diff --git a/bson-generic.cabal b/bson-generic.cabal
--- a/bson-generic.cabal
+++ b/bson-generic.cabal
@@ -1,5 +1,5 @@
 Name:                bson-generic
-Version:             0.0.5.1
+Version:             0.0.6
 Synopsis:            Generic functionality for BSON
 Description:         This package offers easy conversion from and to BSON data type for most of user defined data types.
 License:             BSD3
diff --git a/src/Data/Bson/Generic.hs b/src/Data/Bson/Generic.hs
--- a/src/Data/Bson/Generic.hs
+++ b/src/Data/Bson/Generic.hs
@@ -91,6 +91,8 @@
 ( ToBSON(..)
 , FromBSON(..)
 , ObjectKey(..)
+, genericToBSON
+, genericFromBSON
 , keyLabel
 , constructorLabel
 ) where
@@ -108,26 +110,6 @@
 constructorLabel :: Label
 constructorLabel = u "_co"
 
-class GConstructorCount f where
-    gconstructorCount :: f a -> Int
-
-instance GConstructorCount V1 where
-    gconstructorCount _ = 0
-
-instance (GConstructorCount a) => GConstructorCount (D1 d a) where
-    gconstructorCount (M1 x) = gconstructorCount x
-
-instance (Constructor c) => GConstructorCount (C1 c a) where
-    gconstructorCount c = 1
-
-instance (GConstructorCount a, GConstructorCount b) => GConstructorCount (a :+: b) where
-    gconstructorCount (_ :: (a :+: b) r) = gconstructorCount (undefined :: a r) +
-                                           gconstructorCount (undefined :: b r)
-
-constructorCount :: (Generic a, GConstructorCount (Rep a)) => a -> Int
-constructorCount x = gconstructorCount $ from x
-
-
 ------------------------------------------------------------------------------
 
 newtype ObjectKey = ObjectKey { unObjectKey :: Maybe ObjectId } deriving (Generic, Typeable, Show, Eq)
@@ -147,92 +129,130 @@
     toBSON :: a -> Document
 
     default toBSON :: (Generic a, GConstructorCount (Rep a), GToBSON (Rep a)) => a -> Document
-    toBSON a = genericToBSON (constructorCount a) (from a)
+    toBSON val = genericToBSON (const Nothing) val
 
+class FromBSON a where
+    fromBSON :: Document -> Maybe a
+
+    default fromBSON :: (Generic a, GConstructorCount (Rep a), GFromBSON (Rep a)) => Document -> Maybe a
+    fromBSON doc = genericFromBSON (const Nothing) doc
+
+------------------------------------------------------------------------------
+
+genericToBSON :: (Generic a, GConstructorCount (Rep a), GToBSON (Rep a))
+              => (String -> Maybe String) -- ^ Function that takes a string (selector name) and returns Just transformed name or Nothing.
+              -> a                        -- ^ The value you want to conver to BSON Document.
+              -> Document                 -- ^ The resulting document.
+genericToBSON tr val = gtoBSON tr (constructorCount val) (from val)
+
+genericFromBSON :: forall a . (Generic a, GConstructorCount (Rep a), GFromBSON (Rep a))
+                => (String -> Maybe String) -- ^ Function that takes a string (selector name) and returns Just transformed name or Nothing.
+                -> Document                 -- ^ Document.
+                -> Maybe a                  -- ^ Just the value or Nothing.
+genericFromBSON tr doc = maybe Nothing (Just . to) (gfromBSON tr (constructorCount (undefined :: a)) doc)
+
+------------------------------------------------------------------------------
+
 class GToBSON f where
-    genericToBSON :: Int -> f a -> Document
+    gtoBSON :: (String -> Maybe String) -> Int -> f a -> Document
 
 -- | Unit type -> Empty document
 instance GToBSON U1 where
-    genericToBSON _ U1 = []
+    gtoBSON _ _ U1 = []
 
 -- | Sum of types
 instance (GToBSON a, GToBSON b) => GToBSON (a :*: b) where
-    genericToBSON n (x :*: y) = genericToBSON n x ++ genericToBSON n y
+    gtoBSON tr n (x :*: y) = gtoBSON tr n x ++ gtoBSON tr n y
 
 -- | Product of types
 instance (GToBSON a, GToBSON b) => GToBSON (a :+: b) where
-    genericToBSON n (L1 x) = genericToBSON n x
-    genericToBSON n (R1 x) = genericToBSON n x
+    gtoBSON tr n (L1 x) = gtoBSON tr n x
+    gtoBSON tr n (R1 x) = gtoBSON tr n x
 
 -- | Datatype information tag
 instance (GToBSON a) => GToBSON (D1 c a) where
-    genericToBSON n (M1 x) = genericToBSON n x
+    gtoBSON tr n (M1 x) = gtoBSON tr n x
 
 -- | Constructor tag
 instance (GToBSON a, Constructor c) => GToBSON (C1 c a) where
-    genericToBSON 0 (M1 x) = genericToBSON 0 x
-    genericToBSON 1 (M1 x) = genericToBSON 1 x
-    genericToBSON n c@(M1 x) = genericToBSON n x ++ [ constructorLabel =: conName c ]
+    gtoBSON tr 0 (M1 x) = gtoBSON tr 0 x
+    gtoBSON tr 1 (M1 x) = gtoBSON tr 1 x
+    gtoBSON tr n c@(M1 x) = gtoBSON tr n x ++ [ constructorLabel =: conName c ]
 
 -- | Selector tag
 instance (Val a, Selector s) => GToBSON (S1 s (K1 i a)) where
-    genericToBSON _ s@(M1 (K1 x)) = [u (selName s) =: x]
+    gtoBSON tr _ s@(M1 (K1 x)) = [sname =: x]
+        where sname = u $ maybe (selName s) id (tr $ selName s)
 
 -- | ObjectKey special treatment
 instance (Selector s) => GToBSON (S1 s (K1 i ObjectKey)) where
-    genericToBSON _ (M1 (K1 (ObjectKey (Just key)))) = [ keyLabel =: key ]
-    genericToBSON                              _ _ = []
+    gtoBSON _ _ (M1 (K1 (ObjectKey (Just key)))) = [ keyLabel =: key ]
+    gtoBSON                                _ _ _ = []
 
 -- | Constants
 instance (ToBSON a) => GToBSON (K1 i a) where
-    genericToBSON _ (K1 x) = toBSON x
+    gtoBSON _ _ (K1 x) = toBSON x
 
 ------------------------------------------------------------------------------
 
 ------------------------------------------------------------------------------
 
-class FromBSON a where
-    fromBSON :: Document -> Maybe a
-
-    default fromBSON :: (Generic a, GConstructorCount (Rep a), GFromBSON (Rep a)) => Document -> Maybe a
-    fromBSON doc = maybe Nothing (Just . to) (genericFromBSON (constructorCount (undefined :: a)) doc)
-
 class GFromBSON f where
-    genericFromBSON :: Int -> Document -> Maybe (f a)
+    gfromBSON :: (String -> Maybe String) -> Int -> Document -> Maybe (f a)
 
 instance GFromBSON U1 where
-    genericFromBSON _ doc = Just U1
+    gfromBSON _ _ doc = Just U1
 
 instance (GFromBSON a, GFromBSON b) => GFromBSON (a :*: b) where
-    genericFromBSON n doc = do
-        x <- (genericFromBSON n doc)
-        y <- (genericFromBSON n doc)
+    gfromBSON tr n doc = do
+        x <- (gfromBSON tr n doc)
+        y <- (gfromBSON tr n doc)
         return (x :*: y)
 
 instance (GFromBSON a, GFromBSON b) => GFromBSON (a :+: b) where
-    genericFromBSON n doc = left `mplus` right
-        where left  = maybe Nothing (Just . L1) (genericFromBSON n doc)
-              right = maybe Nothing (Just . R1) (genericFromBSON n doc)
+    gfromBSON tr n doc = left `mplus` right
+        where left  = maybe Nothing (Just . L1) (gfromBSON tr n doc)
+              right = maybe Nothing (Just . R1) (gfromBSON tr n doc)
 
 instance (GFromBSON a, Constructor c) => GFromBSON (C1 c a) where
-    genericFromBSON 0 doc = maybe Nothing (Just . M1) (genericFromBSON 0 doc)
-    genericFromBSON 1 doc = maybe Nothing (Just . M1) (genericFromBSON 0 doc)
-    genericFromBSON n doc = do
+    gfromBSON tr 0 doc = maybe Nothing (Just . M1) (gfromBSON tr 0 doc)
+    gfromBSON tr 1 doc = maybe Nothing (Just . M1) (gfromBSON tr 0 doc)
+    gfromBSON tr n doc = do
         cname <- BSON.lookup constructorLabel doc
         if (cname == (conName (undefined :: M1 C c a r)))
-           then maybe Nothing (Just . M1) (genericFromBSON n doc)
+           then maybe Nothing (Just . M1) (gfromBSON tr n doc)
            else Nothing
 
 instance (GFromBSON a) => GFromBSON (M1 D c a) where
-    genericFromBSON n doc = genericFromBSON n doc >>= return . M1
+    gfromBSON tr n doc = gfromBSON tr n doc >>= return . M1
 
 instance (Val a, Selector s) => GFromBSON (S1 s (K1 i a)) where
-    genericFromBSON n doc = (BSON.lookup sname doc) >>= return . M1 . K1
-        where sname = u . selName $ (undefined :: S1 s (K1 i a) r)
+    gfromBSON tr n doc = (BSON.lookup sname doc) >>= return . M1 . K1
+        where sname = u . maybe orig id $ tr orig
+              orig  = (selName $ (undefined :: S1 s (K1 i a) r))
 
 -- | ObjectKey special treatment
 instance (Selector s) => GFromBSON (S1 s (K1 i ObjectKey)) where
-    genericFromBSON n doc = Just . M1 . K1 $ ObjectKey (BSON.lookup keyLabel doc)
+    gfromBSON _ n doc = Just . M1 . K1 $ ObjectKey (BSON.lookup keyLabel doc)
 
 ------------------------------------------------------------------------------
+
+-- | Class for getting the number of constructors of type.
+class GConstructorCount f where
+    gconstructorCount :: f a -> Int
+
+instance GConstructorCount V1 where
+    gconstructorCount _ = 0
+
+instance (GConstructorCount a) => GConstructorCount (D1 d a) where
+    gconstructorCount (M1 x) = gconstructorCount x
+
+instance (Constructor c) => GConstructorCount (C1 c a) where
+    gconstructorCount c = 1
+
+instance (GConstructorCount a, GConstructorCount b) => GConstructorCount (a :+: b) where
+    gconstructorCount (_ :: (a :+: b) r) = gconstructorCount (undefined :: a r) +
+                                           gconstructorCount (undefined :: b r)
+
+constructorCount :: (Generic a, GConstructorCount (Rep a)) => a -> Int
+constructorCount x = gconstructorCount $ from x