如何按列值选择记录？

Question

我的配置/模型中有一个非常简单的数据

Author
  name Text

我希望按名称选择作者而不是ID 我试过这个（信息来自表格）：

FormSuccess book -> do
    result <- runDB $ selectSource [ AuthorName ==. title book]

书是一个数据

data FormBook = FormBook {
  isbn :: Text
  , author :: Text
  , title :: Text
  , description :: Maybe Text
}

但是我收到了这个错误

Couldn't match type `[SelectOpt Author]' with `HandlerT App IO'
Expected type: YesodPersistBackend
             App
             (HandlerT App IO)
             (Data.Conduit.Internal.Source m0 (Entity Author))
Actual type: [SelectOpt Author]
           -> Data.Conduit.Internal.Source m0 (Entity Author)
In the return type of a call of `selectSource'
Probable cause: `selectSource' is applied to too few arguments
In the second argument of `($)', namely
`selectSource [AuthorName ==. (author book)]'
 In a stmt of a 'do' block:
authorresult <- runDB $ selectSource [AuthorName ==. (author book)]

我在Author PersistenceEntity和PersistenceField之前尝试过，但它们不在范围内。 除了原始查询之外，我没有任何其他想法。