Yesod Hamlet getHomeR找不到参考资料

Question

getHomeR :: Handler Html
getHomeR = do
    wordList <- runDB $ selectList [] [] :: HandlerT App IO [Entity Vocabulary]
    defaultLayout
        [whamlet|
            <ul>
                $forall Entity wordid wordItem <- wordList
                    <li>
                        <a href=@{HomeR}>#{date wordItem}
        |]

我得到了这个错误

Variable not in scope: date :: Vocabulary -> a0

虽然我已经在模型中定义了：

Vocabulary json
    word Text
    date UTCTime
    deriving Show

PS:我正在基于yesod scaffold示例进行开发: yesod-postgres

Answer 1

它应该是vocabularyDate而不只是date。根据yesod book上的持久化部分，

mkPersist sqlSettings [persistLowerCase|
Person
    name String
    age Int
    deriving Show
|]

将生成如下代码

data Person = Person
    { personName :: !String
    , personAge :: !Int
    }
  deriving Show
 ...

如您所见，字段名称以数据名称为前缀(personName而不是name)。这是Haskell中避免名称冲突的标准做法。