Add Persistable instances for HDBC.

schema-th/src/Database/HDBC/Record/Persistable.hs

@@ -0,0 +1,32 @@
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+
+module Database.HDBC.Record.Persistable (
+  persistableSingleton
+  ) where
+
+import Database.Record.Persistable
+  (Singleton, singleton, runSingleton,
+   persistableNullValue, PersistableNull (..),
+   PersistableValue, persistableValue,
+   PersistableRecord, persistableRecordFromValue,
+   Persistable (persistable))
+
+import Data.Convertible (Convertible)
+import Database.HDBC (SqlValue(SqlNull), fromSql, toSql)
+
+persistableSqlValue :: (Convertible SqlValue a, Convertible a SqlValue)
+                       => PersistableValue SqlValue (Singleton a)
+persistableSqlValue =  persistableValue (singleton . fromSql) (toSql . runSingleton)
+
+persistableSingleton :: (Convertible SqlValue a, Convertible a SqlValue)
+                     => PersistableRecord SqlValue (Singleton a)
+persistableSingleton =  persistableRecordFromValue persistableSqlValue
+
+instance PersistableNull SqlValue  where
+  persistableNull = persistableNullValue SqlNull
+
+instance (Convertible SqlValue a, Convertible a SqlValue)
+         => Persistable SqlValue (Singleton a)  where
+  persistable = persistableSingleton