Absinthe: resolving joins

I’m working to set up my first GraphQL API and I got stuck on how to properly join between 2 related models. In the classic example, one user has many posts. This tutorial showed how to join from a post to a user, but I can’t figure it out the other way around… I don’t see an example of this in the Absinthe book either.

My resolver module looks something like this:

defmodule ApiWeb.Schema.MySchema do
  use Absinthe.Schema.Notation

  use Absinthe.Ecto, repo: Api.Repo

  object :parent_thing do
    @desc "UUID unique identifier"
    field(:id, :string)
    @desc "Name of the thing"
    field(:name, :string)
    @desc "Children"
    # This returns results, but with nil values
    field(:children, list_of(:child_thing))
    # This doesn't work at all
    field(:children, list_of(:child_thing), resolve: assoc(:uploads))
    # This works, but it does not filter the children by the parent
    field(:children, list_of(:child_thing), resolve: &Api.Children.get_list/3)
  end

  object :child_thing do
    @desc "UUID unique identifier"
    field(:id, :string)
    field(:parent_id, :string)
    field(:name, :string)
  end
end

Can anyone help shed some light on this? Thanks!