sqlite - Persistent 的新手问题

Question

所以我打算在 Sqlite 中使用 Persistent 0.9.0.1，我正在阅读教程:http://www.yesodweb.com/book/persistent

带有插入和查询的简单片段无法编译:

-- START
{-# LANGUAGE QuasiQuotes, TypeFamilies, GeneralizedNewtypeDeriving, TemplateHaskell,
             OverloadedStrings, GADTs, FlexibleContexts #-}
import Database.Persist
import Database.Persist.TH
import Database.Persist.Sqlite
import Control.Monad.IO.Class (liftIO)

share [mkPersist sqlSettings, mkSave "entityDefs"] [persist|
Person
    name String
    age Int
|]

main = withSqliteConn ":memory:" $ runSqlConn $ do
    runMigration $ migrate entityDefs (undefined :: Person) -- this line added: that's it!
    michaelId <- insert $ Person "Michael" 26
    michael <- get michaelId
    liftIO $ print michael
-- STOP

倾倒接头显示没有 promise Eq , Show生成的人的实例，奇怪的:

data PersonGeneric (backend :: (* -> *) -> * -> *)
    = Person {personName :: String, personAge :: Int}
type Person =
    PersonGeneric Database.Persist.GenericSql.Raw.SqlPersist

我是这样破解的:

    liftIO $ putStrLn $ "name: " ++ (personName $ fromJust michael) ++ ", age: " ++ (show $ personAge $ fromJust michael)

然后插入失败，无法从 Sqlite 取回主键:

Migrating: CREATE TABLE "person"("id" INTEGER PRIMARY KEY,"name" VARCHAR NOT NULL,"age" INTEGER NOT NULL)
proto: Pattern match failure in do expression at Database/Persist/GenericSql.hs:109:25-45

有什么想法吗？ Persistent 是否与 Sqlite 一起使用？

Answer 1

从 0.8 版到 0.9 版发生了变化，我们不再包含 Eq和 Show默认情况下的实例。要添加它们，请在 age Int 下添加以下行:

deriving Show Eq

这本书仍然针对 Yesod 0.10 版本，但我会在接下来的几天内尝试更新它。