How to approach editing in layered approach from "Designing Elixir Systems with OTP"?

Questions / Help
1

Throughout the book, the examples deal mostly with creating data. When the quiz runs, it always persists new answers.

Let’s say I want to add UI for creating quizzes, and it has ability to edit templates for the quiz. How would you design the core API for that function? I came up with something like this:

def edit_template(quiz, template, fields_to_update)

It is a little bit awkward to test, though. Because I need to get the template from a sequence of pipes like this:

quiz =
  Quiz.new
  |> Quiz.add_template(template_fields)

template = Quiz.get_template_by_name(name)

quiz =
  Quiz.edit_template(quiz, template, template_fields)

Is there a clearly better aproach? Or maybe dealing with mutable/nested data always will be a little awkward.

2

Pinging @JEG2 since you were very helpful with the last question :slight_smile:

3

My instinct is that we could add a new data structure for tracking quiz building. It might look something like this:

defmodule QuizBuilder do
  defstruct quiz: Quiz.new, templates: Map.new # …

  # functions here take and modify the struct above
end

Then I suspect edits will compose much better, with normal pipes.

4

@JEG2 I wonder what would you add as a key in that map. Let’s say I’ve added UUID to the template, and I generate one in Template.new:

def new(template_fields) do
  template_fields =
    template_fields
    |> Keyword.merge(uuid: UUID.generate())
  struct!(%__MODULE__{}, template_fields)
end

Then, if the map is %{uuid => template} it doesn’t help a lot. I still need to extract the template uuid.

Alternatively, I could try not generating UUID in the new function, then test builders would normally create the UUID as other fields, so the functions would be of shape.

def edit_template(quiz_builder, template_uuid, template_fields)
# previously, it was `template` struct instead of `temlate_uuid`

Now, there is another problem: where do I generate the UUID? I don’t think I want API user to pass the UUID every time when they create new template. Is it OK to generate the UUID in the API layer?

5

I was thinking you might store them by name, to skip step two of your example.

6

I was also thinking about storing them by name but then I can’t edit the name, so I thought some kind of permanent id (uuid) would work better.