_s)
+        column_name = "#{connection.quote_table_name(table_name)}.#{connection.quote_column_name(column_name)}"
+      end
+
+      klass.connection.select_all(select(column_name).to_sql).map { |attributes|
+        attributes.values.first
+      }
+    end
     private
 
     def perform_calculation(operation, column_name, options = {})

activerecord/test/cases/calculations_test.rb

@@ -379,4 +379,8 @@ class CalculationsTest < ActiveRecord::TestCase
     distinct_authors_for_approved_count = Topic.group(:approved).count(:author_name, :distinct => true)[true]
     assert_equal distinct_authors_for_approved_count, 2
   end
+
+  def test_pluck
+    assert_equal [50, 50, 50, 60, 55, 53], Account.order("id ASC").pluck(:credit_limit)
+  end
 end