Initial code pull from yesod

LICENSE

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+The following license covers this documentation, and the source code, except
+where otherwise indicated.
+
+Copyright 2010, Michael Snoyman. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice,
+  this list of conditions and the following disclaimer in the documentation
+  and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS "AS IS" AND ANY EXPRESS OR
+IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
+EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY DIRECT, INDIRECT,
+INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
+OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Yesod/Persist.hs

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+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE FlexibleContexts #-}
+module Yesod.Persist
+    ( YesodPersist (..)
+    , get404
+    , getBy404
+    , module Database.Persist
+    ) where
+
+import Database.Persist
+import Control.Monad.Trans.Class (MonadTrans (..))
+import Control.Failure (Failure)
+
+import Yesod
+
+class YesodPersist y where
+    type YesodDB y :: (* -> *) -> * -> *
+    runDB :: YesodDB y (GHandler sub y) a -> GHandler sub y a
+
+-- Get the given entity by ID, or return a 404 not found if it doesn't exist.
+get404 :: (PersistBackend (t m), PersistEntity val, Monad (t m),
+           Failure ErrorResponse m, MonadTrans t)
+       => Key val -> t m val
+get404 key = do
+    mres <- get key
+    case mres of
+        Nothing -> lift notFound
+        Just res -> return res
+
+-- Get the given entity by unique key, or return a 404 not found if it doesn't
+-- exist.
+getBy404 :: (PersistBackend (t m), PersistEntity val, Monad (t m),
+             Failure ErrorResponse m, MonadTrans t)
+         => Unique val -> t m (Key val, val)
+getBy404 key = do
+    mres <- getBy key
+    case mres of
+        Nothing -> lift notFound
+        Just res -> return res

yesod-persistent.cabal

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+name:            yesod-persistent
+version:         0.0.0
+license:         BSD3
+license-file:    LICENSE
+author:          Michael Snoyman <michael@snoyman.com>
+maintainer:      Michael Snoyman <michael@snoyman.com>
+synopsis:        Some helpers for using Persistent from Yesod.
+category:        Web, Yesod, Database
+stability:       Stable
+cabal-version:   >= 1.6
+build-type:      Simple
+homepage:        http://docs.yesodweb.com/
+
+library
+    build-depends:   base                      >= 4        && < 5
+                   , yesod                     >= 0.7      && < 0.8
+                   , persistent                >= 0.4      && < 0.5
+                   , failure                   >= 0.1      && < 0.2
+                   , transformers              >= 0.2      && < 0.3
+    exposed-modules: Yesod.Persist
+    ghc-options:     -Wall
+
+source-repository head
+  type:     git
+  location: git://github.com/snoyberg/yesod-persistent.git