Add support for Set to Relation#where

Previously `#where` used to treat `Set`objects as nil, but now it treats
them as an array:

  set = Set.new([1, 2])
  Author.where(:id => set)
  # => SELECT "authors".* FROM "authors" WHERE "authors"."id" IN (1, 2)

1 files changed, 11 insertions, 0 deletions

diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 0cf44388fa..c3409a1ca8 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -848,6 +848,17 @@ class RelationTest < ActiveRecord::TestCase
     }
   end
 
+  def test_find_all_using_where_with_a_set
+    david = authors(:david)
+    mary  = authors(:mary)
+    set   = Set.new([david.id, mary.id])
+
+    assert_queries(1) {
+      relation = Author.where(:id => set)
+      assert_equal [david, mary], relation
+    }
+  end
+
   def test_exists
     davids = Author.where(:name => 'David')
     assert davids.exists?