Haskell Persistent Database Primary Key

Question

When using the following code, I don't want to use the default database key. Intead, I plan to generate a hashcode from a piece of information and use it as a key. How should I use such a key?

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|
Person
    name String
    age Int Maybe
    deriving Show
BlogPost
    title String
    authorId PersonId
    deriving Show
|]

Answer 1

A code demonstrating such an idea:

#!/usr/bin/env stack
{- stack
     --resolver lts-7.14
     --install-ghc
     runghc
     --package persistent
     --package persistent-template
     --package persistent-sqlite
-}

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

import Database.Persist
import Database.Persist.Sqlite
import Database.Persist.TH

share
  [mkPersist sqlSettings, mkMigrate "migrateAll"]
  [persistLowerCase|
Blogpost
    topic String
    hash String
    Primary hash
    deriving Show 
|]

main :: IO ()
main = mockMigration migrateAll

Note that above code will produce this output:

CREATE TABLE "blogpost"("topic" VARCHAR NOT NULL,"hash" VARCHAR NOT NULL, PRIMARY KEY ("hash"))

You can see how the primary key of the blogpost table is hash