Class.hs

{-# LANGUAGE TypeFamilies #-}
module Database.Persist.Audit.Class where

import           Data.Text              (Text)
import           Data.Time              (UTCTime)
import           Database.Persist.Types
import           Database.Persist.Audit.Types


-- | Persistent Model types that have a corresponding Audit type as produced by 'Database.Persist.Audit.Generator.generateAuditModels'
-- need to implement 'ToAudit' in order to use the queries
-- from 'Database.Persist.Audit.Queries'. Given the following two Persistent models:
-- 
-- @
-- Person
--   name String
--   age Int Maybe
--
-- PersonAudit
--   name String
--   age Int Maybe
--   originalId PersonId noreference
--   auditAction AuditAction
--   editedBy Text
--   editedOn UTCTime
-- 
-- @
--
-- The 'ToAudit' instance should look like this:
-- 
-- @
-- instance ToAudit Person where
--  type AuditResult Person = PersonAudit
--  toAudit v k auditAction editedBy editedOn = PersonAudit (personName v)
--                                                          (personAge v)
--                                                          k auditAction editedBy editedOn 
-- @
-- 
-- 'Database.Persist.Audit.Generator.generateAuditModels' can help automate these instances.
class ToAudit a where
  type AuditResult a :: *
  toAudit :: a -> Key a -> AuditAction -> Text -> UTCTime -> AuditResult a