Danielle McLean
02fd91cb77
Different areas of the app need access to entities - for example both the entry handler needs the entry itself to render it, but the breadcrumbs also need the entry to decide what to label its breadcrumb. Previously this was achieved by fetching entities from the database twice. This sucks, so now it's implemented by fetching entities once and caching them using Yesod's per-request cache.
24 lines
1 KiB
Haskell
24 lines
1 KiB
Haskell
{-# LANGUAGE DeriveDataTypeable #-}
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{-# LANGUAGE FlexibleContexts #-}
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{-# LANGUAGE TypeFamilies #-}
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module Model.Cache ( getCached ) where
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import Data.Typeable ( Typeable )
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import Database.Persist ( Entity (..), Key (..), PersistStore, PersistRecordBackend, keyToValues )
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import Yesod ( MonadHandler, HandlerSite, YesodPersist, YesodPersistBackend, cachedBy, get404, liftHandlerT, runDB )
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import qualified Data.ByteString.Char8 as C
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newtype CachedEntity t = CachedEntity { unCachedEntity :: Entity t } deriving Typeable
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getCached :: ( MonadHandler m
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, YesodPersist (HandlerSite m)
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, PersistStore (YesodPersistBackend (HandlerSite m))
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, PersistRecordBackend entity (YesodPersistBackend (HandlerSite m))
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, Typeable entity
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) => Key entity -> m (Entity entity)
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getCached entId = liftHandlerT . cached . runDB . withId . get404 $ entId
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where key = C.pack . show . keyToValues $ entId
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withId = fmap $ Entity entId
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cached = fmap unCachedEntity . cachedBy key . fmap CachedEntity
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