Hello, haskellers!
Here is HDBI-1.2 and some friends
There is class `FromRow` and `ToRow` from this version as well as
hdbi-conduit package. So, you can write your code like this:
{-# LANGUAGE
OverloadedStrings
, TemplateHaskell
#-}
import Control.Monad.IO.Class
import Data.Conduit
import Data.Conduit.HDBI
import Database.HDBI
import Database.HDBI.SQlite
import Language.Haskell.TH.HDBI
import qualified Data.Conduit.List as L
import qualified Data.Text as T
data Animal = Animal
{ aName :: T.Text
, aAge :: Double
, aWeight :: Double
}
$(deriveFromRow ''Animal)
$(deriveToRow ''Animal)
animalsList :: [Animal]
animalsList = [Animal "Puffy" 15 0.3
,Animal "Puppy" 1 0.5
,Animal "Rex" 3 5
,Animal "Cat" 2 2.2]
foldAnimals :: (Animal, Animal, Double) -> Animal -> (Animal, Animal, Double)
foldAnimals (a, b, sumw) c@(Animal name age weight) = (newa, newb, sumw + weight)
where
newa | age > (aAge a) = c
| otherwise = a
newb | weight > (aWeight b) = c
| otherwise = b
main = do
(aged, weighted, wsum) <- runResourceT $ do
(_, c) <- allocConnection $ connectSqlite3 ":memory:"
liftIO $ do
runRaw c "create table animals (name, age, weight)"
runManyRows c "insert into animals(name, age, weight) values (?,?,?)" animalsList
selectRawAllRows c "select name, age, weight from animals"
$$ L.fold foldAnimals (none, none, 0)
putStrLn $ "The most aged is " ++ (T.unpack $ aName aged)
++ " with age " ++ (show $ aAge aged)
putStrLn $ "The most weighted is " ++ (T.unpack $ aName weighted)
++ " with weigh " ++ (show $ aWeight weighted)
putStrLn $ "Total biomass is " ++ show wsum
where
none = Animal "" 0 0
the result will be:
The most aged is Puffy with age 15.0
The most weighted is Rex with weigh 5.0
Total biomass is 8.0
This is much more type safe way to work with raw SQL queries.
Links:
http://hackage.haskell.org/package/hdbi
http://hackage.haskell.org/package/hdbi-postgresql
http://hackage.haskell.org/package/hdbi-sqlite
http://hackage.haskell.org/package/hdbi-conduit
And you are welcome on GitHub:
https://github.com/s9gf4ult/hdbi
https://github.com/s9gf4ult/hdbi-postgresql
https://github.com/s9gf4ult/hdbi-sqlite
https://github.com/s9gf4ult/hdbi-conduit
--
Aleksey Uymanov