Book Changeset

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"},
  {:ecto, "~> 3.9"}
])

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Book Changeset

You’re going to create a Book schemaless changeset struct. A book should have:

• A required :title field between 3 and 100 characters.
• A required :content string field.
• A :published_on date field.
• A :category field which must be either "action", "fiction", or "mystery" (you may choose to add more categories if you wish)
• A :books_sold integer which must be 0 or above.
• A :publisher_email field which must be in the format name@domain.extension
• An :author string field.
• An :has_license field which must always be true.
• A :price integer field which must be above 0.

For example, creating a book with the following invalid fields would return an {:error, changeset} tuple similar to the following.

Book.new(%{category: "invalid", email: "invalid", books_sold: -1, price: -1})
{:error,
 #Ecto.Changeset<
   action: :update,
   changes: %{books_sold: -1, category: "invalid", price: -1},
   errors: [
     price: {"must be greater than %{number}",
      [validation: :number, kind: :greater_than, number: 0]},
     has_license: {"must be accepted", [validation: :acceptance]},
     books_sold: {"must be greater than or equal to %{number}",
      [validation: :number, kind: :greater_than_or_equal_to, number: 0]},
     category: {"is invalid", [validation: :inclusion, enum: ["action", "fiction", "mystery"]]},
     title: {"can't be blank", [validation: :required]},
     content: {"can't be blank", [validation: :required]}
   ],
   data: #Book<>,
   valid?: false
 >}

Hint

Read the Ecto.Changeset documentation. There, you’ll find all of the validate* functions necessary for each field. For example, Ecto.Changeset.validate_change/3 allows you to create custom validation.

You can also refer to the primitive types documentation for the list of allowed field types.

Example Solution

defmodule Book do
  @types %{
    title: :string,
    content: :string,
    published_on: :date,
    category: :string,
    books_sold: :integer,
    publisher_email: :string,
    author: :string,
    has_license: :boolean,
    price: :integer
  }

  @keys Map.keys(@types)
  
  defstruct @keys

  def changeset(%__MODULE__{} = user, params \\ %{}) do
    {user, @types}
    |> Ecto.Changeset.cast(params, @keys)
    |> Ecto.Changeset.validate_required([:title, :content])
    |> Ecto.Changeset.validate_length(:title, min: 3, max: 100)
    |> Ecto.Changeset.validate_inclusion(:category, ["action", "fiction", "mystery"])
    |> Ecto.Changeset.validate_number(:books_sold, greater_than_or_equal_to: 0)
    |> Ecto.Changeset.validate_change(:publisher_email, fn :publisher_email, publisher_email ->
      if Regex.match?(~r/\w+@\w+\.\w+/, publisher_email) do
        []
      else
        [email: "invalid email"]
      end
    end)
    |> Ecto.Changeset.validate_acceptance(:has_license)
    |> Ecto.Changeset.validate_number(:price, greater_than: 0)
  end

  def new(params) do
    %__MODULE__{}
    |> changeset(params)
    |> Ecto.Changeset.apply_action(:update)
  end
end

You should rely on Ecto Changesets and your own custom validation to validate the book information. Enter your solution below.

defmodule Book do
end

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "book_changeset_reading"
    "exercises" -> "book_changeset_exercise"
  end

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, save_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(
      progress_path,
      Jason.encode!(Map.put(existing_progress, save_name, completed), pretty: true)
    )
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout -b book-changeset-exercise
$ git add .
$ git commit -m "finish book changeset exercise"
$ git push origin book-changeset-exercise

Create a pull request from your book-changeset-exercise branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your teacher by including @BrooklinJazz in your PR description to get feedback. You (or your teacher) may merge your PR into your solutions branch after review.

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