support for db.eval

lib/mongo/db.rb

@@ -374,6 +374,23 @@ module XGen
           raise "Error with count command: #{doc.inspect}"
         end
 
+        # Evaluate a JavaScript expression on MongoDB.
+        # +code+ should be a string or Code instance containing a JavaScript
+        # expression. Additional arguments will be passed to that expression
+        # when it is run on the server.
+        def eval(code, *args)
+          if not code.is_a? Code
+            code = Code.new(code)
+          end
+
+          oh = OrderedHash.new
+          oh[:$eval] = code
+          oh[:args] = args
+          doc = db_command(oh)
+          return doc['retval'] if ok?(doc)
+          raise "Error with eval command: #{doc.inspect}"
+        end
+
         # Drop index +name+ from +collection_name+. Normally called from
         # Collection#drop_index or Collection#drop_indexes.
         def drop_index(collection_name, name)

tests/test_db_api.rb

@@ -451,6 +451,26 @@ class DBAPITest < Test::Unit::TestCase
     assert_equal 2, @@coll.count('$where' => Code.new('this.a > i', {'i' => 1}))
   end
 
+  def test_eval
+    assert_equal 3, @@db.eval('function (x) {return x;}', 3)
+
+    assert_equal nil, @@db.eval("function (x) {db.test_eval.save({y:x});}", 5)
+    assert_equal 5, @@db.collection('test_eval').find_first['y']
+
+    assert_equal 5, @@db.eval("function (x, y) {return x + y;}", 2, 3)
+    assert_equal 5, @@db.eval("function () {return 5;}")
+    assert_equal 5, @@db.eval("2 + 3;")
+
+    assert_equal 5, @@db.eval(Code.new("2 + 3;"))
+    assert_equal nil, @@db.eval(Code.new("return i;"))
+    assert_equal 2, @@db.eval(Code.new("return i;", {"i" => 2}))
+    assert_equal 5, @@db.eval(Code.new("i + 3;", {"i" => 2}))
+
+    assert_raise RuntimeError do
+      @@db.eval("5 ++ 5;")
+    end
+  end
+
   def test_hint
     name = @@coll.create_index('a')
     begin