Yesod Hamlet getHomeR 找不到参考

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}
        |]

我收到这个错误

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

虽然我在模型中定义了：

Vocabulary json
    word Text
    date UTCTime
    deriving Show

PS: 我是基于yesod脚手架示例开发的：yesod-postgres

Answer 1

应该是 vocabularyDate 而不是 date。根据 yesod book 上的持久部分，

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

将生成类似于

的代码

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。

Yesod Hamlet getHomeR 找不到参考

Yesod Hamlet getHomeR can't find reference

haskell

yesod