I usually avoid making request to a database inside changesets. Instead, I use more explicit multis or transactions. So your second example I would write as:

  def changeset(record, attrs) do
    cast(record, attrs, [:issued_at, :due_for_return, :returned_at, :fee, :fee_paid_at])
  end

  defp valid_book_multi(multi, book_id) do
    alias Ecto.Multi
     
    Multi.run(multi, :book, fn _changes -> 
       case Book.get(book_id) do
          %Book{status: :available} = available_book -> {:ok, available_book}
          %Book{status: status} = not_available_book -> {:error, Book.error_msg(:status, status)}
          nil -> {:error, :not_found}
       end
    end)
  end

  @spec create_record(%{(String.t | atom) => term}, book_id: pos_integer) :: {:ok, %Record{}} | {:error, Ecto.Changeset.t}
  def create_record(attrs, book_id: book_id) do
    alias Ecto.Multi

   record_changeset = changeset(%Record{book_id: book_id}, attrs)

    Multi.new()
    |> valid_book_multi(book_id)
    |> Multi.insert(:record, record_changeset)
    |> Repo.transaction()
    |> case do
      {:ok, %{record: record}} -> {:ok, record}
      {:error, :book, reason, _changes} -> # collect errors into record changesets
    end
  end

Changeset validation functions should be limited to pure functions that use the data available to them in the Changeset and arguments you pass. They are not “models”. Business rules that require data access, messaging etc should be implemented in another module - if you are using Phoenix it would be a context module - but regardless its just a module with functions.

What about using Ecto.Changeset.prepare_changes ?

Provides a function to run before emitting changes to the repository.

Such function receives the changeset and must return a changeset, allowing developers to do final adjustments to the changeset or to issue data consistency commands.

The given function is guaranteed to run inside the same transaction as the changeset operation for databases that do support transactions.

I will run some validation and returns an invalid changeset if it failed.