Documentation

A polymorphic version of patchValue

The patch input uses AsValue from aeson-optics, meaning you can supply a variety of types such as ByteString or Value and it will be parsed into [Patches] (capturing failure as a PatchError).

The v input can be any domain type with JSON instances. We don't use AsValue here as well, even though it provides the same functionality, because it's unlikely your types will have this instance.

data Person = Person
  { name :: Text
  , age :: Int
  }
  deriving stock Generic
  deriving anyclass (FromJSON, ToJSON)

patchPersonR :: PersonId -> Handler Person
patchPersonR id = do
  person <- runDB $ get id           -- Person "pat" 19
  bytes <- getRequestBody            -- "[{op:replace, path:/age, value:21}]"

  case patchAsValue bytes person of
    Left err -> sendResponse 400 $ displayException err
    Right updated -> do
      runDB $ update id updated
      sendResponse 200 updated       -- Person "pat" 21

If the patch creates a value that can't parse back to your domain type, that will also be normalized to PatchError.