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Making Invalid States Invalid in LiveView

German Velasco
October 15, 2021
Technology
690
1

Making Invalid States Invalid in LiveView

Have you ever found a bug in your LiveView code because your app somehow had invalid and incoherent state?

“Your total is -$500.”
“Your return flight is .”
“The temperature is -600°F.”

When programming user interfaces, it’s important that we do not display inconsistent states to our users. But how can we prevent those bugs?

By making those invalid states impossible to represent!

Join me as we walk through a LiveView example that has bugs because of invalid states. As we fix them, you’ll learn to model domains in a way that makes rendering invalid states impossible. Your users and your future self will thank you.

German Velasco

October 15, 2021

Transcript

196 slides

  1. MAKING INVALID STATES INVALID in LiveView

  2. MAKING INVALID STATES INVALID in LiveView AN EXPLORATION

  3. WHAT DOES THAT MEAN?

  4. How we model our domain constrains what states are allowed

  5. Model our domain to remove states we don't want

  6. NOT NEW

  7. NOT NEW ▸ OCaml

  8. NOT NEW ▸ OCaml ▸ Elm

  9. NOT NEW ▸ OCaml ▸ Elm ▸ F#

  10. OTHER NAMES

  11. OTHER NAMES ▸ Making invalid states unrepresentable

  12. OTHER NAMES ▸ Making invalid states unrepresentable ▸ Making illegal

    states unrepresentable

  13. OTHER NAMES ▸ Making invalid states unrepresentable ▸ Making illegal

    states unrepresentable ▸ Making impossible states impossible

  14. BRINGING IT TO LiveView

  15. BRINGING IT TO LiveView ▸ Persistent state

  16. BRINGING IT TO LiveView ▸ Persistent state ▸ That our

    users see

  17. A FLIGHT BOOKER EXAMPLE !

  18. None

  19. FIRST IMPLEMENTATION

  20. ASSIGNING VALUES def mount(_, _, socket) do { :ok, socket

    |> assign(:direction, "one-way") |> assign(:departure, Date.utc_today()) |> assign(:return, nil) } end

  21. ASSIGNING VALUES def mount(_, _, socket) do { :ok, socket

    |> assign(:direction, "one-way") |> assign(:departure, Date.utc_today()) |> assign(:return, nil) } end

  22. RENDERING THE ASSIGNS <form phx-submit="book"> <%= select :booking, :flight_type, ["one-way",

    "two-way"], value: @direction %> <%= text_input :booking, :departure, value: @departure %> <%= text_input :booking, :return, value: @return %> <%= submit "Book" %> </form>

  23. RENDERING THE ASSIGNS <form phx-submit="book"> <%= select :booking, :flight_type, ["one-way",

    "two-way"], value: @direction %> <%= text_input :booking, :departure, value: @departure %> <%= text_input :booking, :return, value: @return %> <%= submit "Book" %> </form>

  24. RENDERING THE ASSIGNS <form phx-submit="book"> <%= select :booking, :flight_type, ["one-way",

    "two-way"], value: @direction %> <%= text_input :booking, :departure, value: @departure %> <%= text_input :booking, :return, value: @return %> <%= submit "Book" %> </form>

  25. RENDERING THE ASSIGNS <form phx-submit="book"> <%= select :booking, :flight_type, ["one-way",

    "two-way"], value: @direction %> <%= text_input :booking, :departure, value: @departure %> <%= text_input :booking, :return, value: @return %> <%= submit "Book" %> </form>

  26. HANDLING THE EVENT def handle_event("book", %{"booking" => params}, socket) do

    {:ok, message} = FlightBooker.book_trip(params) socket |> put_flash(:info, message) |> noreply() end

  27. HANDLING THE EVENT def handle_event("book", %{"booking" => params}, socket) do

    {:ok, message} = FlightBooker.book_trip(params) socket |> put_flash(:info, message) |> noreply() end

  28. BOOKING THE TRIP def book_trip(params) do case params do %{"flight_type"

    => "one-way", "departure" => departure} -> {:ok, one_way_message(departure)} %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> {:ok, two_way_message(departure, return)} end end

  29. BOOKING THE TRIP def book_trip(params) do case params do %{"flight_type"

    => "one-way", "departure" => departure} -> {:ok, one_way_message(departure)} %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> {:ok, two_way_message(departure, return)} end end

  30. BOOKING THE TRIP def book_trip(params) do case params do %{"flight_type"

    => "one-way", "departure" => departure} -> {:ok, one_way_message(departure)} %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> {:ok, two_way_message(departure, return)} end end
  31. None

  32. ! THE BUGS

  33. ! THE BUGS

  34. ! THE BUGS ▸ ! One-way flight that got charged

    for a return flight

  35. ! THE BUGS ▸ ! One-way flight that got charged

    for a return flight ▸ " Two-way flight without a return flight

  36. OUR CURRENT (IMPLICIT) DOMAIN MODEL %{ direction: "one-way" | "two-way",

    departure: Date.t() | nil, return: Date.t() | nil }

  37. OUR CURRENT (IMPLICIT) DOMAIN MODEL %{ direction: "one-way" | "two-way",

    departure: Date.t() | nil, return: Date.t() | nil }

  38. OUR CURRENT (IMPLICIT) DOMAIN MODEL %{ direction: "one-way" | "two-way",

    departure: Date.t() | nil, return: Date.t() | nil }

  39. OUR CURRENT (IMPLICIT) DOMAIN MODEL %{ direction: "one-way" | "two-way",

    departure: Date.t() | nil, return: Date.t() | nil }

  40. OUR CURRENT (IMPLICIT) DOMAIN MODEL %{ direction: "one-way" | "two-way",

    departure: Date.t() | nil, return: Date.t() | nil }

  41. POSSIBLE STATES # one-way %{direction: "one-way", departure: Date.t(), return: Date.t()}

    %{direction: "one-way", departure: nil, return: Date.t()} %{direction: "one-way", departure: Date.t(), return: nil} %{direction: "one-way", departure: nil, return: nil} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t()} %{direction: "two-way", departure: nil, return: Date.t()} %{direction: "two-way", departure: Date.t(), return: nil} %{direction: "two-way", departure: nil, return: nil}

  42. POSSIBLE STATES # one-way %{direction: "one-way", departure: Date.t(), return: Date.t()}

    %{direction: "one-way", departure: nil, return: Date.t()} %{direction: "one-way", departure: Date.t(), return: nil} %{direction: "one-way", departure: nil, return: nil} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t()} %{direction: "two-way", departure: nil, return: Date.t()} %{direction: "two-way", departure: Date.t(), return: nil} %{direction: "two-way", departure: nil, return: nil}

  43. POSSIBLE STATES # one-way %{direction: "one-way", departure: Date.t(), return: Date.t()}

    %{direction: "one-way", departure: nil, return: Date.t()} %{direction: "one-way", departure: Date.t(), return: nil} %{direction: "one-way", departure: nil, return: nil} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t()} %{direction: "two-way", departure: nil, return: Date.t()} %{direction: "two-way", departure: Date.t(), return: nil} %{direction: "two-way", departure: nil, return: nil}

  44. INVALID STATES # one-way %{direction: "one-way", departure: Date.t(), return: Date.t()}

    %{direction: "one-way", departure: nil, return: Date.t()} %{direction: "one-way", departure: Date.t(), return: nil} %{direction: "one-way", departure: nil, return: nil} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t()} %{direction: "two-way", departure: nil, return: Date.t()} %{direction: "two-way", departure: Date.t(), return: nil} %{direction: "two-way", departure: nil, return: nil}

  45. VALID STATES # one-way %{direction: "one-way", departure: Date.t(), return: Date.t()}

    %{direction: "one-way", departure: nil, return: Date.t()} %{direction: "one-way", departure: Date.t(), return: nil} %{direction: "one-way", departure: nil, return: nil} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t()} %{direction: "two-way", departure: nil, return: Date.t()} %{direction: "two-way", departure: Date.t(), return: nil} %{direction: "two-way", departure: nil, return: nil}

  46. ONLY 2/8 STATES ARE VALID! # one-way %{direction: "one-way", departure:

    Date.t(), return: nil} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t()}

  47. A MORE constrained FLIGHT BOOKER DOMAIN MODEL

  48. A MORE constrained FLIGHT BOOKER DOMAIN MODEL

  49. A MORE constrained FLIGHT BOOKER DOMAIN MODEL ▸ One-way flight

    with departure date

  50. A MORE constrained FLIGHT BOOKER DOMAIN MODEL ▸ One-way flight

    with departure date ▸ OR

  51. A MORE constrained FLIGHT BOOKER DOMAIN MODEL ▸ One-way flight

    with departure date ▸ OR ▸ Two-way flight with departure and return dates

  52. A MORE constrained FLIGHT BOOKER DOMAIN MODEL @type flight_booker ::

    {:one_way, Date.t()} | {:two_way, Date.t(), Date.t()}

  53. A MORE constrained FLIGHT BOOKER DOMAIN MODEL @type flight_booker ::

    {:one_way, Date.t()} | {:two_way, Date.t(), Date.t()}

  54. A MORE constrained FLIGHT BOOKER DOMAIN MODEL @type flight_booker ::

    {:one_way, Date.t()} | {:two_way, Date.t(), Date.t()}

  55. TAGGED VALUES defmodule FlightBooker do def one_way(%Date{} = date) do

    {:one_way, date} end def two_way(%Date{} = departure, %Date{} = return) do {:two_way, departure, return} end end

  56. TAGGED VALUES defmodule FlightBooker do def one_way(%Date{} = date) do

    {:one_way, date} end def two_way(%Date{} = departure, %Date{} = return) do {:two_way, departure, return} end end

  57. TAGGED VALUES defmodule FlightBooker do def one_way(%Date{} = date) do

    {:one_way, date} end def two_way(%Date{} = departure, %Date{} = return) do {:two_way, departure, return} end end

  58. TAGGED VALUES defmodule FlightBooker do def one_way(%Date{} = date) do

    %OneWay{departure: date} end def two_way(%Date{} = departure, %Date{} = return) do %TwoWay{departure: departure, return: return} end end

  59. TAGGED VALUES defmodule FlightBooker do def one_way(%Date{} = date) do

    %OneWay{departure: date} end def two_way(%Date{} = departure, %Date{} = return) do %TwoWay{departure: departure, return: return} end end

  60. TAGGED VALUES defmodule FlightBooker do def one_way(%Date{} = date) do

    {:one_way, date} end def two_way(%Date{} = departure, %Date{} = return) do {:two_way, departure, return} end end

  61. IMPLICATIONS OF OUR NEW DOMAIN MODEL

  62. IMPLICATIONS OF OUR NEW DOMAIN MODEL ▸ Render complex types

  63. IMPLICATIONS OF OUR NEW DOMAIN MODEL ▸ Render complex types

    ▸ Handle events with user input

  64. 1. RENDER COMPLEX TYPE def mount(_, _, socket) do today

    = Date.utc_today() booker = FlightBooker.one_way(today) {:ok, assign(socket, :booker, booker)} end

  65. 1. RENDER COMPLEX TYPE def mount(_, _, socket) do today

    = Date.utc_today() booker = FlightBooker.one_way(today) {:ok, assign(socket, :booker, booker)} end

  66. 1. RENDER COMPLEX TYPE <form phx-submit="book" phx-change="update"> <%= case @booker

    do %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, disabled: true %> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, value: return %> <% end %> <%= submit "Book" %> </form>

  67. 1. RENDER COMPLEX TYPE <form phx-submit="book" phx-change="update"> <%= case @booker

    do %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, disabled: true %> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, value: return %> <% end %> <%= submit "Book" %> </form>

  68. 1. RENDER COMPLEX TYPE <form phx-submit="book" phx-change="update"> <%= case @booker

    do %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, disabled: true %> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, value: return %> <% end %> <%= submit "Book" %> </form>

  69. 1. RENDER COMPLEX TYPE <form phx-submit="book" phx-change="update"> <%= case @booker

    do %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, disabled: true %> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, value: return %> <% end %> <%= submit "Book" %> </form>

  70. 1. RENDER COMPLEX TYPE <form phx-submit="book" phx-change="update"> <%= case @booker

    do %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, disabled: true %> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, value: return %> <% end %> <%= submit "Book" %> </form>

  71. FORCED TO HANDLE RETURN ON "ONE-WAY" FLIGHT <form phx-submit="book" phx-change="update">

    <%= case @booker do %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, disabled: true %> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, value: return %> <% end %> <%= submit "Book" %> </form>

  72. FORCED TO HANDLE RETURN ON "ONE-WAY" FLIGHT <form phx-submit="book" phx-change="update">

    <%= case @booker do %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, disabled: true %> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, value: return %> <% end %> <%= submit "Book" %> </form>

  73. FORCED TO HANDLE RETURN ON "ONE-WAY" FLIGHT <form phx-submit="book" phx-change="update">

    <%= case @booker do %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <%= text_input :booking, :departure, value: departure %> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <%= text_input :booking, :departure, value: departure %> <%= text_input :booking, :return, value: return %> <% end %> <%= submit "Book" %> </form>

  74. INVALID STATE REMOVED %{ direction: "one-way", departure: Date.t(), return: Date.t()

    }

  75. 2. HANDLE EVENTS

  76. TRANSFORM USER INPUT THROUGH PARSING

  77. TRANSFORM USER INPUT THROUGH PARSING ▸ less structured data |>

    more structured data

  78. TRANSFORM USER INPUT THROUGH PARSING ▸ less structured data |>

    more structured data ▸ raw data |> valid domain

  79. TRANSFORM USER INPUT THROUGH PARSING ▸ less structured data |>

    more structured data ▸ raw data |> valid domain ▸ ⚠ |>

  80. HANDLE EVENT def handle_event("book", %{"booking" => params}, socket) do {:ok,

    message} = params |> parse_params_into_booking() |> FlightBooker.book_trip() socket |> put_flash(:info, message) |> noreply() end

  81. HANDLE EVENT def handle_event("book", %{"booking" => params}, socket) do {:ok,

    message} = params |> parse_params_into_booking() |> FlightBooker.book_trip() socket |> put_flash(:info, message) |> noreply() end

  82. HANDLE EVENT def handle_event("book", %{"booking" => params}, socket) do {:ok,

    message} = params |> parse_params_into_booking() |> FlightBooker.book_trip() socket |> put_flash(:info, message) |> noreply() end

  83. defp parse_params_into_booking(params) do case params do %{"flight_type" => "one-way", "departure"

    => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  84. defp parse_params_into_booking(params) do case params do %{"flight_type" => "one-way", "departure"

    => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  85. defp parse_params_into_booking(params) do case params do %{"flight_type" => "one-way", "departure"

    => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  86. defp parse_params_into_booking(params) do case params do %{"flight_type" => "one-way", "departure"

    => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  87. defp parse_params_into_booking(params) do case params do %{"flight_type" => "one-way", "departure"

    => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  88. defp parse_params_into_booking(params) do case params do %{"flight_type" => "one-way", "departure"

    => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  89. defp parse_params_into_booking(params) do case params do %{"flight_type" => "one-way", "departure"

    => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  90. INVALID STATE REMOVED %{ direction: "two-way", departure: Date.t(), return: nil

    }

  91. defp parse_params_into_booking(params) do case params do %{"flight_type" => "one-way", "departure"

    => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  92. INVALID STATES REMOVED %{direction: "one-way", departure: nil, return: nil} %{direction:

    "one-way", departure: nil, return: Date.t()} %{direction: "two-way", departure: nil, return: nil} %{direction: "two-way", departure: nil, return: Date.t()}

  93. Without any error handling, we have removed 6 invalid states!

  94. WHAT ABOUT ERROR HANDLING?

  95. WHAT ABOUT ERROR HANDLING? ▸ Validate and present errors

  96. WHAT ABOUT ERROR HANDLING? ▸ Validate and present errors ▸

    Potential for same problems

  97. POSSIBLE ERRORS @type error_fields :: :departure | :return @type errors

    :: [error_fields]

  98. ADDING ERRORS ASSIGN socket |> assign(:direction, "one-way") |> assign(:departure, Date.utc_today())

    |> assign(:return, nil) + |> assign(:errors, [])

  99. (PREVIOUS) POSSIBLE STATES # one-way %{direction: "one-way", departure: Date.t(), return:

    Date.t()} %{direction: "one-way", departure: nil, return: Date.t()} %{direction: "one-way", departure: Date.t(), return: nil} %{direction: "one-way", departure: nil, return: nil} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t()} %{direction: "two-way", departure: nil, return: Date.t()} %{direction: "two-way", departure: Date.t(), return: nil} %{direction: "two-way", departure: nil, return: nil}

  100. (PREVIOUS) POSSIBLE STATES # one-way %{direction: "one-way", departure: Date.t(), return:

    Date.t()} %{direction: "one-way", departure: nil, return: Date.t()} %{direction: "one-way", departure: Date.t(), return: nil} %{direction: "one-way", departure: nil, return: nil} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t()} %{direction: "two-way", departure: nil, return: Date.t()} %{direction: "two-way", departure: Date.t(), return: nil} %{direction: "two-way", departure: nil, return: nil}

  101. # one-way %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: []}

    %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: [:departure]} %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: [:return]} %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: [:departure, :return]} %{direction: "one-way", departure: nil, return: Date.t()} %{direction: "one-way", departure: Date.t(), return: nil} %{direction: "one-way", departure: nil, return: nil} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t()} %{direction: "two-way", departure: nil, return: Date.t()} %{direction: "two-way", departure: Date.t(), return: nil} %{direction: "two-way", departure: nil, return: nil}

  102. 8 X 4 = 32 POSSIBLE STATES! # one-way %{direction:

    "one-way", departure: Date.t(), return: Date.t(), errors: []} %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: [:departure]} %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: [:return]} %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: [:departure, :return]} %{direction: "one-way", departure: nil, return: Date.t(), errors: []} %{direction: "one-way", departure: nil, return: Date.t(), errors: [:departure]} %{direction: "one-way", departure: nil, return: Date.t(), errors: [:return]} %{direction: "one-way", departure: nil, return: Date.t(), errors: [:departure, :return]} %{direction: "one-way", departure: Date.t(), return: nil, errors: []} %{direction: "one-way", departure: Date.t(), return: nil, errors: [:departure]} %{direction: "one-way", departure: Date.t(), return: nil, errors: [:return]} %{direction: "one-way", departure: Date.t(), return: nil, errors: [:departure, :return]} %{direction: "one-way", departure: nil, return: nil, errors: []} %{direction: "one-way", departure: nil, return: nil, errors: [:departure]} %{direction: "one-way", departure: nil, return: nil, errors: [:return]} %{direction: "one-way", departure: nil, return: nil, errors: [:departure, :return]} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: []} %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: [:departure]} %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: [:return]} %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: [:departure, :return]} %{direction: "two-way", departure: nil, return: Date.t(), errors: []} %{direction: "two-way", departure: nil, return: Date.t(), errors: [:departure]} %{direction: "two-way", departure: nil, return: Date.t(), errors: [:return]} %{direction: "two-way", departure: nil, return: Date.t(), errors: [:departure, :return]} %{direction: "two-way", departure: Date.t(), return: nil, errors: []} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:departure]} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:return]} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:departure, :return]} %{direction: "two-way", departure: nil, return: nil, errors: []} %{direction: "two-way", departure: nil, return: nil, errors: [:departure]} %{direction: "two-way", departure: nil, return: nil, errors: [:return]} %{direction: "two-way", departure: nil, return: nil, errors: [:departure, :return]}

  103. "Please select a valid return date" %{ direction: "one-way", departure:

    Date.t(), return: nil, errors: [:return] }

  104. "Please select a valid return date" %{ direction: "one-way", departure:

    Date.t(), return: nil, errors: [:return] } ▸ !

  105. ONLY 6 VALID STATES! ## one-way flight # one way

    flight %{direction: "one-way", departure: Date.t(), return: nil, errors: []} # one way flight with departure error %{direction: "one-way", departure: nil, return: nil, errors: [:departure]} ## two-way flight # two-way flight %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: []} # two-way flight with errors %{direction: "two-way", departure: nil, return: Date.t(), errors: [:departure]} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:return]} %{direction: "two-way", departure: nil, return: nil, errors: [:departure, :return]}

  106. ONLY 6 VALID STATES! ## one-way flight # one way

    flight %{direction: "one-way", departure: Date.t(), return: nil, errors: []} # one way flight with departure error %{direction: "one-way", departure: nil, return: nil, errors: [:departure]} ## two-way flight # two-way flight %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: []} # two-way flight with errors %{direction: "two-way", departure: nil, return: Date.t(), errors: [:departure]} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:return]} %{direction: "two-way", departure: nil, return: nil, errors: [:departure, :return]}

  107. ONLY 6 VALID STATES! ## one-way flight # one way

    flight %{direction: "one-way", departure: Date.t(), return: nil, errors: []} # one way flight with departure error %{direction: "one-way", departure: nil, return: nil, errors: [:departure]} ## two-way flight # two-way flight %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: []} # two-way flight with errors %{direction: "two-way", departure: nil, return: Date.t(), errors: [:departure]} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:return]} %{direction: "two-way", departure: nil, return: nil, errors: [:departure, :return]}

  108. ONLY 6 VALID STATES! ## one-way flight # one way

    flight %{direction: "one-way", departure: Date.t(), return: nil, errors: []} # one way flight with departure error %{direction: "one-way", departure: nil, return: nil, errors: [:departure]} ## two-way flight # two-way flight %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: []} # two-way flight with errors %{direction: "two-way", departure: nil, return: Date.t(), errors: [:departure]} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:return]} %{direction: "two-way", departure: nil, return: nil, errors: [:departure, :return]}

  109. ONLY 6 VALID STATES! ## one-way flight # one way

    flight %{direction: "one-way", departure: Date.t(), return: nil, errors: []} # one way flight with departure error %{direction: "one-way", departure: nil, return: nil, errors: [:departure]} ## two-way flight # two-way flight %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: []} # two-way flight with errors %{direction: "two-way", departure: nil, return: Date.t(), errors: [:departure]} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:return]} %{direction: "two-way", departure: nil, return: nil, errors: [:departure, :return]}

  110. INCLUDING ERRORS IN OUR DOMAIN MODEL @type date_or_error :: Date.t()

    | {:error, any()} @type flight_booker :: {:one_way, date_or_error} | {:two_way, date_or_error, date_or_error}

  111. INCLUDING ERRORS IN OUR DOMAIN MODEL @type date_or_error :: Date.t()

    | {:error, any()} @type flight_booker :: {:one_way, date_or_error} | {:two_way, date_or_error, date_or_error}

  112. INCLUDING ERRORS IN OUR DOMAIN MODEL @type date_or_error :: Date.t()

    | {:error, any()} @type flight_booker :: {:one_way, date_or_error} | {:two_way, date_or_error, date_or_error}

  113. INCLUDING ERRORS IN OUR DOMAIN MODEL @type date_or_error :: Date.t()

    | {:error, any()} @type flight_booker :: {:one_way, date_or_error} | {:two_way, date_or_error, date_or_error}

  114. INCLUDING ERRORS IN OUR DOMAIN MODEL @type date_or_error :: Date.t()

    | {:error, any()} @type flight_booker :: {:one_way, date_or_error} | {:two_way, date_or_error, date_or_error}

  115. POSSIBLE STATES IN OUR DOMAIN MODEL # one way {:one_way,

    Date.t()} {:one_way, {:error, any()}} # two way {:two_way, departure: Date.t(), return: Date.t()} {:two_way, departure: {:error, any()}, return: Date.t()} {:two_way, departure: Date.t(), return: {:error, any()}} {:two_way, departure: {:error, any()}, return: {:error, any()}}

  116. POSSIBLE STATES IN OUR DOMAIN MODEL # one way {:one_way,

    Date.t()} {:one_way, {:error, any()}} # two way {:two_way, departure: Date.t(), return: Date.t()} {:two_way, departure: {:error, any()}, return: Date.t()} {:two_way, departure: Date.t(), return: {:error, any()}} {:two_way, departure: {:error, any()}, return: {:error, any()}}

  117. POSSIBLE STATES IN OUR DOMAIN MODEL # one way {:one_way,

    Date.t()} {:one_way, {:error, any()}} # two way {:two_way, departure: Date.t(), return: Date.t()} {:two_way, departure: {:error, any()}, return: Date.t()} {:two_way, departure: Date.t(), return: {:error, any()}} {:two_way, departure: {:error, any()}, return: {:error, any()}}

  118. RENDERING COMPLEX TYPES <form phx-submit="book" phx-change="update"> <%= case @booker do

    %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <.departure_input departure={departure} /> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <.departure_input departure={departure} /> <.return_input return={return} /> <% end %> <%= submit "Book" %> </form>

  119. RENDERING COMPLEX TYPES <form phx-submit="book" phx-change="update"> <%= case @booker do

    %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <.departure_input departure={departure} /> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <.departure_input departure={departure} /> <.return_input return={return} /> <% end %> <%= submit "Book" %> </form>

  120. RENDERING COMPLEX TYPES <form phx-submit="book" phx-change="update"> <%= case @booker do

    %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <.departure_input departure={departure} /> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <.departure_input departure={departure} /> <.return_input return={return} /> <% end %> <%= submit "Book" %> </form>

  121. RENDERING COMPLEX TYPES <form phx-submit="book" phx-change="update"> <%= case @booker do

    %> <% {:one_way, departure} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "one-way" %> <.departure_input departure={departure} /> <% {:two_way, departure, return} -> %> <%= select :booking, :flight_type, ["one-way", "two-way"], value: "two-way" %> <.departure_input departure={departure} /> <.return_input return={return} /> <% end %> <%= submit "Book" %> </form>

  122. RENDERING COMPLEX TYPES (DEPARTURE INPUT) def departure_input(assigns) do ~H""" <%=

    case @departure do %> <% {:error, value} -> %> <%= text_input :booking, :departure, value: value, class: "invalid" %> <span class="invalid-feedback">is invalid</span> <% value -> %> <%= text_input :booking, :departure, value: value %> <% end %> """ end

  123. RENDERING COMPLEX TYPES (DEPARTURE INPUT) def departure_input(assigns) do ~H""" <%=

    case @departure do %> <% {:error, value} -> %> <%= text_input :booking, :departure, value: value, class: "invalid" %> <span class="invalid-feedback">is invalid</span> <% value -> %> <%= text_input :booking, :departure, value: value %> <% end %> """ end

  124. RENDERING COMPLEX TYPES (DEPARTURE INPUT) def departure_input(assigns) do ~H""" <%=

    case @departure do %> <% {:error, value} -> %> <%= text_input :booking, :departure, value: value, class: "invalid" %> <span class="invalid-feedback">is invalid</span> <% value -> %> <%= text_input :booking, :departure, value: value %> <% end %> """ end

  125. RENDERING COMPLEX TYPES (DEPARTURE INPUT) def departure_input(assigns) do ~H""" <%=

    case @departure do %> <% {:error, value} -> %> <%= text_input :booking, :departure, value: value, class: "invalid" %> <span class="invalid-feedback">is invalid</span> <% value -> %> <%= text_input :booking, :departure, value: value %> <% end %> """ end

  126. RENDERING COMPLEX TYPES (RETURN INPUT) def return_input(assigns) do ~H""" <%=

    case @return do %> <% {:error, value} -> %> <%= text_input :booking, :return, value: value, class: "invalid" %> <span class="invalid-feedback">is invalid</span> <% value -> %> <%= text_input :booking, :return, value: value %> <% end %> """ end

  127. RENDERING COMPLEX TYPES (RETURN INPUT) def return_input(assigns) do ~H""" <%=

    case @return do %> <% {:error, value} -> %> <%= text_input :booking, :return, value: value, class: "invalid" %> <span class="invalid-feedback">is invalid</span> <% value -> %> <%= text_input :booking, :return, value: value %> <% end %> """ end

  128. RENDERING COMPLEX TYPES (RETURN INPUT) def return_input(assigns) do ~H""" <%=

    case @return do %> <% {:error, value} -> %> <%= text_input :booking, :return, value: value, class: "invalid" %> <span class="invalid-feedback">is invalid</span> <% value -> %> <%= text_input :booking, :return, value: value %> <% end %> """ end

  129. RENDERING COMPLEX TYPES (RETURN INPUT) def return_input(assigns) do ~H""" <%=

    case @return do %> <% {:error, value} -> %> <%= text_input :booking, :return, value: value, class: "invalid" %> <span class="invalid-feedback">is invalid</span> <% value -> %> <%= text_input :booking, :return, value: value %> <% end %> """ end

  130. TRANSFORM USER INPUT (BEFORE) defp parse_params_into_booking(params) do case params do

    %{"flight_type" => "one-way", "departure" => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  131. TRANSFORM USER INPUT (BEFORE) defp parse_params_into_booking(params) do case params do

    %{"flight_type" => "one-way", "departure" => departure} -> departure |> Date.from_iso8601!() |> FlightBooker.one_way() %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> departure_date = departure |> Date.from_iso8601!() return_date = return |> Date.from_iso8601!() FlightBooker.two_way(departure_date, return_date) %{"flight_type" => "two-way", "departure" => departure} -> departure_date = departure |> Date.from_iso8601!() return_date = Date.utc_today() FlightBooker.two_way(departure_date, return_date) end end

  132. TRANSFORM USER INPUT (NOW) defp parse_params_into_booking(params) do case params do

    %{"flight_type" => "one-way", "departure" => departure} -> FlightBooker.one_way(departure) %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> FlightBooker.two_way(departure, return) %{"flight_type" => "two-way", "departure" => departure} -> return = Date.utc_today() |> Date.to_string() FlightBooker.two_way(departure, return) end end

  133. TRANSFORM USER INPUT (NOW) defp parse_params_into_booking(params) do case params do

    %{"flight_type" => "one-way", "departure" => departure} -> FlightBooker.one_way(departure) %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> FlightBooker.two_way(departure, return) %{"flight_type" => "two-way", "departure" => departure} -> return = Date.utc_today() |> Date.to_string() FlightBooker.two_way(departure, return) end end

  134. TRANSFORM USER INPUT (NOW) defp parse_params_into_booking(params) do case params do

    %{"flight_type" => "one-way", "departure" => departure} -> FlightBooker.one_way(departure) %{"flight_type" => "two-way", "departure" => departure, "return" => return} -> FlightBooker.two_way(departure, return) %{"flight_type" => "two-way", "departure" => departure} -> return = Date.utc_today() |> Date.to_string() FlightBooker.two_way(departure, return) end end

  135. PARSING INPUT INTO OUR DOMAIN def one_way(departure_value) do departure_value |>

    parse_date() |> build_one_way() end def two_way(departure_value, return_value) do departure = parse_date(departure_value) return = parse_date(return_value) build_two_way(departure, return) end

  136. PARSING INPUT INTO OUR DOMAIN def one_way(departure_value) do departure_value |>

    parse_date() |> build_one_way() end def two_way(departure_value, return_value) do departure = parse_date(departure_value) return = parse_date(return_value) build_two_way(departure, return) end

  137. PARSING INPUT INTO OUR DOMAIN defp parse_date(%Date{} = date), do:

    date defp parse_date(string_date) when is_binary(string_date) do case Date.from_iso8601(string_date) do {:ok, date} -> date {:error, _} -> error(string_date) end end defp parse_date(value), do: error(value) defp error(value), do: {:error, value}

  138. PARSING INPUT INTO OUR DOMAIN defp parse_date(%Date{} = date), do:

    date defp parse_date(string_date) when is_binary(string_date) do case Date.from_iso8601(string_date) do {:ok, date} -> date {:error, _} -> error(string_date) end end defp parse_date(value), do: error(value) defp error(value), do: {:error, value}

  139. PARSING INPUT INTO OUR DOMAIN defp parse_date(%Date{} = date), do:

    date defp parse_date(string_date) when is_binary(string_date) do case Date.from_iso8601(string_date) do {:ok, date} -> date {:error, _} -> error(string_date) end end defp parse_date(value), do: error(value) defp error(value), do: {:error, value}

  140. PARSING INPUT INTO OUR DOMAIN defp parse_date(%Date{} = date), do:

    date defp parse_date(string_date) when is_binary(string_date) do case Date.from_iso8601(string_date) do {:ok, date} -> date {:error, _} -> error(string_date) end end defp parse_date(value), do: error(value) defp error(value), do: {:error, value}

  141. PARSING INPUT INTO OUR DOMAIN defp parse_date(%Date{} = date), do:

    date defp parse_date(string_date) when is_binary(string_date) do case Date.from_iso8601(string_date) do {:ok, date} -> date {:error, _} -> error(string_date) end end defp parse_date(value), do: error(value) defp error(value), do: {:error, value}

  142. PARSING INPUT INTO OUR DOMAIN defp parse_date(%Date{} = date), do:

    date defp parse_date(string_date) when is_binary(string_date) do case Date.from_iso8601(string_date) do {:ok, date} -> date {:error, _} -> error(string_date) end end defp parse_date(value), do: error(value) defp error(value), do: {:error, value}

  143. PARSING INPUT INTO OUR DOMAIN defp parse_date(%Date{} = date), do:

    date defp parse_date(string_date) when is_binary(string_date) do case Date.from_iso8601(string_date) do {:ok, date} -> date {:error, _} -> error(string_date) end end defp parse_date(value), do: error(value) defp error(value), do: {:error, value}

  144. PARSING INPUT INTO OUR DOMAIN def one_way(departure_value) do departure_value |>

    parse_date() |> build_one_way() end def two_way(departure_value, return_value) do departure = parse_date(departure_value) return = parse_date(return_value) build_two_way(departure, return) end

  145. PARSING INPUT INTO OUR DOMAIN def one_way(departure_value) do departure_value |>

    parse_date() |> build_one_way() end def two_way(departure_value, return_value) do departure = parse_date(departure_value) return = parse_date(return_value) build_two_way(departure, return) end

  146. PARSING INPUT INTO OUR DOMAIN defp build_one_way(date) do {:one_way, date}

    end defp build_two_way(departure, return) do {:two_way, departure, return} end

  147. 26 INVALID STATES REMOVED # one-way %{direction: "one-way", departure: Date.t(),

    return: Date.t(), errors: []} %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: [:departure]} %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: [:return]} %{direction: "one-way", departure: Date.t(), return: Date.t(), errors: [:departure, :return]} %{direction: "one-way", departure: nil, return: Date.t(), errors: []} %{direction: "one-way", departure: nil, return: Date.t(), errors: [:departure]} %{direction: "one-way", departure: nil, return: Date.t(), errors: [:return]} %{direction: "one-way", departure: nil, return: Date.t(), errors: [:departure, :return]} %{direction: "one-way", departure: Date.t(), return: nil, errors: [:departure]} %{direction: "one-way", departure: Date.t(), return: nil, errors: [:return]} %{direction: "one-way", departure: Date.t(), return: nil, errors: [:departure, :return]} %{direction: "one-way", departure: nil, return: nil, errors: []} %{direction: "one-way", departure: nil, return: nil, errors: [:return]} %{direction: "one-way", departure: nil, return: nil, errors: [:departure, :return]} # two-way %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: [:departure]} %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: [:return]} %{direction: "two-way", departure: Date.t(), return: Date.t(), errors: [:departure, :return]} %{direction: "two-way", departure: nil, return: Date.t(), errors: []} %{direction: "two-way", departure: nil, return: Date.t(), errors: [:return]} %{direction: "two-way", departure: nil, return: Date.t(), errors: [:departure, :return]} %{direction: "two-way", departure: Date.t(), return: nil, errors: []} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:departure]} %{direction: "two-way", departure: Date.t(), return: nil, errors: [:departure, :return]} %{direction: "two-way", departure: nil, return: nil, errors: []} %{direction: "two-way", departure: nil, return: nil, errors: [:departure]} %{direction: "two-way", departure: nil, return: nil, errors: [:return]}

  148. 26 INVALID STATES REMOVED

  149. WE CANNOT MODEL EVERYTHING

  150. WE CANNOT MODEL EVERYTHING ▸ Validate what you cannot constrain

    with modeling

  151. VALIDATE WHAT YOU CANNOT CONSTRAIN WITH MODELING def book_trip({:two_way, departure,

    return}) do if Date.compare(departure, return) == :gt do {:error, "Departure cannot be after return"} else {:ok, "You have booked a two-way flight departing #{departure} and returning #{return}"} end end

  152. VALIDATE WHAT YOU CANNOT CONSTRAIN WITH MODELING def book_trip({:two_way, departure,

    return}) do if Date.compare(departure, return) == :gt do {:error, "Departure cannot be after return"} else {:ok, "You have booked a two-way flight departing #{departure} and returning #{return}"} end end

  153. VALIDATE WHAT YOU CANNOT CONSTRAIN WITH MODELING def book_trip({:two_way, departure,

    return}) do if Date.compare(departure, return) == :gt do {:error, "Departure cannot be after return"} else {:ok, "You have booked a two-way flight departing #{departure} and returning #{return}"} end end

  154. VALIDATE WHAT YOU CANNOT CONSTRAIN WITH MODELING def book_trip({:two_way, departure,

    return}) do if Date.compare(departure, return) == :gt do {:error, "Departure cannot be after return"} else {:ok, "You have booked a two-way flight departing #{departure} and returning #{return}"} end end

  155. !

  156. WHAT ABOUT ECTO?

  157. WHAT ABOUT ECTO? ▸ Well integrated with Phoenix forms

  158. WHAT ABOUT ECTO? ▸ Well integrated with Phoenix forms ▸

    Great casting helpers

  159. WHAT ABOUT ECTO? ▸ Well integrated with Phoenix forms ▸

    Great casting helpers ▸ Great validation helpers

  160. WHAT ABOUT ECTO? ▸ Well integrated with Phoenix forms ▸

    Great casting helpers ▸ Great validation helpers ▸ Use schemaless changesets as an anti-corruption layer

  161. WHAT ABOUT ECTO? Use Ecto as much as you can

  162. WHAT ABOUT ECTO? ! Ecto shines with maps (and structs)

  163. COMBINE SUM TYPES WITH ECTO CHANGESETS

  164. COMBINE SUM TYPES WITH ECTO CHANGESETS @type flight_booker :: {:one_way,

    date_or_error} | {:two_way, date_or_error, date_or_error}

  165. COMBINE SUM TYPES WITH ECTO CHANGESETS @type flight_booker :: {:one_way,

    date_or_error} | {:two_way, date_or_error, date_or_error}

  166. COMBINE SUM TYPES WITH ECTO CHANGESETS @type flight_booker :: {:one_way,

    Ecto.Changeset.t()} | {:two_way, Ecto.Changeset.t()}

  167. USE ECTO'S CASTING & ERROR GENERATION def one_way(departure_value) do departure_value

    |> parse_date() |> build_one_way() end def two_way(departure_value, return_value) do departure = parse_date(departure_value) return = parse_date(return_value) build_two_way(departure, return) end

  168. USE ECTO'S CASTING & ERROR GENERATION def one_way(departure_value) do departure_value

    |> parse_date() |> build_one_way() end def two_way(departure_value, return_value) do departure = parse_date(departure_value) return = parse_date(return_value) build_two_way(departure, return) end

  169. USE ECTO'S CASTING & ERROR GENERATION def one_way(departure_value) do %OneWay{}

    |> OneWay.changeset(%{departure: departure_value}) |> build_one_way() end def two_way(departure_value, return_value) do %TwoWay{} |> TwoWay.changeset(%{departure: departure_value, return: return_value}) |> build_two_way() end

  170. USE ECTO'S CASTING & ERROR GENERATION def one_way(departure_value) do %OneWay{}

    |> OneWay.changeset(%{departure: departure_value}) |> build_one_way() end def two_way(departure_value, return_value) do %TwoWay{} |> TwoWay.changeset(%{departure: departure_value, return: return_value}) |> build_two_way() end

  171. RENDERING COMPLEX TYPES <%= case @booker do %> <% {:one_way,

    changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "one-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= submit "Book", id: "book-flight" %> </.form> <% {:two_way, changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "two-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= text_input f, :return %> <%= error_tag f, :return %> <%= submit "Book", id: "book-flight" %> </.form> <% end %>

  172. RENDERING COMPLEX TYPES <%= case @booker do %> <% {:one_way,

    changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "one-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= submit "Book", id: "book-flight" %> </.form> <% {:two_way, changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "two-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= text_input f, :return %> <%= error_tag f, :return %> <%= submit "Book", id: "book-flight" %> </.form> <% end %>

  173. RENDERING COMPLEX TYPES <%= case @booker do %> <% {:one_way,

    changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "one-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= submit "Book", id: "book-flight" %> </.form> <% {:two_way, changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "two-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= text_input f, :return %> <%= error_tag f, :return %> <%= submit "Book", id: "book-flight" %> </.form> <% end %>

  174. RENDERING COMPLEX TYPES <%= case @booker do %> <% {:one_way,

    changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "one-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= submit "Book", id: "book-flight" %> </.form> <% {:two_way, changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "two-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= text_input f, :return %> <%= error_tag f, :return %> <%= submit "Book", id: "book-flight" %> </.form> <% end %>

  175. RENDERING COMPLEX TYPES <%= case @booker do %> <% {:one_way,

    changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "one-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= submit "Book", id: "book-flight" %> </.form> <% {:two_way, changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "two-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= text_input f, :return %> <%= error_tag f, :return %> <%= submit "Book", id: "book-flight" %> </.form> <% end %>

  176. RENDERING COMPLEX TYPES <%= case @booker do %> <% {:one_way,

    changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "one-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= submit "Book", id: "book-flight" %> </.form> <% {:two_way, changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "two-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= text_input f, :return %> <%= error_tag f, :return %> <%= submit "Book", id: "book-flight" %> </.form> <% end %>

  177. RENDERING COMPLEX TYPES <%= case @booker do %> <% {:one_way,

    changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "one-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= submit "Book", id: "book-flight" %> </.form> <% {:two_way, changeset} -> %> <%= select :booker, :flight_type, ["one-way", "two-way"], phx_click: "change-flight-type", value: "two-way", id: "flight-type" %> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= text_input f, :return %> <%= error_tag f, :return %> <%= submit "Book", id: "book-flight" %> </.form> <% end %>

  178. RENDERING COMPLEX TYPES <%= case @booker do %> <% {:one_way,

    changeset} -> %> <button type="button" phx-click="change-flight-type" value="two-way">Two-way</button> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= submit "Book", id: "book-flight" %> </.form> <% {:two_way, changeset} -> %> <button type="button" phx-click="change-flight-type" value="one-way">One-way</button> <.form let={f} for={changeset} phx-submit="book" phx-change="update"> <%= text_input f, :departure %> <%= error_tag f, :departure %> <%= text_input f, :return %> <%= error_tag f, :return %> <%= submit "Book", id: "book-flight" %> </.form> <% end %>

  179. HANDLE CHANGE OF STATE def handle_event("change-flight-type", %{"value" => "one-way"}, socket)

    do date = Date.utc_today() booker = FlightBooker.one_way(date) socket |> assign(:booker, booker) |> noreply() end def handle_event("change-flight-type", %{"value" => "two-way"}, socket) do date = Date.utc_today() booker = FlightBooker.two_way(date, date) socket |> assign(:booker, booker) |> noreply() end

  180. HANDLE CHANGE OF STATE def handle_event("change-flight-type", %{"value" => "one-way"}, socket)

    do date = Date.utc_today() booker = FlightBooker.one_way(date) socket |> assign(:booker, booker) |> noreply() end def handle_event("change-flight-type", %{"value" => "two-way"}, socket) do date = Date.utc_today() booker = FlightBooker.two_way(date, date) socket |> assign(:booker, booker) |> noreply() end

  181. HANDLE CHANGE OF STATE def handle_event("change-flight-type", %{"value" => "one-way"}, socket)

    do date = Date.utc_today() booker = FlightBooker.one_way(date) socket |> assign(:booker, booker) |> noreply() end def handle_event("change-flight-type", %{"value" => "two-way"}, socket) do date = Date.utc_today() booker = FlightBooker.two_way(date, date) socket |> assign(:booker, booker) |> noreply() end

  182. HANDLE CHANGE OF STATE def handle_event("change-flight-type", %{"value" => "one-way"}, socket)

    do date = Date.utc_today() booker = FlightBooker.one_way(date) socket |> assign(:booker, booker) |> noreply() end def handle_event("change-flight-type", %{"value" => "two-way"}, socket) do date = Date.utc_today() booker = FlightBooker.two_way(date, date) socket |> assign(:booker, booker) |> noreply() end

  183. HANDLE CHANGE OF STATE def handle_event("change-flight-type", %{"value" => "one-way"}, socket)

    do date = Date.utc_today() booker = FlightBooker.one_way(date) socket |> assign(:booker, booker) |> noreply() end def handle_event("change-flight-type", %{"value" => "two-way"}, socket) do date = Date.utc_today() booker = FlightBooker.two_way(date, date) socket |> assign(:booker, booker) |> noreply() end

  184. HANDLE FORMS def handle_event("update", %{"one_way" => params}, socket) do %{"departure"

    => departure} = params booker = FlightBooker.one_way(departure) socket |> assign(:booker, booker) |> noreply() end def handle_event("update", %{"two_way" => params}, socket) do %{"departure" => departure, "return" => return} = params booker = FlightBooker.two_way(departure, return) socket |> assign(:booker, booker) |> noreply() end

  185. HANDLE FORMS def handle_event("update", %{"one_way" => params}, socket) do %{"departure"

    => departure} = params booker = FlightBooker.one_way(departure) socket |> assign(:booker, booker) |> noreply() end def handle_event("update", %{"two_way" => params}, socket) do %{"departure" => departure, "return" => return} = params booker = FlightBooker.two_way(departure, return) socket |> assign(:booker, booker) |> noreply() end

  186. HANDLE FORMS def handle_event("update", %{"one_way" => params}, socket) do %{"departure"

    => departure} = params booker = FlightBooker.one_way(departure) socket |> assign(:booker, booker) |> noreply() end def handle_event("update", %{"two_way" => params}, socket) do %{"departure" => departure, "return" => return} = params booker = FlightBooker.two_way(departure, return) socket |> assign(:booker, booker) |> noreply() end

  187. HANDLE FORMS def handle_event("update", %{"one_way" => params}, socket) do %{"departure"

    => departure} = params booker = FlightBooker.one_way(departure) socket |> assign(:booker, booker) |> noreply() end def handle_event("update", %{"two_way" => params}, socket) do %{"departure" => departure, "return" => return} = params booker = FlightBooker.two_way(departure, return) socket |> assign(:booker, booker) |> noreply() end

  188. HANDLE FORMS def handle_event("update", %{"one_way" => params}, socket) do %{"departure"

    => departure} = params booker = FlightBooker.one_way(departure) socket |> assign(:booker, booker) |> noreply() end def handle_event("update", %{"two_way" => params}, socket) do %{"departure" => departure, "return" => return} = params booker = FlightBooker.two_way(departure, return) socket |> assign(:booker, booker) |> noreply() end

  189. ! EXPLORATION NOTES

  190. ! EXPLORATION NOTES ▸ Model your domain to remove invalid

    states

  191. ! EXPLORATION NOTES ▸ Model your domain to remove invalid

    states ▸ ! Render complex types Declaratively & Exhaustively

  192. ! EXPLORATION NOTES ▸ Model your domain to remove invalid

    states ▸ ! Render complex types Declaratively & Exhaustively ▸ Parse raw ⚠ unsafe values into your domain values

  193. ! EXPLORATION NOTES ▸ Model your domain to remove invalid

    states ▸ ! Render complex types Declaratively & Exhaustively ▸ Parse raw ⚠ unsafe values into your domain values ▸ ✅ Validate what you cannot constrain

  194. ! EXPLORATION NOTES ▸ Model your domain to remove invalid

    states ▸ ! Render complex types Declaratively & Exhaustively ▸ Parse raw ⚠ unsafe values into your domain values ▸ ✅ Validate what you cannot constrain ▸ Combine powers with Ecto $ when dealing with maps

  195. GERMAN VELASCO GERMANVELASCO.COM

  196. THANK YOU GERMANVELASCO.COM

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