update_in/3 and friends are plain functions, and their argument is a plain list (of anonymous functions). The macro-sorcery might be necessary to do things with update_in/2, but not here.
You could do this with functions:
defp toys_for(pet_id) do
[
Access.key!(:pets),
Access.filter(&(&1.id == pet_id)),
Access.key!(:toys)
]
end
# in the created/deleted callbacks:
update_in(
person,
toys_for(pet_id),
fn toys -> [toy | toys] end
)
# in the updated callback:
update_in(
person,
toys_for(pet_id) ++ [Access.filter(&(&1.id == toy_id))],
fn toy -> %{toy | new_attributes} end
)
You could also split this differently - combine Access.key!(:pets) with the Access.filter and name it pet_with_id or similar.
