What is a correct way of doing COUNT(id) in Esqueleto and Yesod

esqueleto, haskell, persistent, yesod

Solution

Here's some old code I have that does a count, I don't remember much about this, but hopefully it helps!

selectCount
  :: (From SqlQuery SqlExpr SqlBackend a)
  => (a -> SqlQuery ()) -> Persist Int
selectCount q = do
  res <- select $ from $ (\x -> q x >> return countRows)
  return $ fromMaybe 0 $ (\(Value a) -> a) <$> headMay res

getCount :: RepositoryUri -> Persist Int
getCount ruri =
  selectCount $ \(r `InnerJoin` rs) -> do
    on     $ r ^. R.RepositoryId  ==. rs ^. Repo
    where_ $ r ^. R.Uri ==. val ruri

Problem

I'm trying to figure out how to write the following query using Esqueleto ``` SELECT COUNT("person"."id") FROM "person" WHERE (("person"."admin" = 't' OR "person"."vip" = 't') // 't' as in True OR "person"."karma" >= 5000 AND "person"."hellbanned" = 'f') ``` Here's how my model is defined ``` Person admin Bool vip Bool karma Int hellbanned Bool ``` I've managed to get almost everything, except for the `COUNT` part ``` select $ from $ \p -> do where_ ((p ^. PersonAdmin ==. val True) ||. (p ^. PersonVip ==. val True) &&. (p ^. PersonKarma >=. val 5000) &&. (p ^. PersonHellbanned ==. val False)) return $ p ^. PersonId ``` I managed to find a `countRows` function, however I haven't managed to find a way to combine these two in a way that typechecks. I'm also not sure if I need all those `p ^.` in each branch of the where clause, or if those can be collapsed together somehow?

Original source