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{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE DuplicateRecordFields #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE TypeOperators #-}
-- | Breaking changes to this module are not reflected in the major version
-- number. Prefer to import from "Database.Persist.Sql" instead. If you neeed
-- something from this module, please file an issue on GitHub.
module Database.Persist.Sql.Types.Internal
( HasPersistBackend (..)
, IsPersistBackend (..)
, SqlReadBackend (..)
, SqlWriteBackend (..)
, readToUnknown
, readToWrite
, writeToUnknown
, LogFunc
, InsertSqlResult (..)
, Statement (..)
, IsolationLevel (..)
, makeIsolationLevelStatement
, SqlBackend (..)
, SqlBackendCanRead
, SqlBackendCanWrite
, SqlReadT
, SqlWriteT
, IsSqlBackend
, SqlBackendHooks (..)
) where
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.Reader (ReaderT, ask, runReaderT)
import Database.Persist.Class
( BackendCompatible(..)
, HasPersistBackend(..)
, PersistQueryRead
, PersistQueryWrite
, PersistStoreRead
, PersistStoreWrite
, PersistUniqueRead
, PersistUniqueWrite
)
import Database.Persist.Class.PersistStore (IsPersistBackend(..))
import Database.Persist.SqlBackend.Internal
import Database.Persist.SqlBackend.Internal.InsertSqlResult
import Database.Persist.SqlBackend.Internal.IsolationLevel
import Database.Persist.SqlBackend.Internal.MkSqlBackend
import Database.Persist.SqlBackend.Internal.Statement
-- | An SQL backend which can only handle read queries
--
-- The constructor was exposed in 2.10.0.
newtype SqlReadBackend = SqlReadBackend { unSqlReadBackend :: SqlBackend }
instance HasPersistBackend SqlReadBackend where
type BaseBackend SqlReadBackend = SqlBackend
persistBackend = unSqlReadBackend
instance IsPersistBackend SqlReadBackend where
mkPersistBackend = SqlReadBackend
-- | An SQL backend which can handle read or write queries
--
-- The constructor was exposed in 2.10.0
newtype SqlWriteBackend = SqlWriteBackend { unSqlWriteBackend :: SqlBackend }
instance HasPersistBackend SqlWriteBackend where
type BaseBackend SqlWriteBackend = SqlBackend
persistBackend = unSqlWriteBackend
instance IsPersistBackend SqlWriteBackend where
mkPersistBackend = SqlWriteBackend
-- | Useful for running a write query against an untagged backend with unknown capabilities.
writeToUnknown :: Monad m => ReaderT SqlWriteBackend m a -> ReaderT SqlBackend m a
writeToUnknown ma = do
unknown <- ask
lift . runReaderT ma $ SqlWriteBackend unknown
-- | Useful for running a read query against a backend with read and write capabilities.
readToWrite :: Monad m => ReaderT SqlReadBackend m a -> ReaderT SqlWriteBackend m a
readToWrite ma = do
write <- ask
lift . runReaderT ma . SqlReadBackend $ unSqlWriteBackend write
-- | Useful for running a read query against a backend with unknown capabilities.
readToUnknown :: Monad m => ReaderT SqlReadBackend m a -> ReaderT SqlBackend m a
readToUnknown ma = do
unknown <- ask
lift . runReaderT ma $ SqlReadBackend unknown
-- | A constraint synonym which witnesses that a backend is SQL and can run read queries.
type SqlBackendCanRead backend =
( BackendCompatible SqlBackend backend
, PersistQueryRead backend, PersistStoreRead backend, PersistUniqueRead backend
)
-- | A constraint synonym which witnesses that a backend is SQL and can run read and write queries.
type SqlBackendCanWrite backend =
( SqlBackendCanRead backend
, PersistQueryWrite backend, PersistStoreWrite backend, PersistUniqueWrite backend
)
-- | Like @SqlPersistT@ but compatible with any SQL backend which can handle read queries.
type SqlReadT m a = forall backend. (SqlBackendCanRead backend) => ReaderT backend m a
-- | Like @SqlPersistT@ but compatible with any SQL backend which can handle read and write queries.
type SqlWriteT m a = forall backend. (SqlBackendCanWrite backend) => ReaderT backend m a
-- | A backend which is a wrapper around @SqlBackend@.
type IsSqlBackend backend =
( IsPersistBackend backend
, BaseBackend backend ~ SqlBackend
)
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