[Haskell-beginners] Database.SQLite.Simple: Select query with more than 10 elements tuple

Miro Karpis miroslav.karpis at gmail.com
Tue Dec 24 00:37:45 UTC 2013


Hi, please ... I need help with following:

I have a table with 11 columns. I would like to create a query where in
return I should get values of all columns. Problem is that when I try with
10 elements everything works OK. With 11 I will get compile error.

I found in the Database.SQLite.Simple documentation following:
A collection type that can be converted from a sequence of fields.
Instances are provided for tuples up to 10 elements and lists of any length.

So is it possible to select more than 10 columns in one query? It must be
right?


working code:
-------------------------
queryX :: Query
queryX = "SELECT el1, el2, el3, el4, el5, el6, el7, el8, el9, el10 FROM
tableX"

saveBtceTickerData :: IO ()
saveBtceTickerData = do
    conn <- open "../mydb.sqlite"
    r <- query_ conn queryX :: IO [(Double, Int, Double, Double, Double,
Double, Double, Double, Double, Double)]
    mapM_ print r
    close conn
    putStrLn "done"


non-working code:
-------------------------
someQuery :: Query
someQuery = "SELECT el1, el2, el3, el4, el5, el6, el7, el8, el9, el10, el11
FROM tableX"

saveBtceTickerData :: IO ()
saveBtceTickerData = do
    conn <- open "../mydb.sqlite"
    r <- query_ conn queryX :: IO [(Double, Int, Double, Double, Double,
Double, Double, Double, Double, Double, Double)]
    mapM_ print r
    close conn
    putStrLn "done"

------
Error output:

No instance for (FromRow

                       (Double,

                        Int,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double))

      arising from a use of `query_'

    Possible fix:

      add an instance declaration for

      (FromRow

         (Double,

          Int,

          Double,

          Double,

          Double,

          Double,

          Double,

          Double,

          Double,

          Double,

          Double))


thanks,
m.
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