The docs give this example of a policy:

policy action_type([:create, :update, :destroy]) do
  authorize_if expr(owner_id == ^actor(:id))
end

This is in the context of a policy group. Using it throws an error that filter expressions cannot be used for creations. I also get if I do it outside a group:

policy action_type(:create) do
  authorize_if expr(owner_id == ^actor(:id))
end

I read and understood the error message and it makes sense since there is no data yet for create, but how would you ensure that an actor can only create a resource for themselves?

I would like to do this:

MyApp.Items.create_item(%{
    title: "New item",
    user_id: user.id
  },
  actor: user
)

I’m also wondering more out of curiosity (even though I don’t want to do it this way) is there is a way to reference actor in action in change? For example, I tried to do this:

create :create do
  accept [:title]
  change set_attribute(:user_id, actor(:id))
end

though I see actor/1 is only available in expr (I think?)

Thanks!