What do you do when you have a Thing but no db id?

Thing.hs

#!/usr/bin/env stack
-- stack script --resolver lts-8.12
{-# LANGUAGE OverloadedStrings #-}

import Data.Text
import System.Random

data Thing = Thing { id :: Int, name :: Text } deriving Show

main :: IO ()
main = do
  let thing1 = flip Thing "Pauly Shore"
  let thing2 = flip Thing "Terry Kiser"

  print =<< save thing1
  print =<< save thing2

  let thing1' = Thing' "Jason Silverman"
  let thing2' = Thing' "Jason Bateman"

  print =<< save' thing1'
  print =<< save' thing2'

{-
 Since all things in Haskell are functions (big stretch here), we can represent our Thing without
 an id as a partially applied function.  Not useful, but including it to illustrate the problem.

 Type aliases can be useful in this context because we can give our partially applied function
 a type. Unfortunately this limits access to the data inside the UnsavedThing, making this approach
 problematic for anything practical (like saving that data in the db).
-}

type UnsavedThing = (Int -> Thing)

save :: UnsavedThing -> IO Thing
save unsavedThing = do
  id' <- saveOperation unsavedThing
  pure $ unsavedThing id'
        -- Problem: How can I extract the data to save from a partially applied function?
  where saveOperation unsavedThing = randomIO

{-
 To work around this, you could construct pairs of ids and Things and use a convenience Type alias.
 This is a zero abstraction approximation of what Persistent is doing but without the overhead of TemplateHaskell.
-}

data Thing' = Thing' { name' :: Text } deriving Show

type IdThing' = (Int, Thing')

save' :: Thing' -> IO IdThing'
save' thing = do
  id' <- saveOperation thing
  pure (id', thing)
  where saveOperation thing = const randomIO thing