Use Cases and building Phoenix applications around them

Using Use Cases in modelling your phoenix application and contexts.

Transcript

1. Use Cases …and building Phoenix applications around them
2. What is a Use Case?
3. https://www.usability.gov/how-to-and-tools/methods/use-cases.html “A use case is a written description of how users will perform tasks on your website. It outlines, from a user’s point of view, a system’s behaviour as it responds to a request. Each use case is represented as a sequence of simple steps, beginning with a user's goal and ending when that goal is fulfilled.”
4. Laundry Basic Flow Example Use Case
5. Actor Laundryman
6. Input data
 (Laundry items) Sort laundry Wash laundry
7. Dry laundry Fold all laundry items Output data
 (Finished laundry items)
8. Phoenix contexts From Use Case to code
9. defmodule Chores.Laundry do def create_laundry do . . . end def update_laundry do . . . end . . . end defmodule Chores.Laundryman do # laundryman user specific logic end
10. Classic approach • Context for Laundryman • basic User stuff • Context for Laundry: • create, update and delete • Additional functions to handle our 
 Use Case create_* update_* delete_* sort_* wash_* dry_* fold_*
13. So why even implement them as a public method? Most of the functions are generic
14. Modules can have names based on something else than nouns :) Use verbs
15. defmodule Chores.Laundry.DoLaundry do # scrap logic from Phoenix generators end defmodule Chores.Laundry do # delegates to use cases modules (optional) end defmodule Chores.Laundryman do # laundryman user specific logic end
17. defmodule Chores.Laundry.DoLaundry do def call(args) do # handle the use case with private functions end defp sort(args) do . . . end defp wash(args) do . . . end defp dry(args) do . . . end defp fold(args) do . . . end end
18. defmodule Chores.Laundry.DoLaundry do def call(input_data) do with {:ok, laundry} <- sort(input_data), {:ok, laundry} <- wash(laundry), {:ok, laundry} <- dry(laundry), {:ok, laundry} <- fold(laundry) do {:ok, laundry} end . . . end
19. Structs are really cool :) Define clear interface
20. defmodule Chores.Laundry.DoLaundry do defmodule Data do @type t :: %__MODULE__{ laundryman_id: String.t(), laundry_items: list } @enforce_keys [:laundryman_id, :laundry_items] defstruct [:laundryman_id, :laundry_items] def new(params) do %Data{ laundryman_id: params[:laundryman_id], laundry_items: params[:laundry_items] } end end . . . end
21. casting params to Data struct… Now use it
22. defmodule Chores.Laundry.DoLaundry do . . . def call(params) do data = Data.new(params) pipeline(data) end defp pipeline(data) do with {:ok, laundry} <- sort(data), {:ok, laundry} <- wash(laundry), {:ok, laundry} <- dry(laundry), {:ok, laundry} <- fold(laundry) do {:ok, laundry} end . . . end
23. Ecto.Multi && Repo.transaction Transactions?
24. So why it’s good? The key benefits of writing code based on behaviour
25. Explicit requirements
26. defmodule Chores.Laundry.DoLaundry do defmodule Data do @type t :: %__MODULE__{ laundryman_id: String.t(), laundry_items: list } @enforce_keys [:laundryman_id, :laundry_items] defstruct [:laundryman_id, :laundry_items] def new(params) do %Data{ laundryman_id: params[:laundryman_id], laundry_items: params[:laundry_items] } end end . . . end
27. defmodule Chores.Laundry.DoLaundry do defmodule Data do @type t :: %__MODULE__{ laundryman_id: String.t(), laundry_items: list } @enforce_keys [:laundryman_id, :laundry_items] defstruct [:laundryman_id, :laundry_items] def new(params) do %Data{ laundryman_id: params[:laundryman_id], laundry_items: params[:laundry_items] } end end . . . end
28. Limited coupling
29. Code organisation and clarity
30. defmodule Chores.Laundry.DoLaundry do . . . def call(params) do data = Data.new(params) pipeline(data) end defp pipeline(laundry) do with {:ok, laundry} <- sort(laundry), {:ok, laundry} <- wash(laundry), {:ok, laundry} <- dry(laundry), {:ok, laundry} <- fold(laundry) do {:ok, laundry} end . . . end
31. defmodule Chores.Laundry.DoLaundry do . . . def call(params) do data = Data.new(params) pipeline(data) end defp pipeline(laundry) do with {:ok, laundry} <- sort(laundry), {:ok, laundry} <- wash(laundry), {:ok, laundry} <- dry(laundry), {:ok, laundry} <- fold(laundry) do {:ok, laundry} end . . . end
32. Easy to modify
33. Dry laundry Fold all laundry items Output data
 (Finished laundry items) Some more processing
34. defmodule Chores.Laundry.DoLaundry do . . . def call(params) do data = Data.new(params) pipeline(data) end defp pipeline(laundry) do with {:ok, laundry} <- sort(laundry), {:ok, laundry} <- wash(laundry), {:ok, laundry} <- dry(laundry), {:ok, laundry} <- some_more_processing(laundry), {:ok, laundry} <- fold(laundry) do {:ok, laundry} end . . . end
35. defmodule Chores.Laundry.DoLaundry do . . . def call(params) do data = Data.new(params) pipeline(data) end defp pipeline(laundry) do with {:ok, laundry} <- sort(laundry), {:ok, laundry} <- wash(laundry), {:ok, laundry} <- dry(laundry), {:ok, laundry} <- some_more_processing(laundry), {:ok, laundry} <- fold(laundry) do {:ok, laundry} end . . . end
36. Pitfalls
37. Too big features
38. defmodule Client.Create.HotelReservation do require XXX use XXX.Pipeline defcall [:conn, :params] defmodule Data do @type t :: %__MODULE__{ # enforced booking: XXX.HotelBooking.t(), previous_message_id: String.t(), user: %XXX.User{}, # optional agent: %XXX.Agent{} | nil, card: %XXX.Card{} | nil, companions: [%XXX.Companion{}] | nil, confirmation_message: %XXX.Message{} | nil, confirmation_message_body: XXX.BodyType.t() | nil, decoded_previous_message: XXX.BodyType.t() | nil, previous_message: %XXX.Message{} | nil, request: map | nil, response: map | nil, text_message: %XXX.Message{} | nil, text_message_body: XXX.BodyType.t() | nil, . . .
39. defmodule Client.Create.HotelReservation do require XXX use XXX.Pipeline defcall [:conn, :params] defmodule Data do @type t :: %__MODULE__{ # enforced booking: XXX.HotelBooking.t(), previous_message_id: String.t(), user: %XXX.User{}, # optional agent: %XXX.Agent{} | nil, card: %XXX.Card{} | nil, companions: [%XXX.Companion{}] | nil, confirmation_message: %XXX.Message{} | nil, confirmation_message_body: XXX.BodyType.t() | nil, decoded_previous_message: XXX.BodyType.t() | nil, previous_message: %XXX.Message{} | nil, request: map | nil, response: map | nil, text_message: %XXX.Message{} | nil, text_message_body: XXX.BodyType.t() | nil, . . .
41. Testing
42. defmodule Client.Create.HotelReservation do require XXX use XXX.Pipeline defcall [:conn, :params] defmodule Data do @type t :: %__MODULE__{ # enforced booking: XXX.HotelBooking.t(), previous_message_id: String.t(), user: %XXX.User{}, # optional agent: %XXX.Agent{} | nil, card: %XXX.Card{} | nil, companions: [%XXX.Companion{}] | nil, confirmation_message: %XXX.Message{} | nil, confirmation_message_body: XXX.BodyType.t() | nil, decoded_previous_message: XXX.BodyType.t() | nil, previous_message: %XXX.Message{} | nil, request: map | nil, response: map | nil, text_message: %XXX.Message{} | nil, text_message_body: XXX.BodyType.t() | nil, . . .
43. defmodule Chores.Laundry.DoLaundry do . . . def call(params) do data = Data.new(params) pipeline(data) end defp pipeline(laundry) do with {:ok, laundry} <- sort(laundry), {:ok, laundry} <- wash(laundry), {:ok, laundry} <- dry(laundry), {:ok, laundry} <- some_more_processing(laundry), {:ok, laundry} <- fold(laundry) do {:ok, laundry} end . . . end
44. Conclusions
45. Sources and inspirations https://luizdamim.com/blog/reorganizing-your-phoenix-contexts-as-use-cases https://www.usability.gov/how-to-and-tools/methods/use-cases.html Icons: www.flaticon.com Contact j.pieta96@gmail.com Github: @jakubpieta