Make ActiveRecord::Relation#last to reverse SQL order

instead of loading the relation into memory

1 files changed, 36 insertions, 8 deletions

diff --git a/activerecord/test/cases/finder_test.rb b/activerecord/test/cases/finder_test.rb
index 75a74c052d..0004c98c8a 100644
--- a/activerecord/test/cases/finder_test.rb
+++ b/activerecord/test/cases/finder_test.rb
@@ -516,16 +516,44 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal Topic.order("title").to_a.last(2), Topic.order("title").last(2)
   end
 
-  def test_last_with_integer_and_order_should_not_use_sql_limit
-    query = assert_sql { Topic.order("title").last(5).entries }
-    assert_equal 1, query.length
-    assert_no_match(/LIMIT/, query.first)
+  def test_last_with_integer_and_order_should_use_sql_limit
+    relation = Topic.order("title")
+    assert_queries(1) { relation.last(5) }
+    assert !relation.loaded?
   end
 
-  def test_last_with_integer_and_reorder_should_not_use_sql_limit
-    query = assert_sql { Topic.reorder("title").last(5).entries }
-    assert_equal 1, query.length
-    assert_no_match(/LIMIT/, query.first)
+  def test_last_with_integer_and_reorder_should_use_sql_limit
+    relation = Topic.reorder("title")
+    assert_queries(1) { relation.last(5) }
+    assert !relation.loaded?
+  end
+
+  def test_last_on_loaded_relation_should_not_use_sql
+    relation  = Topic.limit(10).load
+    assert_no_queries do
+      relation.last
+      relation.last(2)
+    end
+  end
+
+  def test_last_with_irreversible_order
+    assert_deprecated do
+      Topic.order("coalesce(author_name, title)").last
+    end
+  end  
+
+  def test_last_on_relation_with_limit_and_offset
+    post = posts('sti_comments')
+
+    comments = post.comments.order(id: :asc)
+    assert_equal comments.limit(2).to_a.last, comments.limit(2).last
+    assert_equal comments.limit(2).to_a.last(2), comments.limit(2).last(2)
+    assert_equal comments.limit(2).to_a.last(3), comments.limit(2).last(3)
+
+    comments = comments.offset(1)
+    assert_equal comments.limit(2).to_a.last, comments.limit(2).last
+    assert_equal comments.limit(2).to_a.last(2), comments.limit(2).last(2)
+    assert_equal comments.limit(2).to_a.last(3), comments.limit(2).last(3)
   end
 
   def test_take_and_first_and_last_with_integer_should_return_an_array