nestedFilterOp :: forall record typ.
       ( PersistField typ
       , PersistEntityBackend record ~ DB.MongoContext
       ) => PersistFilter -> NestedField record typ -> typ -> Filter record
nestedFilterOp op nf v = BackendFilter $
   NestedFilter nf $ PersistFilterOperator (Left v) op
nestedFilterOp :: forall record typ.
       ( PersistField typ
       , PersistEntityBackend record ~ DB.MongoContext
       ) => PersistFilter -> NestedField record typ -> typ -> Filter record
nestedFilterOp op nf v = BackendFilter $
   NestedFilter nf $ PersistFilterOperator (Left v) op
nestedFilterOp op nf v = BackendFilter $
   NestedFilter nf $ PersistFilterOperator (Left v) op