Yesod Single RawSql and Return it as JSON Format

Question

hope you help me with this.

i have a rawSql:

latestPrice :: Handler [(Single PricesId, Single PersistValue, Single    PersistValue, Single PersistValue, Single PersistValue, Single PersistValue)]
latestPrice = do
  runDB $ rawSql qryStr []
        where qryStr = " SELECT prices.id,\
                            \CONCAT(cities.name, '(', states.code, '), ', countries.name) as city, \
                            \prices.s_id, \
                            \prices.s_name, \
                            \prices.quality, \
                            \AVG(prices.amount) as amount \
                    \FROM prices \
                    \INNER JOIN cities ON cities.id = prices.city_id \
                    \INNER JOIN states ON states.id = cities.state_id \
                    \INNER JOIN countries ON countries.id = states.country_id \
                    \WHERE prices.city_id > 0 \
                    \GROUP BY prices.id, city, prices.strain_id, prices.strain_name, prices.quality, prices.quality;";

and i have a handler that call that function and should return a JSON Format:

getLatestPriceSubmissionR:: Handler (Value)
getLatestPriceSubmissionR  = do
    results <- latestPrice
    return map (
     \(Single id, Single city, Single s_name, Single strain_id, Single quality, Single amount) -> [ "id" .= id,"city" .=  city,"s_id" .=  s_id,"s_name" .=  s_name, "quality" .= quality,"amount" .= amount ]
   ) results

my question is: does my code in Handler getLatestPriceSubmissionR is correct? it does give me only a warning message not an error message:

Couldn't match type [[aeson-0.8.0.0:Data.Aeson.Types.Internal.Pair]]
          with Value
Expected type: HandlerT App IO Value
Actual type: HandlerT
             App IO [[aeson-0.8.0.0:Data.Aeson.Types.Internal.Pair]] …

also

No instance for (ToTypedContent [Value])
arising from a use of yesodRunner

Hope you help me.

thank you in advance

Answer 1

The line

return map (\(...) -> [ ... ]) results

looks wrong, you probably mean

return $ map (\(...) -> [ ... ]) results

Also, this returns a list of lists, which is not a Value as in the type signature.

Further, this is an error, not a warning:

Couldn't match type [[aeson-0.8.0.0:Data.Aeson.Types.Internal.Pair]]
          with Value
Expected type: HandlerT App IO Value
Actual type: HandlerT
             App IO [[aeson-0.8.0.0:Data.Aeson.Types.Internal.Pair]] …