82 lines
3.0 KiB
Haskell
82 lines
3.0 KiB
Haskell
module ChuSQL.Storage.Memory (MemoryStorage (runMemoryStorage)) where
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import ChuSQL.Model
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import ChuSQL.Storage
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-- 内存实现：Database 上的状态，错误通道是 Either String。
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newtype MemoryStorage a = MemoryStorage {runMemoryStorage :: Database -> Either String (a, Database)}
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instance Functor MemoryStorage where
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fmap f (MemoryStorage m) = MemoryStorage $ \db -> do
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(a, db') <- m db
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Right (f a, db')
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instance Applicative MemoryStorage where
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pure x = MemoryStorage $ \db -> Right (x, db)
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MemoryStorage mf <*> MemoryStorage ma = MemoryStorage $ \db -> do
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(f, db1) <- mf db
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(a, db2) <- ma db1
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Right (f a, db2)
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instance Monad MemoryStorage where
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MemoryStorage m >>= k = MemoryStorage $ \db -> do
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(a, db') <- m db
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runMemoryStorage (k a) db'
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instance MonadStorage MemoryStorage where
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-- \| 全表扫描
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scan t = MemoryStorage $ \db -> do
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tbl <- lookupTable db t
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Right (Right (tableRows tbl), db)
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-- \| 追加一行
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insert t r = MemoryStorage $ \db -> do
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tbl <- lookupTable db t
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Right (Right (), replaceTable t tbl{tableRows = tableRows tbl ++ [r]} db)
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-- \| 整表替换
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replaceAll t rows = MemoryStorage $ \db -> do
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tbl <- lookupTable db t
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Right (Right (), replaceTable t tbl{tableRows = rows} db)
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-- \| 建空表；已存在报错
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createTable name cols = MemoryStorage $ \db ->
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if any ((== name) . fst) db
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then Right (Left ("table already exists: " ++ name), db)
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else Right (Right (), db ++ [(name, Table name cols [])])
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-- \| 删表；不存在报错
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dropTable name = MemoryStorage $ \db ->
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if any ((== name) . fst) db
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then Right (Right (), filter ((/= name) . fst) db)
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else Right (Left ("unknown table: " ++ name), db)
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-- \| 删一列：表定义里去掉这一列，每一行里的那一格也一起去掉
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dropColumn name col = MemoryStorage $ \db ->
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case lookup name db of
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Nothing -> Right (Left ("unknown table: " ++ name), db)
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Just tbl ->
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if col `notElem` map fst (tableCols tbl)
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then Right (Left ("unknown column: " ++ col), db)
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else
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Right
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( Right ()
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, replaceTable
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name
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tbl
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{ tableCols = filter ((/= col) . fst) (tableCols tbl)
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, tableRows = map (filter ((/= col) . fst)) (tableRows tbl)
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}
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db
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)
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-- \| 原样返回当前库
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snapshot = MemoryStorage $ \db -> Right (db, db)
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-- | 用给定表替换同名表
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replaceTable :: String -> Table -> Database -> Database
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replaceTable name table =
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map (\(n, t) -> if n == name then (n, table) else (n, t))
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