Implementing jsonb_build_object

[remeike]

So I've been struggling to implement postgresql's jsonb_build_object via Rel8's function. (I'm trying to construct a JSON object inside a query so if there's another way to do this that I'm missing, do let me know.)

The issue is that that the arguments to jsonb_build_object are in fact variadic. Now I can do something like the following...

jsonbBuildObject2 :: (Expr Text, Expr Value) -> (Expr Text, Expr Value) -> Expr Value 
jsonbBuildObject2 (k1, v1) (k2, v2) = 
  function "jsonb_build_object" (k1, v1, k2, v2)

And that will work. But let's say I want to build an object with more fields like this:

jsonbBuildObject4 ::
  (Expr Text, Expr Value) ->
  (Expr Text, Expr Value) ->
  (Expr Text, Expr Value) ->
  (Expr Text, Expr Value) ->
  Expr Value
jsonbBuildObject4 (k1, v1) (k2, v2) (k3, v3) (k4, v4) =
  function "jsonb_build_object" (k1, v1, k2, v2, k3, v3, k4, v4)

And now that won't compile because I've got a tuple that's too big. And even if it worked it's still a tedious way to build objects. Ideally I would like to create a function that looks like the following:

jsonbBuildObject :: [(Expr Text, Expr Value)] -> Expr Value 
jsonbBuildObject fields =
  ...

But I just can't figure out how to make this work with the functions currently exported by the library.

[remeike]

Something like this would probably work:

import qualified Opaleye.Internal.HaskellDB.PrimQuery as Opaleye

jsonbBuildObject :: [(Expr Text, Expr Value)] -> Expr Value
jsonbBuildObject fields =
  unsafePrimExpr
    $ Opaleye.FunExpr "jsonb_build_object"
    $ foldMap (\(k,v) -> [toPrimExpr k, toPrimExpr v]) fields

So with the latest version of Rel8 I'm halfway there now that it exports unsafePrimExpr, but I'd still need an unsafe function that converts Rel8's Expr a to Opaleye's PrimExpr and I don't think any such function is currently exported by the library.