I know I can do the conversion using fromPGArray but I was hoping to use the fromRow instances to remove some of the boilerplate.
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 10:52:46AM +0000, 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 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]}]}}]
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