Hello, I’m looking to dry up some LiveView handle_info/event callbacks that require modifying a nested data structure using update_in/3 in response to CRUD, or rather CUD, actions. The second parameter for update_in/3 is a list of keys that are often functions from the Access module e.g. Access.key!/2 and Access.filter/2.

For the sake of a concrete example, Person has many Pets, Pet has many Toys, and there are callbacks that update a preloaded person struct assigned to the socket after a user adds, updates, and/or deletes a toy. For the add and delete callbacks, update_in/3 only has to reach into the toys list whereas the update callback goes a step further to find the specific toy within in the toy list.

How would I go about abstracting out the common parts of the traverse path?

person =
  %Person{
    pets: [
      %Pet{
        toys: [
          %Toy{}
        ]
      }
    ]
  }

# within toy created callback
update_in(
  person,
  [
    Access.key!(:pets),
    Access.filter(&(&1.id == pet_id)),
    Access.key!(:toys)
  ],
  fn toys -> [toy | toys] end
) 

# within toy deleted callback
update_in(
  person,
  [
    Access.key!(:pets),
    Access.filter(&(&1.id == pet_id)),
    Access.key!(:toys)
  ],
  fn toys -> Enum.reject(toys, &(&1.id == toy_id)) end
) 

# within toy updated callback
update_in(
  person,
  [
    Access.key!(:pets),
    Access.filter(&(&1.id == pet_id)),
    Access.key!(:toys),
    Access.filter(&(&1.id == toy_id))
  ],
  fn toy -> %{toy | new_attributes} end
) 

# composing list of keys within toy updated callback
update_in(
  person,
  [
    Access.key!(:pets),
    Access.filter(&(&1.id == pet_id)),
    Access.key!(:toys)
  ] ++ [Access.filter(&(&1.id == toy_id))],
  fn toy -> %{toy | new_attributes} end
) 

As demonstrated above, the first three elements in the second parameter list of keys are shared across all three callbacks. Is there a sensible way to refactor and abstract that out? I imagine some form of macros/quote/unquote would be involved… would the added brevity even be worth it given the increased complexity?