postgresql - 如何在Haskell中使用postgresql-simple插入bytea值

我有一张桌子被定义为

CREATE TABLE users (id SERIAL PRIMARY KEY, val BYTEA);

然后我想用binary序列化我的数据结构并存储在表中，然后检索并反序列化。

{-# LANGUAGE OverloadedStrings, DeriveAnyClass #-}
import Control.Monad (forM_)
import Data.Binary (encode, decode, Binary)
import Database.PostgreSQL.Simple
import GHC.Generics (Generic)

data User = { name :: Text, email :: Text } deriving (Show, Generic, Binary)
main = do
  conn <- connect --...
  let encoded = encode User {name = "me", email = "[email protected]" }
  execute conn "INSERT INTO users(val) values(?)" $ Only encoded
  rs <- query_ conn "SELECT id, val FROM users"
  forM_ rs $ \(id,val) ->
    putStrLn $ (show (id :: Int)) ++ ": " ++ show (decode val :: User)

但我得到了错误Data.Binary.Get.runGet at position 0: not enough bytes。
查询

SELECT * FROM users;

给予

 id | val
----+-----
  1 | \x

我不知道怎么把ByteStrings映射到'BYTEA's。根据docs一切都应该正常。我做错什么了？

最佳答案

换线固定

execute conn "INSERT INTO users(val) values(?)" $ Only encoded

具有

execute conn "INSERT INTO users(val) values(?)" $ Only $ Binary encoded

因为toField(ByteString)产生Escape而toField(Binary ByteString)产生EscapeByteA

关于postgresql - 如何在Haskell中使用postgresql-simple插入bytea值，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/52198898/