So here is the code I came up with to generically generate an array param that will be stored on a jsonb property in ecto.

It only handles the root level, and is pretty limited, but I’m curious if the community has a better/more elegant/easier solution than I do. Let me re-phrase, I really believe you do, I just wanted to solicit advice.

Problem: jsonb array of objects stored on an Ecto model, these objects can be updated or added.

  @doc "if the id is in the map already, update it, otherwise append it"
  defp upsert_embed(%{id: id} = params, collection) when is_list(collection) do
   case Enum.find(collection, &(&1.id == id)) do
     nil -> collection ++ [params]
     found -> updated = Map.merge(found, params)
              collection = collection -- [found] ## This is the piece I'm really not confident in.
              collection = collection ++ [updated]
   end
  end
  @doc "provided map doesn't have an id"
  defp upsert_embed(%{} = params, collection) when is_list(collection) do
    collection ++ [params]
  end

  @doc """
  adds or updates a child object of an array of maps.
  """
  def upsert_embedded_field(%__struct__{} = struct, key, %{} = candidate_params) do
    updated_embeds = Map.get(struct, key) || []
    updated_embeds = case length(updated_embeds) do
       0 ->
          upsert_embed(candidate_params, updated_embeds)
       _ ->
          updated_embeds = Enum.reduce(updated_embeds, updated_embeds,  fn(e, collection) ->
            upsert_embed(candidate_params, collection)
          end)
       end
     # Return the mutated list
      updated_embeds
  end