mysql之Yesod、Persistent 和 MySQL 没有实例错误

我不确定这篇文章要包含什么，因为我真的不明白错误消息，所以我只包含了错误、Model.hs 文件和模型。我正在为 MySQL 使用 Yesod 脚手架站点。我使用的操作系统是 Ubuntu。如果您需要查看任何其他代码，例如数据定义然后只是询问。

错误信息:

[ 6 of 20] Compiling Model            ( src/Model.hs, .stack-work/dist/x86_64-linux/Cabal-1.24.2.0/build/Model.o ) 
 
/home/james/ConVoke/convoke-website/src/Model.hs:24:7: error: 
    • No instance for (persistent-2.7.0:Database.Persist.Sql.Class.PersistFieldSql 
                         Language) 
        arising from a use of ‘persistent-2.7.0:Database.Persist.Sql.Class.sqlType’ 
    • In the fourth argument of ‘FieldDef’, namely 
        ‘persistent-2.7.0:Database.Persist.Sql.Class.sqlType 
           (Data.Proxy.Proxy :: Data.Proxy.Proxy Language)’ 
      In the expression: 
        FieldDef 
          (HaskellName (packPTH "language")) 
          (DBName (packPTH "language")) 
          (FTTypeCon Nothing (packPTH "Language")) 
          (persistent-2.7.0:Database.Persist.Sql.Class.sqlType 
             (Data.Proxy.Proxy :: Data.Proxy.Proxy Language)) 
          [] 
          True 
          NoReference 
      In the ‘entityFields’ field of a record 
 
--  While building package website-0.0.0 using: 
      /home/james/.stack/setup-exe-cache/x86_64-linux/Cabal-simple_mPHDZzAJ_1.24.2.0_ghc-8.0.2 --builddir=.stack-work/dist/x86_64-linux/Cabal-1.24.2.0 build lib:website --ghc-options " -ddump-hi -ddump-to-file" 

{-# LANGUAGE EmptyDataDecls             #-} 
{-# LANGUAGE FlexibleInstances          #-} 
{-# LANGUAGE GADTs                      #-} 
{-# LANGUAGE GeneralizedNewtypeDeriving #-} 
{-# LANGUAGE MultiParamTypeClasses      #-} 
{-# LANGUAGE NoImplicitPrelude          #-} 
{-# LANGUAGE OverloadedStrings          #-} 
{-# LANGUAGE TemplateHaskell            #-} 
{-# LANGUAGE TypeFamilies               #-} 
module Model where 
 
import ClassyPrelude.Yesod 
import Database.Persist.Quasi 
 
import Import.Game 
import Import.Language 
import Import.Profile 
 
-- You can define all of your database entities in the entities file. 
-- You can find more information on persistent and how to declare entities 
-- at: 
-- http://www.yesodweb.com/book/persistent/ 
share [mkPersist sqlSettings, mkMigrate "migrateAll"] 
    $(persistFileWith lowerCaseSettings "config/models") 

Player 
     name Text 
     username Text 
     dob Day 
     language Language 
     tournaments [TournamentResult] 
     deriving (Show) 
 
 PlatformAccount 
     player PlayerId 
     platform Platform 
     account Text 
     deriving (Show) 
 
 SocialAccount 
     player PlayerId 
     site SocialSite 
     account Text 
     deriving (Show) 
 
 PastTeam 
     player PlayerId 
     team TeamId 
     yearJoined Int 
     yearLeft Int 
     deriving (Show) 
 
 TournamentResult 
     player PlayerId 
     team TeamId 
     name Text 
     placing Text 
     year Int 
     deriving (Show) 
 
 Roster 
     name Text 
     game Game 
     team TeamId 
     players [PlayerId] 
     creationDay Day 
     deriving (Show) 
 
 PlayerRole 
     roster RosterId 
     player PlayerId 
     role Role 
     deriving (Show) 
 
 CompetitiveGame 
     game Game 
     platform Platform 
     role Role 
     availability Availability 
     playingSince Int 
     deriving (Show) 
 
 Team 
     name Text 
     creationDay Day 
     deriving (Show) 

module Import.Language where 
 
allLanguages :: [Language] 
allLanguages = [Afrikanns ..] 
 
data Language = Afrikanns | 
                Albanian | 
                Arabic | 
                Armenian | 
                Basque | 
                Bengali | 
                Bulgarian | 
                Catalan | 
                Cambodian | 
                Chinese_Mandarin | 
                Croation | 
                Czech | 
                Danish | 
                Dutch | 
                English | 
                Estonian | 
                Fiji | 
                Finnish | 
                French | 
                Georgian | 
                German | 
                Greek | 
                Gujarati | 
                Hebrew | 
                Hindi | 
                Hungarian | 
                Icelandic | 
                Indonesian | 
                Irish | 
                Italian | 
                Japanese | 
                Javanese | 
                Korean | 
                Latin | 
                Latvian | 
                Lithuanian | 
                Macedonian | 
                Malay | 
                Malayalam | 
                Maltese | 
                Maori | 
                Marathi | 
                Mongolian | 
                Nepali | 
                Norwegian | 
                Persian | 
                Polish | 
                Portuguese | 
                Punjabi | 
                Quechua | 
                Romanian | 
                Russian | 
                Samoan | 
                Serbian | 
                Slovak | 
                Slovenian | 
                Spanish | 
                Swahili | 
                Swedish  | 
                Tamil | 
                Tatar | 
                Telugu | 
                Thai | 
                Tibetan | 
                Tonga | 
                Turkish | 
                Ukranian | 
                Urdu | 
                Uzbek | 
                Vietnamese | 
                Welsh | 
                Xhosa 
                deriving (Enum, Show, Eq) 

请您参考如下方法:

该错误表明它无法找到与总和类型相关的 Persistent 实例。你必须做两件事来修复它:

=> 确保导出 Show和 Read求和类型的实例。例子:

data Language = JS | Haskell deriving (Eq, Show, Read, Ord) 

derivePersistField "Language"