Esqueleto在实体ID上的位置

Question

我一直在遵循Yesod的SQL连接中的示例，我想在内部联接示例中添加一个where_子句--它应该只显示作者ID高于1的博客。

我认为我的错误可能是我正在做E.val 1，但不确定如何传递它它期望得到的Key

getHomeR :: Handler Html
getHomeR = do
    blogs <- runDB
           $ E.select
           $ E.from $ \(blog `E.InnerJoin` author) -> do
                E.on $ blog ^. BlogAuthor E.==. author ^. AuthorId
                E.where_ $ author ^. AuthorId E.>. (E.val 1) -- how to pass ID 1
                E.limit 5
                return
                    ( blog   ^. BlogId
                    , blog   ^. BlogTitle
                    , author ^. AuthorName
                    )

Answer 1

多亏了这个要旨，我找到了答案

以下是完整的示例：

import Database.Persist.Sql (toSqlKey)
import qualified Database.Esqueleto      as E
import           Database.Esqueleto      ((^.))

getHomeR :: Handler TypedContent
getHomeR = do
    let authorID = toSqlKey 1 :: AuthorId -- cast 1 to the expected key
    let blogsSrc =
             E.selectSource
           $ E.from $ \(blog `E.InnerJoin` author) -> do
                E.on $ blog ^. BlogAuthor E.==. author ^. AuthorId
                E.where_ $ author ^. AuthorId E.>. E.val authorID
                return
                    ( blog   ^. BlogId
                    , blog   ^. BlogTitle
                    , author ^. AuthorName
                    )