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我已经制作了这段代码，但我对两件事感到困惑：

  • 为什么这两个部分的工作方式不同，一个记录而另一个没有？
  • 如果添加了 NoLoggingT 包装器，为什么第二部分会记录selectFoobars？

代码：

{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE OverloadedStrings #-}

module Main where

import Control.Monad.IO.Class
import Control.Monad.Logger.CallStack
import Control.Monad.Trans.Reader (ReaderT)
import Control.Monad.Trans.Resource (ResourceT)
import Data.String.Class (toString)
import Database.Esqueleto
import Database.Persist.Sqlite (createSqlitePool)
import qualified Database.Persist.Sqlite as P
import Database.Persist.TH
import GHC.Natural
import System.Log.FastLogger (fromLogStr)

instance MonadLogger IO where
  monadLoggerLog _loc _src _lvl msg =
    putStrLn (toString (fromLogStr (toLogStr msg)))

share
  [mkPersist sqlSettings, mkMigrate "migrateAll"]
  [persistLowerCase|
Foo
  bar Natural
|]

runSomeQuery :: ConnectionPool -> Natural -> IO (Maybe Natural)
runSomeQuery pool aid = do
  flip runSqlPersistMPool pool $ do
    runMigration migrateAll
    _ <- selectFooBars aid
    return Nothing

selectFooBars ::
     Natural -> ReaderT SqlBackend (NoLoggingT (ResourceT IO)) [Entity Foo]
selectFooBars aid = do
  logDebugN "This should not log?"
  select . from $ \s -> do
    where_ $ (s ^. FooBar ==. val aid)
    limit 1
    return s

main :: IO ()
main = do
  logDebugN "MAIN"
  P.runSqlite ":memory:" $ do
    logDebugN "STARTING UP 01"
    runMigration migrateAll
    _ <- selectFooBars 123
    return ()
  budgetPool <- createSqlitePool ":memory:" 1
  logDebugN ">>>>>>>>>>>>>>>"
  logDebugN ">>>>>>>>>>>>>>>"
  logDebugN ">>>>>>>>>>>>>>>"
  logDebugN "STARTING UP 02"
  _ <- runSomeQuery budgetPool 975
  return ()

可以在https://github.com/k-bx/nologesqueleto找到完全可构建的 repo

4

1 回答 1

1

似乎日志记录功能已分配给连接信息本身，并createSqlPool分配给您运行的任何位置createSqlitePool：

createSqlPool
    :: (MonadLogger m, MonadUnliftIO m, IsSqlBackend backend)
    => (LogFunc -> IO backend)
    -> Int
    -> m (Pool backend)
createSqlPool mkConn size = do
    logFunc <- askLogFunc
    liftIO $ createPool (mkConn logFunc) close' 1 20 size

并runSqlite在 a 中显式运行其代码NoLoggingT：

runSqlite :: (MonadUnliftIO m, IsSqlBackend backend)
          => Text -- ^ connection string
          -> ReaderT backend (NoLoggingT (ResourceT m)) a -- ^ database action
          -> m a
runSqlite connstr = runResourceT
                  . runNoLoggingT
                  . withSqliteConn connstr
                  . runSqlConn

因此，如果您将代码更改为：

  budgetPool <- runNoLoggingT $ createSqlitePool ":memory:" 1

它将停止记录。它仍然不尊重类型注释NoLoggingT中的selectFooBars，这有点令人困惑。

于 2018-08-03T14:19:19.557 回答