Use hasql-transaction

Also use hspec before-wrapper

src/PostgREST/QueryBuilder.hs

@@ -18,7 +18,6 @@ module PostgREST.QueryBuilder (
   , callProc
   , createReadStatement
   , createWriteStatement
-  , inTransaction
   , operators
   , pgFmtIdent
   , pgFmtLit
@@ -27,11 +26,9 @@ module PostgREST.QueryBuilder (
   , sourceCTEName
   , unquoted
   , ResultsWithCount
-  , Isolation(..)
   ) where
 
 import qualified Hasql.Query             as H
-import qualified Hasql.Session           as H
 import qualified Hasql.Encoders          as HE
 import qualified Hasql.Decoders          as HD
 
@@ -504,20 +501,3 @@ pgFmtAsJsonPath (Just xx) = " AS " <> last xx
 
 trimNullChars :: Text -> Text
 trimNullChars = T.takeWhile (/= '\x0')
-
-data Isolation = ReadCommitted | RepeatableRead | Serializable
-
-{- |
-  Wrap a session in a transaction of desired isolation level
--}
-inTransaction :: Isolation -> H.Session a -> H.Session a
-inTransaction lvl f = do
-  H.sql $ "begin " <> isolate <> ";"
-  r <- f
-  H.sql "commit;"
-  return r
- where
-  isolate = case lvl of
-    ReadCommitted  -> "ISOLATION LEVEL READ COMMITTED"
-    RepeatableRead -> "ISOLATION LEVEL REPEATABLE READ"
-    Serializable   -> "ISOLATION LEVEL SERIALIZABLE"