46 lines
1.1 KiB
Haskell
46 lines
1.1 KiB
Haskell
module ChuSQL.Model (Column (..), Value (..), Row, Table (..), Database, colNames, colType, lookupTable, allColumns) where
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-- 列的类型
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data Column
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= TInt
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| TStr
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| TBool
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deriving (Show, Eq)
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-- 列的值：整数、字符串、布尔
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data Value
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= VInt Int
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| VStr String
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| VBool Bool
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deriving (Show, Eq)
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-- 一行：列名 → 值
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type Row = [(String, Value)]
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-- 一张表
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data Table = Table
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{ tableName :: String
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, tableCols :: [(String, Column)]
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, tableRows :: [Row]
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}
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deriving (Show)
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-- 数据库：多张表
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type Database = [(String, Table)]
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-- 获取列名
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colNames :: Table -> [String]
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colNames = map fst . tableCols
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-- | 查某一列的类型
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colType :: Table -> String -> Maybe Column
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colType t c = lookup c (tableCols t)
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-- | 按名字查表；表不存在就报错
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lookupTable :: Database -> String -> Either String Table
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lookupTable db t = maybe (Left ("unknown table: " ++ t)) Right (lookup t db)
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-- | 投影列清单里的哨兵值：它表示"全部列，不用挑"，不是列名
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allColumns :: String
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allColumns = "*"
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