Rawmongo

You will need to use the raw driver with Persistent to deal with embedded fields. Note also that toInsertFields and entityToFields are available to help with embedded documents.

import Database.MongoDB((=:))
import Database.MongoDB (Document, Action, findOne)
import qualified Database.MongoDB as MongoDB

rawOne :: Trans.MonadIO m => MongoDB.Collection -> MongoDB.Selector -> Action m (Maybe Document)
rawOne collection q = findOne (MongoDB.select q collection)

theCollection :: Trans.MonadIO m
theCollection = rawOne $ "collection-name"

getTheR theId = do
  Just doc <- runDB $ theCollection ["_id" =: theId]