Merge pull request rails#9078 from senny/6865_ar_count_with_uniq

`#count` in conjunction with `#uniq` performs distinct count.
Conflicts:
	activerecord/CHANGELOG.md

activerecord/CHANGELOG.md

@@ -1,5 +1,14 @@
 ## Rails 3.2.12 (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*
+
 *   Fix `ActiveRecord::Relation#pluck` when columns or tables are reserved words.
     Backport #7536.
     Fix #8968.

activerecord/lib/active_record/relation/calculations.rb

@@ -195,7 +195,8 @@ def pluck(column_name)
     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)

activerecord/test/cases/calculations_test.rb

@@ -369,6 +369,10 @@ def test_count_with_column_parameter
     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.count(:firm_id, :conditions => "credit_limit = 50 AND firm_id IS NOT NULL")
   end