如何在Haskell中使用postgresql-simple插入byte值

Question

我有一个表，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 = "me@home.net" }
  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)

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

查询

SELECT * FROM users;

给出

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

我想不出如何将ByteString%s映射到“be”。根据docs的说法，一切都应该正常。我哪里做错了？

Answer 1

已通过替换行修复

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

使用

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

这是因为toField(ByteString)生成Escape，而toField(Binary ByteString)生成EscapeByteA