queueAvailableIds function

src/Database/PGMQ/Simple.hs

@@ -33,7 +33,8 @@ module Database.PGMQ.Simple
   , sendMessage
   , sendMessages
   , setMessageVt
-  , queueAvailableLength )
+  , queueAvailableLength
+  , queueAvailableIds )
 where
 
 
@@ -279,6 +280,14 @@ queueAvailableLength conn queue = do
   [PSQL.Only len] <- PSQL.query conn [sql| SELECT COUNT(*) FROM ? WHERE vt <= now() |] (PSQL.Only tableId) :: IO [PSQL.Only Int]
   return len
 
+-- | Same as 'queryAvailableLength' but returns the ids of messages.
+queueAvailableIds :: PSQL.Connection -> Queue -> IO [MessageId]
+queueAvailableIds conn queue = do
+  let queueTable = "q_" <> queue
+  let tableId = PSQL.QualifiedIdentifier (Just "pgmq") $ T.pack queueTable
+  ret <- PSQL.query conn [sql| SELECT msg_id FROM ? WHERE vt <= now() |] (PSQL.Only tableId) :: IO [PSQL.Only MessageId]
+  return $ (\(PSQL.Only msgId) -> msgId) <$> ret
+
 
 {-|
  A utility function: sometimes pgmq throws an error that a table (for