Question

我实现了一个类似于描述here的Yesod身份验证系统，通过查找列表中硬编码的用户名和密码可以正常工作。

我现在尝试修改此行为，通过修改 lookupUser 和 validPassword 函数来查找数据库中的用户名和密码。首先，只有 lookupUser ：

lookupUser :: Text -> Maybe Owner
lookupUser username = do 
    x <- runSqlite "db.sqlite3" . asSqlBackendReader $ selectFirst [ElementOwnerId ==. username] []
    case x of
        Nothing -> Nothing
        Just (Entity k v) -> Just $ Owner username (elementOwnerPw v)

asSqlBackendReader :: ReaderT SqlBackend m a -> ReaderT SqlBackend m a
asSqlBackendReader = id

但我收到以下错误，我不明白：

    • Couldn't match type ‘Maybe’ with ‘IO’
        arising from a functional dependency between:
          constraint ‘MonadBaseControl IO Maybe’
            arising from a use of ‘runSqlite’
          instance ‘MonadBaseControl Maybe Maybe’ at <no location info>
    • In the first argument of ‘(.)’, namely ‘runSqlite "db.sqlite3"’
      In the expression: runSqlite "db.sqlite3" . asSqlBackendReader
      In a stmt of a 'do' block:
        x <- runSqlite "db.sqlite3" . asSqlBackendReader
               $ selectFirst [ElementOwnerId ==. username] []
    |
238 |     x <- runSqlite "db.sqlite3" . asSqlBackendReader $ selectFirst [ElementOwnerId ==. username] []
    |          ^^^^^^^^^^^^^^^^^^^^^^^^

runSqlite 和 selectFirst 的签名：

runSqlite :: MonadCatchIO m => SqliteReader m a -> Pool Connection -> m a

selectFirst :: (PersistEntity val, PersistEntityBackend val ~ b) => [Filter val] -> [SelectOpt val] -> b m (Maybe (Entity val))

Yesod Hardcoded Auth具有数据库访问权限

0 个答案: