diff --git a/gitson.cabal b/gitson.cabal
--- a/gitson.cabal
+++ b/gitson.cabal
@@ -1,12 +1,12 @@
 name:            gitson
-version:         0.4.1
+version:         0.5.0
 synopsis:        A document store library for Git + JSON.
 description:     A simple document store library for Git + JSON, based on Aeson. Uses command line git. Transactions use flock, so it's safe even across completely separate programs!
 category:        Database, JSON, Git
 homepage:        https://github.com/myfreeweb/gitson
 author:          Greg V
-copyright:       2014 Greg V <floatboth@me.com>
-maintainer:      floatboth@me.com
+copyright:       2014-2015 Greg V <greg@unrelenting.technology>
+maintainer:      greg@unrelenting.technology
 license:         Apache-2.0
 license-file:    COPYING
 build-type:      Simple
diff --git a/library/Gitson.hs b/library/Gitson.hs
--- a/library/Gitson.hs
+++ b/library/Gitson.hs
@@ -7,6 +7,8 @@
 , transaction
 , saveDocument
 , saveNextDocument
+, saveDocumentById
+, saveDocumentByName
 , listCollections
 , listDocumentKeys
 , listEntries
@@ -39,6 +41,19 @@
 type FileName = String
 type Finder = ([(IdAndName, FileName)] -> Maybe (IdAndName, FileName))
 
+splitFindDocument :: (MonadIO i) => FilePath -> Finder -> i (Maybe (IdAndName, FileName))
+splitFindDocument collection finder = listDocumentKeys collection >>=
+  return . finder . catMaybes . map (\x -> intoFunctor (maybeReadIntString x) x)
+
+documentFullKey :: (MonadIO i) => FilePath -> Finder -> i (Maybe FileName)
+documentFullKey collection finder = splitFindDocument collection finder >>= return . (snd <$>)
+
+findById :: Int -> Finder
+findById i = find $ (== i) . fst . fst
+
+findByName :: String -> Finder
+findByName n = find $ (isSuffixOf n) . snd . fst
+
 -- | Creates a git repository under a given path.
 createRepo :: FilePath -> IO ()
 createRepo path = do
@@ -81,6 +96,24 @@
         return . nextKeyId >>=
         \nextId -> writeDocument collection (combineKey (nextId, key)) content]
 
+-- | Adds a write action to a transaction.
+-- Will update the document with the given numeric id.
+saveDocumentById :: (MonadIO i, ToJSON a) => FilePath -> Int -> a -> TransactionWriter i ()
+saveDocumentById collection i content = do
+  tell [documentFullKey collection (findById i) >>=
+        \k -> case k of
+          Just key -> writeDocument collection key content
+          Nothing -> return ()]
+
+-- | Adds a write action to a transaction.
+-- Will update the document with the given numeric id.
+saveDocumentByName :: (MonadIO i, ToJSON a) => FilePath -> String -> a -> TransactionWriter i ()
+saveDocumentByName collection n content = do
+  tell [documentFullKey collection (findByName n) >>=
+        \k -> case k of
+          Just key -> writeDocument collection key content
+          Nothing -> return ()]
+
 -- | Lists collections in the current repository.
 listCollections :: (MonadIO i) => i [FilePath]
 listCollections = liftIO $ do
@@ -111,28 +144,16 @@
   Just key -> readDocument collection key
   Nothing -> return Nothing
 
-splitFindDocument :: (MonadIO i) => FilePath -> Finder -> i (Maybe (IdAndName, FileName))
-splitFindDocument collection finder = listDocumentKeys collection >>=
-  return . finder . catMaybes . map (\x -> intoFunctor (maybeReadIntString x) x)
-
-findById :: Int -> Finder
-findById i = find $ (== i) . fst . fst
-
-findByName :: String -> Finder
-findByName n = find $ (isSuffixOf n) . snd . fst
-
 -- | Reads a document from a collection by numeric id (for example, key "00001-hello" has id 1).
 readDocumentById :: (MonadIO i, FromJSON a) => FilePath -> Int -> i (Maybe a)
 readDocumentById collection i =
-  splitFindDocument collection (findById i) >>=
-  return . (snd <$>) >>=
+  documentFullKey collection (findById i) >>=
   readDocument' collection
 
 -- | Reads a document from a collection by name (for example, key "00001-hello" has name "hello").
 readDocumentByName :: (MonadIO i, FromJSON a) => FilePath -> String -> i (Maybe a)
 readDocumentByName collection n =
-  splitFindDocument collection (findByName n) >>=
-  return . (snd <$>) >>=
+  documentFullKey collection (findByName n) >>=
   readDocument' collection
 
 -- | Returns a document's id by name (for example, "hello" will return 23 when key "00023-hello" exists).
diff --git a/test-suite/GitsonSpec.hs b/test-suite/GitsonSpec.hs
--- a/test-suite/GitsonSpec.hs
+++ b/test-suite/GitsonSpec.hs
@@ -44,6 +44,26 @@
           second <- readFile "things/000002-world.json"
           second `shouldBe` "{\n  \"val\": 2\n}"
 
+    describe "saveDocumentById" $ do
+      it "updates an entry by specified id" $ do
+        createDirectoryIfMissing True "tmp/repo/things"
+        _ <- liftIO $ writeFile "tmp/repo/things/000004-second-thing.json" "{\"val\":1}"
+        transaction "tmp/repo" $ do
+          saveDocumentById "things" 4 Thing {val = 2}
+        insideDirectory "tmp/repo" $ do
+          second <- readFile "things/000004-second-thing.json"
+          second `shouldBe` "{\n  \"val\": 2\n}"
+
+    describe "saveDocumentByName" $ do
+      it "updates an entry by specified name" $ do
+        createDirectoryIfMissing True "tmp/repo/things"
+        _ <- liftIO $ writeFile "tmp/repo/things/000004-second-thing.json" "{\"val\":1}"
+        transaction "tmp/repo" $ do
+          saveDocumentByName "things" "second-thing" Thing {val = 2}
+        insideDirectory "tmp/repo" $ do
+          second <- readFile "things/000004-second-thing.json"
+          second `shouldBe` "{\n  \"val\": 2\n}"
+
   describe "readDocument" $ do
     it "returns Just the document when reading an document by key" $ do
       createDirectoryIfMissing True "tmp/repo/things"