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Today's Topics:
1. Re: database access,extracting result... (Damien Mattei)
2. Re: database access,extracting result... (David McBride)
----------------------------------------------------------------------
Message: 1
Date: Mon, 3 Dec 2018 15:40:39 +0100
From: Damien Mattei <mat...@oca.eu>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] database access,extracting result...
Message-ID: <5c054067.3090...@oca.eu>
Content-Type: text/plain; charset=utf-8
just find myself this solution:
main :: IO ()
main =
do
conn <- connect defaultConnectInfo
{ connectHost = "moita",
connectUser = "mattei",
connectPassword = "****",
connectDatabase = "sidonie" }
rows <- query_ conn "select `N° BD` from sidonie.Coordonnées where
Nom = 'A 20'"
forM_ rows $ \(Only a) ->
putStrLn $ Text.unpack a
Le 03/12/2018 12:21, Damien Mattei a écrit :
> {-# LANGUAGE OverloadedStrings #-}
>
> import Database.MySQL.Simple
> import Control.Monad
> import Data.Text as Text
> import Data.Int
>
>
> main :: IO ()
> main = do
> conn <- connect defaultConnectInfo
> { connectHost = "moita",
> connectUser = "mattei",
> connectPassword = "******",
> connectDatabase = "sidonie" }
>
> rows <- query_ conn "select `N° BD` from sidonie.Coordonnées where Nom
> = 'A 20'"
>
> --putStrLn $ show rows
>
> forM_ rows $ \(fname, lname) ->
> putStrLn $ fname ++ " " ++ Text.unpack lname ++ " "
>
>
> here is the error:
>
> *Main> :load Toto
> [1 of 1] Compiling Main ( Toto.hs, interpreted )
> Ok, one module loaded.
> *Main> main
> *** Exception: ConversionFailed {errSQLType = "1 values:
> [(VarString,Just \"-04.3982\")]", errHaskellType = "2 slots in target
> type", errFieldName = "[\"N\\194\\176 BD\"]", errMessage = "mismatch
> between number of columns to convert and number in target type"}
>
> -04.3982 is the values i want to put in a variable,it's the N° BD
> (Durchmusterung Number)
>
>
> ???
>
> any help greatly appeciated ;-)
>
>
--
damien.mat...@unice.fr, damien.mat...@oca.eu, UNS / OCA / CNRS
------------------------------
Message: 2
Date: Mon, 3 Dec 2018 09:42:11 -0500
From: David McBride <toa...@gmail.com>
To: Haskell Beginners <beginners@haskell.org>
Subject: Re: [Haskell-beginners] database access,extracting result...
Message-ID:
<CAN+Tr43X5L6sQ7nxQhuxfMWXdh1610MEeqhb8XTsBY_b6Ua=o...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Here's how it works, every time you supply a query, you supply the
parameters to the query in a tuple. Furthermore the results can be gotten
back as a tuple by type hinting each value. Warning: I have not run this
code, but it should be close.
query "select age, is_old from user where uid = ? and name = ? (uid :: Int,
name :: String) :: IO [(Integer, Bool)]
But what happens when you want to supply a single parameter (or receive a
single value?)
query "select * from user where uid = ?" (uid)
The problem with that is (uid) is not a tuple. It's just an integer in
parenthesis. There in fact is no way to specify a tuple of one length. So
mysql-simple (and other libraries) very often have a single type meant to
be used as a single element tuple. In mysql-simple's (and
postgresql-simple) case that is the (Only a) type. (Side note, I wish
these were in the standard Tuple module, as this comes once in awhile).
query "select name from user where uid = ?" (Only uid) :: IO [Only String]
Remember that you can also make your own records implement the QueryParams and
QueryResults classes so that you can write
On Mon, Dec 3, 2018 at 6:22 AM Damien Mattei <mat...@oca.eu> wrote:
> {-# LANGUAGE OverloadedStrings #-}
>
> import Database.MySQL.Simple
> import Control.Monad
> import Data.Text as Text
> import Data.Int
>
>
> main :: IO ()
> main = do
> conn <- connect defaultConnectInfo
> { connectHost = "moita",
> connectUser = "mattei",
> connectPassword = "******",
> connectDatabase = "sidonie" }
>
> rows <- query_ conn "select `N° BD` from sidonie.Coordonnées where Nom
> = 'A 20'"
>
> --putStrLn $ show rows
>
> forM_ rows $ \(fname, lname) ->
> putStrLn $ fname ++ " " ++ Text.unpack lname ++ " "
>
>
> here is the error:
>
> *Main> :load Toto
> [1 of 1] Compiling Main ( Toto.hs, interpreted )
> Ok, one module loaded.
> *Main> main
> *** Exception: ConversionFailed {errSQLType = "1 values:
> [(VarString,Just \"-04.3982\")]", errHaskellType = "2 slots in target
> type", errFieldName = "[\"N\\194\\176 BD\"]", errMessage = "mismatch
> between number of columns to convert and number in target type"}
>
> -04.3982 is the values i want to put in a variable,it's the N° BD
> (Durchmusterung Number)
>
>
> ???
>
> any help greatly appeciated ;-)
>
>
> --
> damien.mat...@unice.fr, damien.mat...@oca.eu, UNS / OCA / CNRS
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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