63 lines
2.5 KiB
Haskell
63 lines
2.5 KiB
Haskell
{-# LANGUAGE NoImplicitPrelude #-}
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{-# LANGUAGE OverloadedStrings #-}
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{-# LANGUAGE TypeFamilies, FlexibleContexts, ConstraintKinds #-}
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{-# LANGUAGE QuasiQuotes #-}
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module Utils.DB where
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import ClassyPrelude.Yesod
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import qualified Data.List as List
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import Data.Map (Map)
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import qualified Data.Map as Map
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-- import Database.Persist -- currently not needed here
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entities2map :: PersistEntity record => [Entity record] -> Map (Key record) record
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entities2map = foldl' (\m entity -> Map.insert (entityKey entity) (entityVal entity) m) Map.empty
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getKeyBy :: (PersistEntityBackend record ~ BaseBackend backend, PersistEntity record, PersistUniqueRead backend, MonadIO m)
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=> Unique record -> ReaderT backend m (Maybe (Key record))
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getKeyBy u = (fmap entityKey) <$> getBy u -- TODO optimize this, so that DB does not deliver entire record!
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getKeyBy404 :: (PersistEntityBackend record ~ BaseBackend backend, PersistEntity record, PersistUniqueRead backend, MonadIO m)
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=> Unique record -> ReaderT backend m (Key record)
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getKeyBy404 = (fmap entityKey) . getBy404 -- TODO optimize this, so that DB does not deliver entire record!
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existsBy :: (PersistEntityBackend record ~ BaseBackend backend, PersistEntity record, PersistUniqueRead backend, MonadIO m)
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=> Unique record -> ReaderT backend m Bool
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existsBy = fmap isJust . getBy
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myReplaceUnique -- Identical to Database.Persist.Class, except for the better type signature (original requires Eq record which is not needed anyway)
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:: (MonadIO m
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,Eq (Unique record)
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,PersistRecordBackend record backend
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,PersistUniqueWrite backend)
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=> Key record -> record -> ReaderT backend m (Maybe (Unique record))
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myReplaceUnique key datumNew = getJust key >>= replaceOriginal
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where
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uniqueKeysNew = persistUniqueKeys datumNew
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replaceOriginal original = do
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conflict <- checkUniqueKeys changedKeys
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case conflict of
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Nothing -> replace key datumNew >> return Nothing
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(Just conflictingKey) -> return $ Just conflictingKey
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where
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changedKeys = uniqueKeysNew List.\\ uniqueKeysOriginal
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uniqueKeysOriginal = persistUniqueKeys original
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checkUniqueKeys
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:: (MonadIO m
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,PersistEntity record
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,PersistUniqueRead backend
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,PersistRecordBackend record backend)
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=> [Unique record] -> ReaderT backend m (Maybe (Unique record))
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checkUniqueKeys [] = return Nothing
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checkUniqueKeys (x:xs) = do
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y <- getBy x
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case y of
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Nothing -> checkUniqueKeys xs
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Just _ -> return (Just x)
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