用Haskell中的参数更新Sqlite3

Question

最近我开始使用haskell中的sqlite3工作，我想知道如何使用参数作为偏移量修改表中的变量？

我愿做这样的事情：

execute_ conn "CREATE TABLE IF NOT EXISTS test (id INTEGER PRIMARY KEY, v INTEGER)" 

execute conn "INSERT INTO test (v) VALUES (?)" (Only ("1" :: String)) 

execute conn "UPDATE test SET v = v + ?" (Only modifyingValue) <--- this is not working 

谢谢。

Answer 1

这里是关于ErrorMisuse错误信息：

https://www.sqlite.org/cvstrac/wiki?p=LibraryRoutineCalledOutOfSequence

也许连接已经关闭？或者你在两个不同的线程中使用相同的连接？

下面是一些示例代码的工作原理：

{-# LANGUAGE OverloadedStrings #-} 

import   Control.Applicative 
import qualified Data.Text as T 
import   Database.SQLite.Simple 
import   Database.SQLite.Simple.FromRow 

dumpTable conn table = do 
    r <- query_ conn "SELECT * from test" :: IO [(Int,String,Int)] 
    mapM_ print r 

main :: IO() 
main = do 
    conn <- open "test.db" 
    execute_ conn "CREATE TABLE IF NOT EXISTS test (id INTEGER PRIMARY KEY, firstname TEXT, pets INTEGER)" 
    execute conn "INSERT INTO test (firstname, pets) VALUES (?,?)" 
       ("Alice" :: String, 2 :: Int) 
    execute conn "INSERT INTO test (firstname, pets) VALUES (?,?)" 
       ("Bob" :: String, 3 :: Int) 
    putStrLn "before:" 
    dumpTable conn "test" 
    execute conn "UPDATE TEST SET pets = pets + ?" (Only (4 :: Int)) 
    putStrLn "after:" 
    dumpTable conn "test" 
    close conn