无法使用持久性和`catch`函数捕获Sql异常

Question

我正在尝试使用持久性运行deleteWhere查询，但是由于外键冲突，有时此删除操作失败（我不想触发级联删除，我不希望用户如果Supplier被系统中其他地方的其他实体使用，则可以删除）。从https://github.com/yesodweb/yesod-cookbook/blob/master/cookbook/Handling-Persistence-Exception.md开始，看来我可以使用catch中的Control.Monad.Catch。

import           Control.Monad.Catch
import qualified Database.Persist as P
import           Database.PostgreSQL.Simple.Errors (ConstraintViolation(..))

data DeleteSupplierResult
  = DeleteSupplierSuccess
  | DeleteSupplierForeignKeyViolation
  | DeleteSupplierUncaughtError

deleteSupplier
  :: MonadCatch m
  => MonadIO m
  => Key Supplier
  -> SqlPersistT m DeleteSupplierResult
deleteSupplier sid =
  (DeleteSupplierSuccess <$ deleteSupplierByKey sid) `catch` (return . catchFailures)
  where
    catchFailures = \case
      ForeignKeyViolation _ _ ->
        DeleteSupplierForeignKeyViolation

      _ ->
        DeleteSupplierUncaughtError

deleteSupplierByKey :: MonadIO m => Key Supplier -> SqlPersistT m ()
deleteSupplierByKey key =
  P.deleteWhere [SupplierId P.==. key]

是我要匹配ConstraintViolation的问题，这不是引发的实际异常吗？我如何确定持久性引发的错误并将其捕获？