Update example.

relational-join-HDBC-pgTest/sample/1/querySample.hs

@@ -17,8 +17,9 @@ import Database.HDBC.Record.Query (runQuery)
 import Database.HDBC.Session (withConnectionIO)
 
 
-groupMemberShip :: QueryJoin (Projection (Maybe Membership, Group))
+groupMemberShip :: Relation (Maybe Membership, Group)
 groupMemberShip =
+  relation $
   [ m >*< g
   | m  <- queryMaybe membership
   , g  <- query      group
@@ -30,30 +31,30 @@ userGroup0 =
   relation $
   [ u   >*< mg !? snd'
   | u   <- queryMaybe user
-  , mg  <- queryMaybe $ relation groupMemberShip
+  , mg  <- queryMaybe $ nested groupMemberShip
           -- Call one subquery via relation layer
           -- Simple implementation.
-          -- Complex SQL. Nested table form joins.
+          -- Nested SQL. Nested table form joins.
 
   , ()  <- on $ u !? User.id' .=. flatten (mg !? fst') !? userId'
 
   , ()  <- asc $ u !? User.id'
   ]
 
--- userGroup1 :: Relation (Maybe User, Maybe Group)
--- userGroup1 =
---   relation $
---   [ u >*< mg !? snd'
---   | u  <- queryMaybe user
---   , mg <- queryMergeMaybe groupMemberShip
---           -- Directly merge another QueryJoin monad.
---           -- Complex implementation.
---           -- Simple SQL. Flat table form joins.
+userGroup1 :: Relation (Maybe User, Maybe Group)
+userGroup1 =
+  relation $
+  [ u >*< mg !? snd'
+  | u  <- queryMaybe user
+  , mg <- queryMaybe groupMemberShip
+          -- Directly merge another QueryJoin monad.
+          -- Complex implementation.
+          -- Flat SQL. Flat table form joins.
 
---   , () <- on $ u !? User.id' .=. flatten (mg !? fst') !? userId'
+  , () <- on $ u !? User.id' .=. flatten (mg !? fst') !? userId'
 
---   , ()  <- asc $ u !? User.id'
---   ]
+  , ()  <- asc $ u !? User.id'
+  ]
 
 runAndPrint :: (Show a, IConnection conn, FromSql SqlValue a) => conn -> Relation a -> IO ()
 runAndPrint conn rel = do
@@ -66,7 +67,7 @@ run :: IO ()
 run =  withConnectionIO connect
        (\conn -> do
            runAndPrint conn userGroup0
---           runAndPrint conn userGroup1
+           runAndPrint conn userGroup1
        )
 
 main :: IO ()