haskell-持久性:如何在第二个表中使用外键作为主键

Question

UPDATE -找到错误的根本原因，但不知道如何解决

我刚刚发现，这种行为的根源不是使用sql=…，而是使用第一个表的主键作为外部和主键。

Post
  topic String

  deriving Show Eq

PostContent
  Id PostId
  content String

  deriving Show Eq

因此，问题仍然存在：

我可以用持久的方式表示主键是外键吗？-从的角度来看，这是有意义的(至少我认为是这样)？

原创

我正在做一个由simon HAXL pt1的乐趣给oracle/docker的haxl示例的端口--作为概念的证明。

我正在使用现有的sql脚本来生成db (在现实世界中，我的db表不在我手中)--我有以下的db布局

表后信息

| POSTID NUMBER | POSTDATE DATE | POSTTOPIC VARCHAR2(512 CHAR) |

表后内容

| POSTID NUMBER | CONTENT CLOB |

表后视图

| POSTID NUMBER | VIEWS INT |

当然，我想表达的关系是，POSTID是postcontent中的一个外键&在相应的haskell持久QuasiQuoter中是postview中的唯一键。在是书之后，维基和测试用例从wiki链接起来。

我创建了以下模板haskell拼接：

share [ mkPersist sqlSettings {mpsGeneric = False} , mkMigrate "compositeMigrate" , mkDeleteCascade sqlSettings {mpsGeneric = False}] [persistUpperCase|

Post sql=POSTINFO
  Id Int sql=POSTID
  date UTCTime sql=POSTDATE
  topic Text sql=POSTTOPIC

  deriving Show Eq

PostContent sql=POSTCONTENT
  Id PostId sql=POSTID
  content Text sql=CONTENT
  deriving Show Eq

PostViews sql=POSTVIEWS
  Id PostId sql=POSTID
  views Int sql=VIEWS
  deriving Show Eq
|]

，它使用错误进行编译。

error:
    • Not in scope: type constructor or class ‘PostId’
    • In the quasi-quotation:
        [persistUpperCase|

Post sql=POSTINFO
  Id Int sql=POSTID
  date UTCTime sql=POSTDATE
  topic Text sql=POSTTOPIC

  deriving Show Eq

PostContent
  Id PostId sql=POSTID
  content Text sql=CONTENT
  deriving Show Eq

PostViews
  Id PostId sql=POSTID
  views Int sql=VIEWS
  deriving Show Eq
|]

有一点要注意的是，下面的测试用例是准商工作的，

  Citizen
    name String
    age Int Maybe
    deriving Eq Show
  Address
    address String
    country String
    deriving Eq Show
  CitizenAddress
    citizen CitizenId
    address AddressId
    Primary citizen address
    deriving Eq Show

下面是一个只运行错误和一些工作版本的最小示例(并相应地更改#define行)

> stack runhaskell --package persistent-template minimal.hs

minimal.hs

{-# LANGUAGE FlexibleInstances          #-}
{-# LANGUAGE GADTs                      #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses      #-}
{-# LANGUAGE QuasiQuotes                #-}
{-# LANGUAGE TemplateHaskell            #-}
{-# LANGUAGE TypeFamilies               #-}
{-# LANGUAGE CPP                        #-}

module Minimal where

import Database.Persist.TH

#define FAILS
main :: IO ()
main = putStrLn "It works"


#ifdef WORKS
share [ mkPersist sqlSettings {mpsGeneric = False} , mkMigrate "compositeMigrate" , mkDeleteCascade sqlSettings {mpsGeneric = False}] [persistUpperCase|

Post sql=POSTINFO
  Id Int sql=POSTID
  topic String sql=POSTTOPIC

  deriving Show Eq
|]
#endif

#ifdef ALSOWORKS
share [ mkPersist sqlSettings {mpsGeneric = False} , mkMigrate "compositeMigrate" , mkDeleteCascade sqlSettings {mpsGeneric = False}] [persistUpperCase|

Post sql=POSTINFO
  Id Int sql=POSTID
  topic String sql=POSTTOPIC

  deriving Show Eq


PostContent sql=POSTCONTENT
  post PostId sql=POSTID
  content String sql=POSTCONTENT

  deriving Show Eq
|]
#endif

#ifdef FAILS
share [ mkPersist sqlSettings {mpsGeneric = False} , mkMigrate "compositeMigrate" , mkDeleteCascade sqlSettings {mpsGeneric = False}] [persistUpperCase|

Post sql=POSTINFO
  Id Int sql=POSTID
  topic String sql=POSTTOPIC

  deriving Show Eq

PostContent sql=POSTCONTENT
  Id PostId sql=POSTID
  content String sql=POSTCONTENT

  deriving Show Eq
|]
#endif

-- UPDATE

#ifdef FAILSTOO
share [ mkPersist sqlSettings {mpsGeneric = False} , mkMigrate "compositeMigrate" , mkDeleteCascade sqlSettings {mpsGeneric = False}] [persistUpperCase|

Post
  topic String

  deriving Show Eq

PostContent
  Id PostId
  content String

  deriving Show Eq
|]
#endif

Answer 1

我可以用持久的方式表示主键是外键吗？

是。假设Sqlite作为数据库的示例代码示例：

#!/usr/bin/env stack
{- stack
     --resolver lts-7.14
     --install-ghc
     runghc
     --package yesod
     --package yesod-core
     --package blaze-html
     --package text
     --package persistent
     --package persistent-template
     --package persistent-sqlite
     --package shakespeare
     --package aeson
-}

{-# LANGUAGE EmptyDataDecls #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}

import Control.Monad.IO.Class (liftIO)
import Control.Monad.Logger (runStderrLoggingT)
import Database.Persist
import Database.Persist.Sqlite
import Database.Persist.TH

share
  [mkPersist sqlSettings, mkMigrate "migrateAll"]
  [persistLowerCase|
Post
    topic String
    deriving Show 
PostContent
    pid PostId
    Primary pid
    deriving Show
|]

main :: IO ()
main = mockMigration migrateAll

在执行时，您可以得到以下内容：

CREATE TABLE "post"("id" INTEGER PRIMARY KEY,"topic" VARCHAR NOT NULL)
CREATE TABLE "post_content"("pid" INTEGER NOT NULL REFERENCES "post", PRIMARY KEY ("pid"))

在上面的示例中可以看到，表post_content中的post_content列既是主键，也是外键。