Merge pull request #3507 from jmazzi/issue-3503

Preserve SELECT columns on the COUNT for finder_sql when possible

activerecord/lib/active_record/associations/collection_association.rb

@@ -344,8 +344,12 @@ module ActiveRecord
           if options[:counter_sql]
             interpolate(options[:counter_sql])
           else
-            # replace the SELECT clause with COUNT(*), preserving any hints within /* ... */
-            interpolate(options[:finder_sql]).sub(/SELECT\b(\/\*.*?\*\/ )?(.*)\bFROM\b/im) { "SELECT #{$1}COUNT(*) FROM" }
+            # replace the SELECT clause with COUNT(SELECTS), preserving any hints within /* ... */
+            interpolate(options[:finder_sql]).sub(/SELECT\b(\/\*.*?\*\/ )?(.*)\bFROM\b/im) do
+              count_with = $2.to_s
+              count_with = '*' if count_with.blank? || count_with =~ /,/
+              "SELECT #{$1}COUNT(#{count_with}) FROM"
+            end
           end
         end
 

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -41,6 +41,21 @@ class HasManyAssociationsTestForCountWithCountSql < ActiveRecord::TestCase
   end
 end
 
+class HasManyAssociationsTestForCountDistinctWithFinderSql < ActiveRecord::TestCase
+  class Invoice < ActiveRecord::Base
+    has_many :custom_line_items, :class_name => 'LineItem', :finder_sql => "SELECT DISTINCT line_items.amount from line_items"
+  end
+
+  def test_should_count_distinct_results
+    invoice = Invoice.new
+    invoice.custom_line_items << LineItem.new(:amount => 0)
+    invoice.custom_line_items << LineItem.new(:amount => 0)
+    invoice.save!
+
+    assert_equal 1, invoice.custom_line_items.count
+  end
+end
+
 
 
 class HasManyAssociationsTest < ActiveRecord::TestCase