mysql - Yesod、Persistent 和 MySQL 没有实例错误

Question

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"

模型.hs:

{-# 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")

楷模:

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)

提前致谢 :)

编辑:根据要求定义语言数据类型的 Language.hs 文件:

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)

Answer 1

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)

=> 使用模板 haskell 为其派生持久相关实例:

derivePersistField "Language"

您必须对用于模型的所有总和类型执行此操作。