I'm working on my first Haskell web app, and am having trouble converting a BSON document into JSON and then sending it as an API response. I'm currently using the AesonBson package to convert my BSON to an Aeson Object, but can't figure out how to send that Aeson Object as a JSON API response.
Here is an example of a route handler in my server:
{-# LANGUAGE OverloadedStrings #-}
module Web.Routes where
import Web.Scotty
import Web.Utils
import Web.Actions.Database
import Control.Monad.Trans (liftIO)
import Data.AesonBson
routes :: ScottyM ()
routes = do
get "/databases/:db/:collection" $ do
db <- param "db"
collection <- param "collection"
docs <- liftIO $ getAllDocuments "127.0.0.1" db collection
json $ map aesonify docs
These seems like it should be simple - getAllDocuments returns IO [Document], and then I map aesonfy over my list of docs, before attempting to return them as a JSON server response.
Problem is I keep getting this No instance for ToJSON error:
No instance for (aeson-0.8.0.2:Data.Aeson.Types.Class.ToJSON
aeson-0.6.2.1:Data.Aeson.Types.Internal.Value)
arising from a use of ‘Web.Scotty.json’
In the expression: Web.Scotty.json
In a stmt of a 'do' block:
Web.Scotty.json
GHC.Base.$ GHC.Base.map Data.AesonBson.aesonify docs
In the second argument of ‘(GHC.Base.$)’, namely
‘do { db <- Web.Scotty.param "db";
collection <- Web.Scotty.param "collection";
docs <- transformers-0.3.0.0:Control.Monad.IO.Class.liftIO
GHC.Base.$
Web.Actions.Database.getAllDocuments "127.0.0.1" db collection;
Web.Scotty.json
GHC.Base.$ GHC.Base.map Data.AesonBson.aesonify docs }’
Any idea what I am missing? It looks like aesonify returns an Aeson Object... shouldn't that be an instace of ToJSON? Any help would be greatly appreciated, I've been spinning my wheels on this one for a while now. I've tried placing Aeson's object function in different places, manually adding documents as an instance of ToJSON, but really can't figure this out.
