1 files changed, 27 insertions, 0 deletions
diff --git a/lib/arel/engines/memory/primitives.rb b/lib/arel/engines/memory/primitives.rb
new file mode 100644
index 0000000000..935b34f5ee
--- /dev/null
+++ b/lib/arel/engines/memory/primitives.rb
@@ -0,0 +1,27 @@
+module Arel
+  class Attribute
+    def eval(row)
+      row[self]
+    end
+  end
+
+  class Value
+    def eval(row)
+      value
+    end
+  end
+
+  class Ordering
+    def eval(row1, row2)
+      (attribute.eval(row1) <=> attribute.eval(row2)) * direction
+    end
+  end
+
+  class Descending < Ordering
+    def direction; -1 end
+  end
+
+  class Ascending < Ordering
+    def direction; 1 end
+  end
+end