如何在Yesod-Persistent中使用記錄語法

Question

爲什麼以下不工作？我知道有很多事情在引擎蓋下，User類型可能並不具有email,createdAt和updatedAt字段。不使用位置參數來實例化對象的最好方法是什麼，這很容易失控？

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase| 
User 
    email String 
    createdAt UTCTime Maybe default=CURRENT_TIME 
    updatedAt UTCTime Maybe default=CURRENT_TIME 
    deriving Show 
]] 

main :: IO() 
main = runSqlite ":memory:" $ do 
    runMigration migrateAll 
    u <- insert $ User {email="saurabhnanda@gmail.com" createdAt=Nothing updatedAt=Nothing} 

編譯錯誤：

trysql.hs:38:23: 
    ‘email’ is not a (visible) field of constructor ‘User’ 

trysql.hs:38:55: 
    ‘createdAt’ is not a (visible) field of constructor ‘User’ 

trysql.hs:38:74: 
    ‘updatedAt’ is not a (visible) field of constructor ‘User’ 

Answer 1

函數名會是這樣：userEmail，userCreatedAt，userUpdatedAt。

運行cabal REPL並瀏覽項目有助於識別Yesod生成的持久類型函數。