eval()

pymongo/database.py

@@ -22,6 +22,7 @@ from dbref import DBRef
 from son_manipulator import ObjectIdInjector, ObjectIdShuffler
 from collection import Collection
 from errors import InvalidName, CollectionInvalid, OperationFailure
+from code import Code
 
 # sort directions
 ASCENDING = 1
@@ -345,3 +346,23 @@ class Database(object):
         if not isinstance(dbref, DBRef):
             raise TypeError("cannot dereference a %s" % type(dbref))
         return self[dbref.collection()].find_one(dbref.id())
+
+    def eval(self, code, *args):
+        """Evaluate a JavaScript expression on the Mongo server.
+
+        Useful if you need to touch a lot of data lightly; in such a scenario
+        the network transfer of the data could be a bottleneck. The `code`
+        argument must be a JavaScript function. Additional positional
+        arguments will be passed to that function when it is run on the
+        server.
+
+        Raises TypeError if `code` is not an instance of (str, unicode). Raises
+        OperationFailure if the eval fails. Returns the result of the
+        evaluation.
+        """
+        if not isinstance(code, types.StringTypes):
+            raise TypeError("code must be an instance of (str, unicode)")
+
+        command = SON([("$eval", Code(code)), ("args", args)])
+        result = self._command(command)
+        return result.get("retval", None)

test/test_database.py

@@ -247,6 +247,26 @@ class TestDatabase(unittest.TestCase):
         key = db.test.save(obj)
         self.assertEqual(obj, db.dereference(DBRef("test", key)))
 
+    def test_eval(self):
+        db = self.connection.pymongo_test
+        db.test.remove({})
+
+        self.assertRaises(TypeError, db.eval, None)
+        self.assertRaises(TypeError, db.eval, 5)
+        self.assertRaises(TypeError, db.eval, [])
+
+        self.assertEqual(3, db.eval("function (x) {return x;}", 3))
+        self.assertEqual(3, db.eval(u"function (x) {return x;}", 3))
+
+        self.assertEqual(None, db.eval("function (x) {db.test.save({y:x});}", 5))
+        self.assertEqual(db.test.find_one()["y"], 5)
+
+        self.assertEqual(5, db.eval("function (x, y) {return x + y;}", 2, 3))
+        self.assertEqual(5, db.eval("function () {return 5;}"))
+        self.assertEqual(5, db.eval("2 + 3;"))
+
+        self.assertRaises(OperationFailure, db.eval, "5 ++ 5;")
+
     # TODO some of these tests belong in the collection level testing.
     def test_save_find_one(self):
         db = Database(self.connection, "pymongo_test")