Thank you for pointing me in the right way. This does almost what I want. However I want to end up with a [[Double]] rather than (PGArray (PGArray Double)). I know I can do the conversion using fromPGArray but I was hoping to use the fromRow instances to remove some of the boilerplate. So I have: data IIM = IIM {key :: String ,itype :: String ,idet :: Maybe String ,imat :: (PGArray (PGArray Double))} deriving (Read, Show, Eq) instance FromRow IIM where fromRow = IIM <$> field <*> field <*> field <*> field Which works fine, but I would actually like my data IIM to be: data IIM = IIM {key :: String ,itype :: String ,idet :: Maybe String ,imat :: [[Double]]} deriving (Read, Show, Eq) But I can't figure out how to get a fromRow instance for that, otherwise I need to return SQL results in a (,,,,) and then create the IIM from that which seems a lot of extra typing. PS. I started looking into Opaleye as a possible DSL and would appreciate any help you can give me in figuring out how to represent arrays in that. I am assuming I need to do something with queryRunnerColumn but I was not able to understand the example. On Friday, December 26, 2014 10:02:21 PM UTC+11, Tom Ellis wrote:
On Fri, Dec 26, 2014 at 02:36:07PM +1100, Riaan wrote:
So went back to HDBC. But now my queries are starting to get fairly long and I have been looking at libraries like Persistent with Esqualeto, HaskellDB and Groundhog to make my queries a little more composable and type safe.
Don't forget to look at Opaleye too :) It doesn't really have much support for arrays at the moment, but if you let me know what you want to do I'm happy to help you.
So to my question. Does anyone have experience with one of these
On Fri, Dec 26, 2014 at 10:52:46AM +0000, Tom Ellis wrote: libraries
in dealing with postgresql arrays
postgresql-simple has
instance (FromField a, Typeable a) => FromField (PGArray a)
Does that not do exactly what you want?
import Database.PostgreSQL.Simple (query_, ConnectInfo(..), connect, Only) import Database.PostgreSQL.Simple.Types (PGArray)
import Data.String (fromString)
connectInfo :: ConnectInfo connectInfo = ConnectInfo { connectHost = "localhost" , connectPort = 25433 , connectUser = "tom" , connectPassword = "tom" , connectDatabase = "opaleye_test" }
arrayQuery :: String arrayQuery = "select '{{1,2}, {3,4}}' :: integer[][]"
main :: IO () main = do conn <- connect connectInfo results <- query_ conn (fromString arrayQuery) :: IO [Only (PGArray (PGArray Int))] print results
-- Output -- -- ghci> main -- [Only {fromOnly = PGArray {fromPGArray = [PGArray {fromPGArray = [1,2]},PGArray {fromPGArray = [3,4]}]}}] _______________________________________________ Haskell-Cafe mailing list Haskel...@haskell.org javascript: http://www.haskell.org/mailman/listinfo/haskell-cafe