`#pluck` can be used on a relation with `select` clause.

Closes #7551

3 files changed, 18 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index e9adbf0f5d..580a580ba5 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,14 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*  `#pluck` can be used on a relation with `select` clause
+   Fix #7551
+
+   Example:
+
+        Topic.select([:approved, :id]).order(:id).pluck(:id)
+
+   *Yves Senn*
+
 *   Do not create useless database transaction when building `has_one` association.
 
     Example:
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index a7d2f4bd24..df27318678 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -165,7 +165,9 @@ module ActiveRecord
       if has_include?(column_names.first)
         construct_relation_for_association_calculations.pluck(*column_names)
       else
-        result  = klass.connection.select_all(select(column_names).arel, nil, bind_values)
+        relation = spawn
+        relation.select_values = column_names
+        result = klass.connection.select_all(relation.arel, nil, bind_values)
         columns = result.columns.map do |key|
           klass.column_types.fetch(key) {
             result.column_types.fetch(key) {
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index abbf2a765e..65d28ea028 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -580,4 +580,10 @@ class CalculationsTest < ActiveRecord::TestCase
 
     assert_equal ["Over There"], Possession.pluck(:where)
   end
+
+  def test_pluck_replaces_select_clause
+    taks_relation = Topic.select(:approved, :id).order(:id)
+    assert_equal [1,2,3,4], taks_relation.pluck(:id)
+    assert_equal [false, true, true, true], taks_relation.pluck(:approved)
+  end
 end