Hi all,
Below my .sig is a little Persist/Esqueleto program that works correctly.
The getUserCount function does thr right thing and returns the number of
rows in the User table. However, what I'd like is a generic function
that returns the row count of any table, something vaguely like this:
queryRowCount :: tableType -> SqlPersist IO Int64
queryRowCount tableName = do
[Value x] <- select . from $ \(_ :: SqlExpr (Entity tableName)) ->
return countRows
return x
Is there any way to do this? Its probably possible in Agda, but can it
be made to work with GHC?
Cheers,
Erik
--
----------------------------------------------------------------------
Erik de Castro Lopo
http://www.mega-nerd.com/
{-# LANGUAGE FlexibleContexts, GADTs, GeneralizedNewtypeDeriving, OverloadedStrings,
QuasiQuotes, ScopedTypeVariables, TypeFamilies, TemplateHaskell #-}
import Control.Monad (void)
import Control.Monad.IO.Class (liftIO)
import Database.Esqueleto
import Database.Persist.Sqlite
import Database.Persist.TH
import GHC.Int (Int64)
share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persist|
User
firstName String
lastName String
emailAddress String
UserName firstName lastName
deriving Show
Project
name String
description String
deriving Show
|]
-- This works, but only for the User table.
queryUserCount :: SqlPersist IO Int64
queryUserCount = do
[Value x] <- select . from $ \(_ :: SqlExpr (Entity User)) ->
return countRows
return x
main :: IO ()
main = withSqliteConn ":memory:" $ runSqlConn $ do
void $ runMigrationSilent migrateAll
void $ insert $ User "Fred" "Smith" "