Merge pull request #9078 from senny/6865_ar_count_with_uniq

`#count` in conjunction with `#uniq` performs distinct count.

3 files changed, 15 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 278baee68f..6f3bd50f9a 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,14 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   When `#count` is used in conjunction with `#uniq` we perform `count(:distinct => true)`.
+    Fix #6865.
+
+    Example:
+
+      relation.uniq.count # => SELECT COUNT(DISTINCT *)
+
+    *Yves Senn + Kaspar Schiess*
+
 *   PostgreSQL ranges type support. Includes: int4range, int8range,
     numrange, tsrange, tstzrange, daterange
 
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index 3f154bd1cc..f10c290755 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -192,7 +192,8 @@ module ActiveRecord
     def perform_calculation(operation, column_name, options = {})
       operation = operation.to_s.downcase
 
-      distinct = options[:distinct]
+      # If #count is used in conjuction with #uniq it is considered distinct. (eg. relation.uniq.count)
+      distinct = options[:distinct] || self.uniq_value
 
       if operation == "count"
         column_name ||= (select_for_count || :all)
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index b7622705bf..be49e948fc 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -341,6 +341,10 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal 5, Account.count(:firm_id)
   end
 
+  def test_count_with_uniq
+    assert_equal 4, Account.select(:credit_limit).uniq.count
+  end
+
   def test_count_with_column_and_options_parameter
     assert_equal 2, Account.where("credit_limit = 50 AND firm_id IS NOT NULL").count(:firm_id)
   end